Perfect Toast Every Time! - Page 1
Forum section: electronics / projects

author: Beeper
author_rank: Contributor
timestamp: November 06, 2014, 02:43:22 pm
content: Me and my girlfriend have very different ideas on how to toast bread. She likes it light, I like it browned. She has a toaster that stopped working, it was just a cold solder joint on the browning adjustment pot that is turned by a knob on the side of the toaster, so I fixed it, it works ok again, but why should I settle for just OK?I want to upgrade the 555-timer circuit used in the toaster now with a state of the art micro-controller.The toaster always works well when first used and cold, but after heating up, I must always remember to retard the brownness adjustment knob (it adjusts a pot on the internal circuit board) to keep the toasting from too-toasting after the first set of slices.The toaster does have a thermistor hanging off the 555 control board for toaster cabinet heating compensation with many-slice toasting, but this simple 555 circuit just doesn't quite give me the results I want.I am experienced with PIC and C-language and Arduino microntrollers and know how to make electronic circuits work, know how to get a MCU A2D working with a thermistor. And i already have the circuit board size, with the pot position's layout and it's power supply circuit can be easily made to regulate 5V for the MCU. This makes it somewhat easy to convert this toaster to micro-controller operation. And I know how to make breadboard a circuit, make the PCB, power the MCU, sense the temperature, program a MCU for function as a timer.I just have to get it my MCU to set timing correctly each time, sot that it compensates for toasting heating effects by getting a reading form the thermistor for feedback.Has anyone made some programming strategy to work with the common toaster, to artfully get a MCU to activate the magic solonoid that makes the bread jump out at the perfect time?Is trail and error, toast and burn, the only way I am left to to somehow perfect the perfect toaster?I realize the following variables:Bread Moisture ContentSmoothness of Bread SurfaceBread inserted's initial Temperature/Thickness/DensityWhether there are 1 or two slices to toast.Multi-Toast Toasting Time Effects because of internal cabinet heat-up after the first toasting.Maybe it would require me to guess how to preset the browness knob just once to help the MCU to get it right.

author: tom66
author_rank: Super Contributor
timestamp: November 06, 2014, 02:56:22 pm
content: I am reminded of this.....http://kcbx.net/~tellswor/bettoast.htm

author: jc101
author_rank: Frequent Contributor
timestamp: November 06, 2014, 03:14:21 pm
content: I have a see through toaster, so it's always just right every time...http://www.magimix.uk.com/products/BREAKFAST/Toaster/Vision-Toaster/

author: Excavatoree
author_rank: Frequent Contributor
timestamp: November 06, 2014, 03:21:32 pm
content: More powah!!!!!!!!!!

author: Beeper
author_rank: Contributor
timestamp: November 06, 2014, 03:23:19 pm
content: One toasting effect I have just noticed: Although the toast seems to slowly rise to a browning temperature, once browning begins, the browning effect very quickly progresses from tan to brown to black. Time is of the essence, else essence is smoke.I think this is what your diagram shows, 3roomlab, but the slope from tan to black is quite steeper.I think this is what is going on: The bread heats slowly and probably linearly until bread surface moisture is evaporated. During this time the bread exposed surfaces have a low thermal resistance and bread surface heat is quickly conducted to the core of the slice, cooling the toast surface and the toaster by conduction and moisture evaporation. Also moisture is likely diffusing at first to the surface area and this sustains a slow temperature rise of the the surface toasting area.Once surface moisture has been exhausted, heat transfer to the bread surface is very rapid as the thermal resistance of the bread's surface becomes very high and browning proceeds very rapidly.

author: Beeper
author_rank: Contributor
timestamp: November 06, 2014, 03:44:45 pm
content: All I know is that you can buy croutons and they are all perfectly toasted and I couldn't make the payments on my Maserati if I bought one of these elegant toasters shown by other posters.

author: IanB
author_rank: Super Contributor
timestamp: November 06, 2014, 03:54:31 pm
content: I would try to design an optical technique. Have a light sensor aimed at the toast and use it to measure the change in light reflection as the toast browns.

author: Beeper
author_rank: Contributor
timestamp: November 06, 2014, 04:01:36 pm
content: IanB: A great idea, I wonder how to implement these optical components? How would you mount them, get them to fit into a stainless-steel-two-slicer, top-loading, push-the-lever-down-to-toast-after-setting-browness-knob 555 animated toaster?

author: m100
author_rank: Regular Contributor
timestamp: November 06, 2014, 04:02:30 pm
content: You want perfect toast? Just how stable is your mains supply voltage? Is your bread always fresh and baked exactly the same every day? Do you use stale bread to make toast, if so how many days since you bought the bread? What temperature is it kept at? What is the room temperature? What about the relative humidity? What happens post pop up if you don't remove the toast immediately, does the residual heat affect the finished product?Lots of variables, could be an interesting project but personally I'd either either watch it, delgate it or if I ever win the lottery employ someone to do it for me.

author: Beeper
author_rank: Contributor
timestamp: November 06, 2014, 04:07:09 pm
content: M100, this is an expermenter-hobby-DYI board. The spirit should be to attempt the possible, even attempt the likely impossible, not hire someone else to have all the fun! I think this board is a place to learn about electronics, programming, etc.Not every multi-million $$$ space rocket makes it far off the earth, as the news has recently shown, but one must enjoy trying.If it can work fairly well with a 555 circuit, why not try for MCU?BTW, we usually buy the same type of bread, I do have a favorite, and sometimes we keep the loaf inside the oven(without heat, of course) as a bread storage area, sometimes we shove the opened loaf into the fridge. So the raw materials are consistent, the room temperature gets cooler in winter, but the toaster doesn't seem to care that much.

author: lapm
author_rank: Frequent Contributor
timestamp: November 06, 2014, 04:22:14 pm
content: If i would be doing this i would at first limit variables in just couple you can control: Time, starting temperature and goal temperature.From these you can do things such as heat profiles, etc...Of course you need ability to reliable measure brownes of end result so you have feedback to all these functions...Maybe integrate heat exposure over time to slice of bread? and observe effect is has for color of end result?

author: miguelvp
author_rank: Super Contributor
timestamp: November 06, 2014, 04:29:45 pm
content: PID controller like the many reflow oven controllers available everywhere will do the trick.Record your profile for what is your perfect toast per user. Then you can select what user and type of bread or whatever other variants you need and make sure the controller keeps follows the profile.and on the plus side you can use it on a separate and dedicated toaster oven for reflowing your boards, maybe get a separate thermometer for each so you don't get lead contamination on your toast.

author: Unknown
author_rank: Unknown
timestamp: November 06, 2014, 04:32:12 pm
content: We have a Dualit toaster, so I just take a guess based on the type of bread etc and then just spin the mechanical timer dial - easy!

author: denelec
author_rank: Regular Contributor
timestamp: November 06, 2014, 09:58:14 pm
content: Quote from: IanB on November 06, 2014, 03:54:31 pmI also think it's a good idea.The problem will be to protect the sensor from the heat.I remember, when I was a kid, our toaster always burned the first toast...

author: Someone
author_rank: Super Contributor
timestamp: November 06, 2014, 11:00:59 pm
content: Quote from: Beeper on November 06, 2014, 03:23:19 pmAs you go on to note, its that the temperature will runaway when you are using the traditional radiative heating approach.Quote from: Beeper on November 06, 2014, 03:44:45 pmTemperature is the key, if you toast with a contact method (sandwich press) and set the temperature accurately you can chose a level of brown and leave the bread in there almost indefinitely without burning. The crouton factory is probably using a large continuous process with a well controlled and uniform temperature forced air oven.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: November 06, 2014, 11:33:01 pm
content: nice projectwill be fun to test if it work correctly every morningi think that the heating energy is what you should take attention to, i think for the first bread when toaster is cold , the heating energy is slowly exchanged due to the fact that both toaster and bread are room temperature and there temperature increase with " equal " rate, so the total heating energy is equal to an integral of temperature difference multiply by some factor over the total heating time. Things will no be the same for the second bread that will receive much more heating energy if exposed to that maximum heat for the same time.long story short , measure the room temperature for the first run before start heating, then calculate the needed time to transfer the same heating energy as the first time. The first heating time will be determined by the knob. Try to put that heat transfer into some imperial formula and you will get some precise result.Some useful data :Q = M Cp ?Twhere Q is energyM bread weightCp thermal capacity , for the bread it's 2.93Kj/(Kg . °C) (someone actually measured it)?T temperature difference between toaster temperature and bread (room) temperature.andP = Q/twhere P power used , t heating timeI think what you need to do is make sure that power is the same overtime for all your bread

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 12:24:18 am
content: I realize in attempting this toaster improvement project that practical limitations such as safety, cost and time must limit the end result. My MCU toaster may not always toast to perfection, but I am aiming to create a toaster that does better than the 555 solution.May God, grant me the serenity to accept the burnt bread I cannot toast,The courage to try to find the way to better toast the bread I can,And the MCU wisdom to know the difference.Toaster's Anonymous Prayer

author: moffy
author_rank: Super Contributor
timestamp: November 07, 2014, 12:25:46 am
content: I think you will need to use a feedback mechanism, like optical, because the variables are very variable. For raisin toast you have to shorten the time, for english muffins they need a long time with white bread somewhere in between. Maybe if you used a smoke detector with a variable threshold you could control the browning effect.

author: Macbeth
author_rank: Super Contributor
timestamp: November 07, 2014, 12:49:50 am
content: I believe you are missing the most important factor in making good toast - how to apply the butter in the perfect quantity and at what temperature to spread it. Nobody likes soggy toast.Thankfully some very important research was done byLeeds University over 10 years ago.. I am sure your perfect toaster could indicate when to arm the butter knife, measure the butter temperature and weight on the blade, and indicate the right time to strike the pats of butter after the toast has been ejected at its perfect toasty browning.The one thing I hate about perfect buttered toast is it has to be eaten at exactly the right time, once it cools it loses its magnificence as the ambrosia of the gods. Toast racks should be electronically heated and monitored. Also chucky eggs and soldiers - the soldiers are all cold by the time they get to the egg dipping stage.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 12:56:51 am
content: Just some idea. I am still brainstorming my project before committing to its implementation.Firstly, the 555-timer circuit does a pretty good job, I only want or probably need to get a MCU to do a better job.The key to toasting success with the original 555 design was to become a sophisticated toast maker. After a few slices of my favorite bread, I could correctly re-position the browning control to compensate for a heated toaster or compensate for the few different types of bread and bread temperatures I would encounter.I just want a MCU to somehow get close to getting toasting right without me having to fiddle around with some bureaucratic toaster user interface having some fancy LCD screen or many pots to set moisture content, mass, initial temperature, etc.What I will finally make must be simple to use.But maybe I can accept adding a few momentary-contact buttons to give the toaster MCU some insight into the specific toasting task? A button for thick bread, cold bread, for instance? And tiny LED's to indicate these toasting customizations have been turned on for the current toasting session?I just have to find some safe, clever way to make my toaster work better, I don't need perfect and neither me or my girlfriend will tolerate a complicated setup or toaster operation.I have salvaged some infrared motion detectors from an automatic light that detects the presence of moving humans in it's vicinity. I wonder if I can somehow embed a single glass fiber optic to be positioned close to the surface of the toast and safely couple infrared light within this very thin heat-resistant thread of glass to some sensor on the PCB and get an idea of the heat radiated from the surface of the toast toasting to give me an idea of the toast surface temperature? The problem is that with these types of infrared detectors, they want to detect moving objects, while a toasting slice sits still during the hot ride it is on.Would an infrared sensor(such as above) detect the rate of change of temperature at the critical start of toast temperature?I also know that I can purchase an infrared hand-held temperature meter that can accurately see the heat of a remote object, and I can cheaply buy this instrument this week on sale at a local store. In this way I can measure the surface temperature of the perfectly toasted toast at the instant of its final ejection.I can easily control the heating elements with a TRIAC and PWM to preheat the toaster(and the bread) to some standard temperature, thereby normalizing the starting temperature. The main consideration here is that this operation must not take too long. I would accept about a minute or so of first slice use "calibration" by the toaster.At the same time, I do not want to dry out the bread during this calibration.I have a theory: Once the surface of the bread reaches some critical temperature, the optimal brown to perfection toasting time can be accurately approximated by the MCU to correctly then apply the coup-de-gras heat dose.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:09:27 am
content: I think that Hamdi.fn is on to the right approach, I must just find the correct heat dosing and and a way to sense it.I just wonder how much time it would take to develop method to get meaningful data about the thermal dynamics of the the toast and the toaster. I do not want spending too much time in R & D effort.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:14:32 am
content: I would not be as concerned as Macbeth as to buttering my toast.I greatly enjoy upon wake up two slices of my favorite: toasted multi-grain bread upon which I apply peanut-butter and marmalade, but my girlfriend just wants a lightly toasted slice to go with her morning coffee.

author: pickle9000
author_rank: Super Contributor
timestamp: November 07, 2014, 01:21:52 am
content: Talkie Toaster

author: Macbeth
author_rank: Super Contributor
timestamp: November 07, 2014, 01:23:13 am
content: Quote from: Beeper on November 07, 2014, 01:14:32 amOh no, I think we have one of our colonials here. PBJ? for breakfast? bleurgh!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 07, 2014, 01:24:28 am
content: Quote from: Macbeth on November 07, 2014, 12:49:50 amI freeze sliced bread, and keep butter in the fridge. When the time comes I slice off chunks of butter, put them on the frozen bread and put it all in a toaster over, flat of course.When you get it just right, the butter sizzles and juuuuust starts to brown itself as it soaks into the hot bread.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:32:23 am
content: BTW, one thing I love about this old toaster is that when it ejects the bread, it really sends them flying out of the toaster to be then catched by a plate sitting nearby to its left.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:50:18 am
content: I have another theory: Once the surface of the bread starts to show some critical rapid rate of temperature rise, the optimal brown to perfection toasting time can be accurately approximated by the MCU to correctly then apply the coup-de-gras heat dose.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 02:14:39 am
content: Macbeth, when I was visiting London, staying at a B & B near the airport, everyday morning there was offered at breakfast fried bread! ( and pasteurized orange juice and greasy pork sausage!)bleurgh!

author: Bored@Work
author_rank: Super Contributor
timestamp: November 07, 2014, 06:57:52 am
content: Quote from: Beeper on November 06, 2014, 02:43:22 pmCost of two new toasters - 120 EuroCost of a sharpie for marking knob positions on the toaster - 2 EuroPeace and quiet in the marriage - Priceless

author: _Sin
author_rank: Regular Contributor
timestamp: November 07, 2014, 07:14:17 am
content: Quote from: Beeper on November 07, 2014, 02:14:39 amI can only apologise on behalf of my nation for your OJ experience. Sadly the British orange crop has been less than abundant in recent years, and importing whole oranges just for the juice is a bit wasteful...Fried bread and greasy pork sausages on the other hand, are key components of the breakfast of champions (though for the real thing you might have to head North of London to the tune of 400 miles, where the fried starch component is supplemented with a tattie scone and the sausage flattened and de-skinned to more efficiently absorb the cooking fat).

author: mzzj
author_rank: Super Contributor
timestamp: November 07, 2014, 07:47:19 am
content: Quote from: Beeper on November 07, 2014, 12:56:51 amI think infrared temperature sensor and/or brownness detector are the best possibilities.Something like this:https://www.sparkfun.com/products/9570Or how about some electrical nose that will determine the correct toast degree based on smell?More measurements would be required.

author: _Sin
author_rank: Regular Contributor
timestamp: November 07, 2014, 08:42:29 am
content: I'm not convinced by those suggesting an optical approach to detecting 'brownness' in terms of getting the perfect toast - I think doing that right will be non-trivial.Conceptually it's fine because I certainly know what the toast I want should *look* like, but I have trouble relating that to an arbitrary number on a dial, even on a toaster I'm familiar with.Unless you're always toasting the same bread, and it's very uniform in appearance and you never stick the heel of the loaf in, then the results will be quite varied and thus the toaster will not be easy to use.A white loaf generally toasts to a golden brown. A brown loaf toasts to a slightly darker brown. A loaf with fruit in will change unevenly. Marbled bread all bets are off.If you *did* go down this route, and the above assumptions (and perhaps more - lighting conditions, especially under the glare of the changing heating element?) can't be assumed, then I think you'd need a good way to quickly specify *how* brown you want the toast, relative to how it starts. And that needs to be intuitive so you don't incinerate brown bread, etc.My ideal interface would probably show an image of the untoasted slice on a screen, with a simulation of what it will look like after toasting. Set the dial until the image looks like what you want, and toast away.Great, now I want to build a toaster. And also I want toast.Mostly toast.

author: EEVblog
author_rank: Unknown
timestamp: November 07, 2014, 08:48:52 am
content: I was offered a job once at a small design house that had a patent on new toaster that used temperature controlled metal plates against the bread that ramped up and temp the toast a certain temp to ensure the most optimal result. And it could never burn.Toasters were a running joke on another forum I was on at the time, so I didn't want to be known as a Toaster Designer!

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 12:23:04 pm
content: mzzj has the right sensor, but how do I somehow protect it from the heating elements and yet position its point of view directly at the, say, near the middle of the toast's surface?I don't really know yet how to somehow keep this sensor far away from the toasting elements yet optically give it a clear view of a tiny spot on the center of the toast toasting. Whatever I do, it must be safe and yet robust in construction. I don't want any wires, PCB material or sensors burning to offer more flavor to the toast or encounter the sensor somehow getting entangled with mechanical moving toaster parts or especially with the inserted bread. I can't have it's field of view quickly fouled by crumbs from the toast.The sensor can only handle 85-deg C.I do have some #28 AWG silver coated solid copper Teflon wire-wrap wire, but I would only feel comfortable with this sensor mounted safely away from the heating elements, I want it sitting on the PCB.Somehow this sensor must see through the material supporting the toaster's heating elements and not see the blazing heat of the heating element wires nearby.The MLX90614 thermometer is small, very nice. It is factory calibrated in wide temperature ranges: -40 to 85°C for the ambient temperature and -70 to 382.2°C for the object temperature. The measured value is the average temperature of all objects in the Field Of View of the sensor. The MLX90614 offers a standard accuracy of 0.5°C around room temperatures.Will a single tiny strand of glass fiber optical fiber do the job?Will the optical fiber accept the very low freq. heat infrared when it is likely optimized for visible to UV light?Will it only allow light input along its length and not from the sides facing the heating elements?How can I safely and securely mount this optical coupling fiber to the heating element area?I need some light weight, small diameter, non-toxic material that functions as a high temp resistant light tube, should I call NASA now to get to work on it as a favor to all those countless millions of people that love their proper toast in the morning?

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 12:36:41 pm
content: EEVBLOG, In my IMHO you would be admired by all geeks, engineers and toast lovers all over the world. No one has yet accomplished the engineering task of adapting the so easy to manufacture and cheap to make and use of a push-the-lever-down-two-slice-toaster design to consistently give the desired toasted result!It is indeed a very challenging engineering problem worthy of the Nobel Prize.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:08:04 pm
content: __Sin, thank you for your input, but you've got all the right arguments for the wrong sensor, it is temperature alone, I think, that is the key. We should not be trying to get a image to try to figure out the completion status of a varying toasting object.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:14:28 pm
content: So, at this point all I know is that the key to toasting success with the original 555 design was to become a sophisticated toast maker. After burning a few slices of my favorite bread, I could correctly re-position the browning control to compensate for a heated toaster or compensate for the few different types of bread and bread temperatures I would encounter.Alas, by the next morning, I usually have forgotten or confused all my expert "settings."What's worse: If I make my toast at my girlfriends house and then forget to reset the Browness Control to her "very lightly toasted" desired setting, then I quickly find myself in the doghouse with her! It's something like not resetting the toilet seat cover, but somehow very more important.

author: _Sin
author_rank: Regular Contributor
timestamp: November 07, 2014, 01:20:08 pm
content: Quote from: Beeper on November 07, 2014, 01:08:04 pmI'll be interested to see how you get on with that - I'm kind of sceptical that you can consistently decide when things are toasted to the same degree just from the temperature. If the results are in any way reliant on the temperature profile of the heating cycle (including ambient effects such as room temp and even the bread temp) and/or the make-up or structure of the bread, then the temperature of the toast might not be a reliable indicator, nor entirely intuitive to alter depending on what you're toasting...

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 01:28:04 pm
content: _Sin, thanks again for your insight, you could be right and I failed to clarify my reason to chose temperature over imaging .I am not considering temperature alone, but rate of change of temperature.My theory(yet unproven) is that there exists a critical point, that it would be possible to detect a point in the toasting cycle where there is noticed a fast rate of change of temperature, and this time point would clearly give the MCU the correct feedback that toasting is very close to completion.

author: Beeper
author_rank: Contributor
timestamp: November 07, 2014, 02:04:40 pm
content: Hmmm, maybe something like this?https://www.tindie.com/products/PureEngineering/flir-lepton-thermal-camera-breakout-2/

author: robrenz
author_rank: Super Contributor
timestamp: November 07, 2014, 02:52:53 pm
content: IMO the perfect toaster would have tiled array of 20mm square independent heater and optical pickup zones on each side of the bread. This would cure the uneven browning situation that inevitably occurs and all the other variables.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 07, 2014, 03:09:01 pm
content: Quote from: _Sin on November 07, 2014, 07:14:17 amAll OJ from a box is pasteurized, the companies hire perfume experts to put back some essential oils to make it taste better.How else can you get OJ year round that always tastes exactly the same?

author: Macbeth
author_rank: Super Contributor
timestamp: November 07, 2014, 03:42:57 pm
content: Quote from: robrenz on November 07, 2014, 02:52:53 pmThis. Also you could fashion 8-bit pixel style images of Jesus and Virgin Mary on the toast and declare them a miracle and make your toaster a place of pilgrimage, fleecing the tourists for a slice. It could be more profitable than Lourdes.

author: miguelvp
author_rank: Super Contributor
timestamp: November 07, 2014, 03:45:39 pm
content: Quote from: Macbeth on November 07, 2014, 03:42:57 pmGoogle "selfie toaster" we are getting one for our daughter for xmas, she is in college so the plan is for her to put it in the common area kitchen.

author: robrenz
author_rank: Super Contributor
timestamp: November 07, 2014, 03:47:10 pm
content: Quote from: robrenz on November 07, 2014, 02:52:53 pmThis would also allow heat profiles ranging from toasted through where the bread is crispy throughout like melba toast to a crispy brown surface with a still soft core.

author: mikerj
author_rank: Super Contributor
timestamp: November 07, 2014, 04:11:21 pm
content: 216 seconds at 154 Celsiusmight be a good starting point.A long time ago I remember seeing a news article about a toaster being developed which used a sensor to detect the caramelisation of the sugars produced by the Maillard reaction (the process that causes browning). This was allegedly going to give absolutely perfect toast every time, but Google isn't showing me any currently available toasters that use this method, However it did findthis patent.

author: miguelvp
author_rank: Super Contributor
timestamp: November 07, 2014, 04:32:04 pm
content: Quote from: mikerj on November 07, 2014, 04:11:21 pmPretty much they used a reflow ovenBut again, don't use the same physical oven for both, I would even have an independent temperature sensor per toaster oven to avoid lead contamination.

author: m100
author_rank: Regular Contributor
timestamp: November 07, 2014, 05:07:36 pm
content: Quote from: mikerj on November 07, 2014, 04:11:21 pmIonisation chamber ? Radioactive Source? aka a smoke detector

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 12:54:39 am
content: Making the best toast (and butter)http://www.dailymail.co.uk/sciencetech/article-2017338/The-perfect-piece-toast-Scientists-test-2-000-slices-216-seconds-optimum-time.htmlandhttp://articles.economictimes.indiatimes.com/2011-07-25/news/29812639_1_toast-butter-joy

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 12:58:26 am
content: Scientists in Macbethland have figured it out, but they were using a toaster-oven. I am using a toaster!==========================http://hub.jhu.edu/magazine/2013/spring/engineering-perfect-toast....Minsky concentrated on toast, which turns out to be tricky. Blame it on browning. "Browning is a positive feedback process that is actually exquisitely sensitive," he says. "As the toast becomes brown, or darker, it starts to absorb much more infrared radiation from the heating elements, thereby quickening the heating process, causing it to brown faster and faster." A few extra seconds or degrees of heat, he says, can make or break a piece of toast. The perfect amount of browning is essential, Cowan says, to achieve the Maillard reaction—the chemical reaction between an amino acid and a reducing sugar that in bread's case leaves a brown color.Some researchers in the United Kingdom already had uncovered, or so they claimed, the recipe for perfect toast: heat at 154 degrees for 216 seconds. Using this as a base, Minsky and his team went to work tricking out an off-the-shelf toaster oven. They inserted a precision thermometer and connected it via relay to a controller that managed the heating process. The students then programmed the controller to maintain a constant temperature for the precise desired amount of time. The controller turned the heating element on and off if the interior conditions went above or below the specified temperature.The results, Minsky says, were delicious. "It was shockingly good. We thought the first slice might have been a fluke, but we used two whole loaves of bread and every piece we made was light and golden brown, just the perfect amount of crispiness."One small step for mankind.==========================They only used one type of bread!What would the result be with switching from white to wheat to rye or muffin?

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 01:35:00 am
content: Now, all have to do is figure out how to measure the temperature accurately.The single IC solution would not work placed inside since I cannot find a place inside the chamber that would in any worst case of operatioin limit the temperature of the IC to 85-deg C. (https://www.sparkfun.com/products/9570)If I drill a hole in the metal toasting shroud so that the IC can peek into a window(a drilled hole), on the edge-of-toast side of the toasting compartment then I must cover the hole with glass to prevent making an air draft inlet into the chamber. Maybe I can make a tiny PCB with standoffs that allows the IC to sit very close and peek in, but yet far enough away to prevent overheating? With this toaster there is plenty of room on the bread edge sides in the toaster cabinet to mount the IC on a PCB.Perhaps a thermocouple or oven metal thermistor probe could be the ideal solution here, I could easily drill a small hole and insert a thermocouple or probe inside the cooking chamber near the bottom of the toasting away from the lifting carriage. For the thermocouple, a twisted-pair of #28 Teflon wire-wrap wire could be used to carry the signal back to the PCB and the thermocouple is very small?I see they sell a cheap microwave temperature probe at the local Walmart, rugged, easy to insert into a hole near the bottom of the heating chamber.If I buy the infrared heat meter that was on sale this week I can easily measure the temperature from looking into the top of the toaster to easily calibrate any heat sensor.Any ideas what is the best choice?I could use PWM and a TRIAC with MCU control with a TRIAC instead of a relay. My toaster is rated at 750 watts, at 220V that would correspond to about 3.5 amps, so it would need a heatsink, but there is lots of room inside the toaster for a PCB.I could also use a relay for control like the scientists,, but it would be making clicking noises at it dithered around the setpoint. temperature.I see some problem with hot air venting at the top of the toaster, would this make the top of the toast a little less toasted because of cooling or would the heater compensate for this? I don't want to put a metal cap on the toaster! However, the toaster was working fine before the repair and I didn't notice any problem with uneven top to bottom toasting.I see the thermocouple solution and the single IC solution closer to being ideal than the temperature probe with its long metal casing giving it a slow response time, as the thermocouple and IC should have a very fast thermal response.The temperature probe's has a great advantage of being cheap and instant to acquire, so I could start work immediately on this project making a PCB and writing code. Perhaps the temperature doesn't change so fast, this probe idea may work well.

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 01:57:12 am
content: Another issue is how to raise the temperature to the exact point, I must be careful not to go too slow and dry out the toast or exhaust me or my girlfriend's patience, but I must reach the temperature without overshoot, even with some venting at the top.If the toast is already in the oven, at what point does timing start to get the exact time for perfect toast?What about the second set of slices, the timing must be different as the chamber is already hot?Or do I do as the scientist seemed to have done and start the timing the instant the temperature hits the target temperature?

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 03:00:54 am
content: Thermodynamics of the toasting chamber:I have some more theories about toasting: It is not the air temperature inside the toasting chamber as much as the radiant heat effect from the glowing heating wires that is responsible for creating the toasting effect. The above study points out that a darkening color change of the surface of the toast greatly increases the absorption of heat. I also have theorized that that the exhaustion of the evaporating effect due to moisture exhaustion causes a very steep rise of heat at the toast surface.As for heating, I theorize that:The only thing being heated, besides the mica sheets holding the heating element wires is air and the target toast, and if also the walls of the chamber are made of thin metal and conduct heat to the inside of the toaster cabinet, this is a small effect. Perhaps, once the chamber metal walls are near the target chamber, they might function to yield some thermal inertia, a heat capacitor effect, and this may tend to stabilize temperature a bit on the outer sides of the toast. But I have not noticed any difference in this toaster's ability to match the toasting color on both sides of the toast even with 555-timer operation.I also theorize that the heating elements are facing directly at the toast, so the temperature inside the toasting chamber is mostly moderated by the temperature of the air and the heating elements and the toast, and most importantly, radiant heat is responsible for most of the toasting effect, once the surface temperature of the toast reaches the target temperature due to heating to a point that exhausts surface moisture.So, I think the temperature of the air at the toast surface should be able to be very rapidly changed by PWM heater control.

author: IanB
author_rank: Super Contributor
timestamp: November 08, 2014, 03:10:37 am
content: Keep in mind that much of the toasting (most of it?) is done by radiation from the glowing heating elements. So the temperature inside the toasting chamber is much less important than the temperature of the toast surface. You might have more success with an IR thermometer pointed at the toast than with a thermocouple.

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 03:18:41 am
content: It seems that IanB and I have reached the same conclusion at the same time about the importance of radiant heat. Thank you for your ideas. I have spent some time thinking about your optical sensor solution suggestion earlier in my design brainstorming.The question is, if I position a sensor to measure the temperature of the air inside the chamber, would it somehow give me enough feedback about the temperature of the surface of the bread itself? Somehow the bread and butter scientists have succeeded in this with a toaster oven.I don't see any practical way to possibly point an IR thermometer directly at the toast surface because the heating elements are completely and closely positioned near both sides of each slice of toast like bookends. There is no room for placing any IR sensor between the heating element structures and the toast, nor could a sensor be protected from heat sufficient to fry an IR sensor. Further any heat sensor facing the bread surface could easily foul the movement of the toast holders and other mechanical components, be exposed directly to the heat from the heating wires, not to mention the likely easy fouling of the sensor window surface by the toast dander itself. If I chose to mount the IR sensor outside of the chamber facing the bread surfaces, the sensor would have to peek through the mica sheets supporting the glowing heater wires to have a view of the surface of the toast. A second sensor would be required for the other slice of toast.

author: Beeper
author_rank: Contributor
timestamp: November 08, 2014, 03:29:47 am
content: In my absence, the original 555-based toasted decided to fail.Not willing one day to be without her morning toast, my girlfriend wouldn't even bother to call me before she went out and bought a brand-new Philips toaster for $60 that supported some new and novel toasting features not found on the old one.She was very surprised to discover that the new toaster unevenly toasted one side of the toast much more than the other. She had to promptly return it for a refund. I was called and volunteered to make a repair of the ailing old toaster. I am sure her old toaster is truly a jewel among appliances and it was more than 10-years old before it had any problem.In the meantime, my girlfriend is making terrible toast with a cheap open top grill, a type of flat-bed grill that has three quartz elements to provide a great deal of uneven heating yet glow with a beautiful orange-red color. It ends up mostly heating the kitchen room itself in operation. She has to manually turn over the toast and watch it carefully to not burn, even though it has a charming blue-LED backlit LCD screen and precise MCU timer that will allow up to 4 1/2 minutes of operation, but it has no temperature control. It ultimately yields a dessicated result. If one attempts to repeat the process with a second set of slices, it has a thermal cutout that usually terminates any further toasting progress for several minutes before it resets. I guess its function is to protect the LCD and microprocessor from over heating from heat conducted through the case to the control PCB from the heating elements.So I must hurry to finish this project!

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 08, 2014, 07:10:09 am
content: These guys (well SensAbility) are already trying to commercialise their product I believehttp://www.applidyne.com.au/ckfinder/userfiles/images/Article%20The%20Advertiser%20Wednesday%208%20January%202014%20-%20SensAbility%20Toaster.jpg

author: Paul Price
author_rank: Super Contributor
timestamp: November 08, 2014, 07:40:21 am
content: The Aussie article was sent to press exactly 11-months ago. Where's the toaster? Looks like they are using four separate heating elements from the marks on the toast, that isexcept for the one that is being eatenby one of these blokes.They've probably don't trust eating the toast they've created.I'd bet they ran out of bread by now.$50,000 Aussie doesn't go that far, not with three cooks in the kitchen..I would guess their startup might be toast by now.On the other hand, Beeper could take his toaster hack idea to a crowd-funding website and make some dough!

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 08, 2014, 08:05:09 am
content: I didn't actually look at the date of the article. Wouldn't be surprised if it didn't go far (due to lack of funds or lack of market).

author: GreyWoolfe
author_rank: Unknown
timestamp: November 08, 2014, 02:19:21 pm
content: Quote from: Bored@Work on November 07, 2014, 06:57:52 amRube Goldberg must be smiling down on this thread.

author: Beeper
author_rank: Contributor
timestamp: November 10, 2014, 12:21:38 am
content: GrayWoolfe:Rube Goldberg tried to find the most ridiculous, complicated, time-wasteful and unneeded steps to find a way to humorously accomplish some mundane task.Consider this: Peace and quiet in the marriage - PricelessCost to get up and turn off the TV or change the channel by hand : $00.00Remote Control to do the same a million times when desired: $10.00Possible Rube Goldberg Solution:Release a mouse that waits to get hungry and travels across the room to get a piece of cheese on a trigger switch that causes a spring to shoot a football into the air that hits a lever to..... etc etc etc.. (2-minutes later)..to get gun-fired marbles that are directed towards the channel or on/off switch on the TV to finish this same task.Or this:How many tons of bread discarded each day by individuals throughout the world after being burnt by some toaster screw-up?The Rube Goldberg Result of Burnt Toast in the Morning: (Or the story: The Straw that Broke the Camel's Back)A piece of burnt toast during a hurried breakfast sparks an unnecessary argument in the morning between a couple: On the way to work the man is tired, hungry and irritated by this trivial argument, gets in a verbal fight with his boss. He is fired, on his way home his car gives him trouble, walking home he is accosted by a street person and ends up killing him and an innocent bystander nearby...(Didn't Michael Douglas make a film like this?)

author: Macbeth
author_rank: Super Contributor
timestamp: November 10, 2014, 12:39:42 am
content: The inner skinflint in me never discards burnt toast. I simply scrape the excess carbon into the bin, then proceed as normal with the butter.Also, toasting hippy vegan breads full of seeds and grains and other rubbish. Sorry - but the organic artisan bread maybe almost edible when spread raw with vegan soya paste spread, but as soon as it has merely seen a flame it turns into cardboard (especially those seeded breads). I do like granary bread as is, but they are rubbish for toast compared to plain old white thick sliced to fit in the toaster.

author: Beeper
author_rank: Contributor
timestamp: November 10, 2014, 07:33:02 am
content: Update:I've just purchased a $20 US consumer oven thermometer that is spec'd on the package to be usable from 0 to 250-deg C. It's spec'd to be accurate to within a degree or two over its temperature range.The probe is a 2.5mm(approx) diam. stainless steel pointed cylindrical rod approx a little longer than the length of the toaster, with a J-type shape. There is a bend on the j-output side where a stainless steel braided cable emerges from the probe body and a flat-crimp secures the cable. I will add a second probe on the opposite side so the MCU can easily work with double or single-slice situations and because the probe price is really quite low.The probe has a sub-mini-phone plug and the display is a LCD readout that shows a 3-digit temperature reading.The whole thing is powered by a single 1.5 V AAA battery.The length of the stainless steel probe must be bent to to shorten the probe to allow me to insert the probe into the side and position the tip of the probe near the center of the toasting chamber. A second bend is needed to wrap some of the probe's excess length around the outside chamber. I will need to drill just two holes per probe, a hole to insert it and one for a bracket to fix the probe's position. A small piece of spring metal wire will affix the probe body inside the chamber to one of the toast guides( there are several strong stainless wire-thin guides/supports on the toast carriage used to both center the toast in each chamber and keep things away from the heating elements.)Adding a metal temperature probe demands that I have isolated power for my circuit. The old 555 power supply used a tap on the heating wires to create a high-current resistive voltage divider for AC power for the control board.I have small 12VAC CT transformer that fits perfect into the toaster housing but I still may need to use the old 555 P/S circuit with opto-isolation to control the high-current pop-up release solenoid.

author: Beeper
author_rank: Contributor
timestamp: November 10, 2014, 09:09:12 am
content: Unfortunately, an IR optical thermometer on sale was sold out quickly so I have now found another way to calibrate the sensor without it.I have dissembled the oven thermometer's case to get access to the temperature probe's connection to a black-blob MCU on the original PCB.I can get accurate readings off the LCD of the probe's temperature using a hotplate and I can record the voltage presented to the A2D input on the MCU to get a clear DVM reading at the A2D input pin at the probe temperature shown on the LCD screen. I will take several temperature readings and corresponding voltage/thermistor R readings. In this way I can choose to either duplicate the circuit that powers this probe now and just use these probe's temperature v. voltage readings or use the R readings to identify the thermistor used.It is now time to do a web search for a hi-temp standard thermistor temp. v. R chart that will match my readings.Either way I will quickly find a way to calibrate this probe to work with my MCU.

author: Beeper
author_rank: Contributor
timestamp: November 10, 2014, 07:19:50 pm
content: I am still quite amazed by the extra engineering thought that certainly went into the mechanical and electrical design of this fine toaster. Toasting bread is not so easy to accomplish consistently with variations in toaster, bread, and room temperature.I just noticed that the designers have created vent-holes on the bottom of the toasting chamber to ensure an air draft.Perhaps this air draft-effect creates a more uniform air flow and thus uniform heating and toasting at or near the critical toasting temperature?Perhaps helps to remove moisture from the toast as it is evaporated?Serves to help stop heat buildup inside the toaster that would cause shortening of toasting times with increasing toaster temperature?Is it just that the thermistor hanging over the edge of the old circuit PCB compensates for heat buildup inside the toaster that would shorten the next toasting time because if the toaster chamber is already hot, any new toast inserted warms faster?Or else to compensate for temperature changes inside the toaster that causes drift in the 1-meg browness/timer pot resistance and also drift in the electrolytic cap used to set the 555-timer toasting time?Or all of the above?

author: Macbeth
author_rank: Super Contributor
timestamp: November 10, 2014, 11:40:24 pm
content: Quote from: Beeper on November 10, 2014, 07:19:50 pmErm... the "vent holes" below are for releasing all the crumbs in the crumb tray below. I do hope you empty your toasters crumb tray every so often?

author: miguelvp
author_rank: Super Contributor
timestamp: November 13, 2014, 03:10:02 am
content: Quote from: 3roomlab on November 13, 2014, 02:48:02 amSelfie toaster, but it's based on a metal plate that already has the cutouts from a picture you provide them. My wife got one for my daughter, I think I already mentioned it.Edit: then again, using lasers will be cooler, using a couple of speaker coils to move a mirror to paint a 2D picture

author: Macbeth
author_rank: Super Contributor
timestamp: November 13, 2014, 04:02:04 am
content: Hmm... I just had two delicous pieces of toast, slathered in butter at just the right temperature so that little islands of solid butter were to be enjoyed and the bread was not soaked. Toast Heaven.I just noticed the Aldi has a glass fronted toasterhttps://www.aldi.co.uk/en/specialbuys/thursday-13-november/product-detail/ps/p/glass-toaster/for only £29.99Considering it is not just getting the toast perfect, but also eating it as soon as it is at the ideal temperature, I think all these fanciful electronic toast gauges are futile. There is certainly science involved in making a good toast, but I would say a certain art is involved too as all good engineers know!The glass toaster looks far more practical to me. I mean I will be cooking bacon and eggs or boiling a kettle for tea anyway.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 13, 2014, 04:21:41 am
content: Maybe an array of small halogen lamps can be used as a printer of sorts? The laser idea also sounds interesting. Scan a line across the bread while pulsing the laser like in a laser printer and sense the reflectivity to get just the right darkness in a given spot, then move the bread to do the next line.

author: Beeper
author_rank: Contributor
timestamp: November 13, 2014, 05:49:58 pm
content: Macbeth, there is a large area removable tray that sits on the bottom of the toaster directly underneath the toasting area that collects crumbs, so the vents I mention are there for another purpose.Alas, there is no Aldi toaster nor Aldi nearby, but this is my project, I will not settle for some Aldi immodest toaster.I am making perfect toast in the name of science!I can already just use the cancel button on my toaster tp repeatedly pop up and restart toasting so I can closely monitor the progress of toasting if I chose to, I am not going to babysit my toaster every second through a toast session while I have a breakfast to make and a morning paper to read!Besides, look at the size of this thing, it is far too long to fit anywhere in the kitchen. Even the old toaster was sitting very near to fall off the edge of a kitchen cabinet top because of lack of room.

author: Beeper
author_rank: Contributor
timestamp: November 13, 2014, 06:18:29 pm
content: I have two thin thermistor probes now installed where the thin metal stop brackets for the toast carriage were mounted to. The probes are now the stop that limits the depth the toast carriage can descend to.Consider the thermal dynamics of these probes v. my goal of detecting the point of perfect toasting:Since the two probes need to detect when the surface of the bread reaches the magic browning temperature to time the thermal dose to achieve perfect toast, will these probes give me the temperature feedback needed?The probe tips must be safely positioned out of the way, the only suitable spot was to position the probe tips near the center of the length of the toasting chamber, between the bottom of the bread toasting carriage and the bottom unused area of the toasting chamber. Yet the probes are targets of the bookend mica sheets holding the heating elements and chamber's moving hot air.They are also made of reflective shiny stainless-steel and reflect some heat, but also they are metal and conduct some small amount of the probe's heat outside of the chamber.They're positioned in the heating area of the chamber just below the bottom of the metal toasting carriage that the bottom of the toast sits on, so they are also exposed to the approx. 15% of the toasting wire's radiant heat and are certainly immersed in the heated air flowing in the toasting chamber.What is the result?a)Is it that he surface temperature of the toast could only be determined by an optical temperature IC(before mentioned) looking straight at the surface, while my probe temperatures are derived temperature readings, they are not proportional feedback of surface temperature for the MCU to work with, even if their location is very nearby the surface of the toast?b)Or is it that the probes themselves are between the elements and the toast and so are being heated by heating element radiant heat, so they are hotter than the toast and the probe temperature reading does not relate well to toast surface temperature?c)Or is it that the probes are immersed in slow-venting hot air rising towards the top of the toaster and are therefore sensing the temperature of the same air heating/cooling the surface of the toast, and this reading is close to sensing toast surface temperature by an optical sensor, so even if toast surface temperature might largely be due to to radiant heat, my probe readings yields a temperature reading proportionally accurate enough for a MCU to make perfect toast?d)Or since it is well-known that toast will not burn below a critical browning temperature, that the use of a MCU with temperature sensing feedback can always limit toasting chamber temperature to a safe value, thereby preventing burning of toast, even if the result is not perfect toast, but dessicated and quite edible crouton stock.

author: Macbeth
author_rank: Super Contributor
timestamp: November 14, 2014, 12:47:56 am
content: Well, what can I say, I discovered an ozzie website that provides more details on the glass toasterkuchef.com.au... It can take 36mm wide pieces of bread, or crumpets, English muffins, bagels, whatever you throw at it. The width means you can slice a loaf sideways and make a mega toast!I'm sold. Will pick one up tomorrow (I have an ALDI on my doorstep).Good luck, sir, on your scientific toast quest. I maintain that there is more of an art at making great toast than a perfect science, but godspeed!

author: Beeper
author_rank: Contributor
timestamp: November 14, 2014, 03:02:35 am
content: Macbeth: make sure you unplug the toaster if you leave the room!User Manual says"Do not leave the toaster unattended while in use. Disconnect itfrom the power supply when you are finished with it or when leaving the room."

author: Macbeth
author_rank: Super Contributor
timestamp: November 14, 2014, 03:12:25 am
content: Quote from: Beeper on November 14, 2014, 03:02:35 amGor Blimey! I guess I will have to stick with the shitty toaster my dad found thrown away on a skip instead. Thank you for that life saving advice, I don't know how to repay you.

author: tom66
author_rank: Super Contributor
timestamp: November 14, 2014, 09:49:29 am
content: Most of my toasters have that disclaimer. They also say not to leave toast unattended while toasting.

author: PointyOintment
author_rank: Frequent Contributor
timestamp: November 15, 2014, 11:23:22 pm
content: Quote from: Macbeth on November 14, 2014, 03:12:25 amHook it up to a PowerSwitch Tail or other relay connected to a PIR sensor to automatically disconnect it when you leave the room!@Beeper: Consider that the toast may continue to toast due to its own heat after the heating elements have been turned off. I don't think this effect is likely to be as significant with toast as it is with other (higher specific heat capacity) foods such as eggs, though. However, if you want to measure it, you will need to toast several toasts to different toastednesses and measure their heat capacities with a calorimeter, and then fit a curve to get a function which you can integrate to find the final toastedness resulting from turning off the heat at a particular toastedness level. Also, consider that you can probably use the heating elements' resistance to sense their temperature, which may be useful for fine regulation—I assume they already use that effect for coarse regulation the same way incandescent lightbulbs do.

author: Psi
author_rank: Super Contributor
timestamp: November 16, 2014, 12:03:53 am
content: You should buy a solder paste reflow oven and modify it to toast bread

author: Beeper
author_rank: Contributor
timestamp: November 16, 2014, 05:02:13 pm
content: PointyOintment,The way post-cooking of toast is prevented in a toaster is clearly the clever ejection action when the toasting cycle is completed. Once the toast is ejected, no problem!My strategy to achieve perfect toast is to heat whatever is to be toasted to the critical browning temperature, (toasting timer starts)hold that temperature with PWM control until the exact browning time dose has expired, then immediately eject the toast out of overtoast danger by the magic of "Pop-Up." My toaster literally tosses the toast out of the toaster, not just pops-up.Update: I am wiring together a breadboard with MCU probe sensor interface and TRIAC PWM control and writing PIC C-code to boot(toast).PSI, I will soon try my luck at SMD PCB's and this toaster to just toast work should provide the way to fuel my body with a mountain of peanut butter and toast to give me the energy to work on modifying a toaster-oven for SMD work. Fortunately, there are already many who've posted on this SMD solder-melting topic.

author: michael.hill
author_rank: Unknown
timestamp: November 18, 2014, 04:17:24 am
content: Don't forget to add a special switch for bagel toasting, which, traditionally is only toasted on 1 side. (Actually, sliced bread was also originally toasted on just one side as well, but that's another thread in its own right.). You could also approach toast how I approach roasting a turkey. Cook it somewhat slow to start with to cook the inside, then raise the temperature to a blazing hot 450-500 F. Perhaps the very fundamentals of toast making and toast making culture should be reconsidered. I am going to propose starting off at a lower temperature and ramping it up after it it is at a sufficient temperature. The final texture should be slightly chewy on the inside, but a golden crisp on the outside with a gradient of textures. This would be akin to a well-prepared scallop or steak, where the gradient of doneness is essential to the dining experience.Just a thought.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: November 18, 2014, 11:08:03 pm
content: A sideways thought!My Grandmother had a fridge powered by gas which seemed crazy. It took some time for me to work out how it worked - I wasn't even in double figures at the time but the library helped.I still think that kitchens should be monolithic in the sense that there could be a lot more exchange of heat. I'm not enough of an engineer to work it out though. I'm just convinced that it should be economically possible.Any thoughts?

author: Beeper
author_rank: Contributor
timestamp: November 19, 2014, 12:16:58 am
content: David Turner,The toaster does it's part in heat exchange. On a cold morning it it does a little to warm the kitchen and it is a nice hand-warmer as well all the while making toast.While heat exchange things might be economically possible they also might be practically and aesthetically undesirable, like toasting bagels in a toaster. Somethings are done and have a bad taste and somethings are done in bad taste.Michael.hill, we use the open-top flat-bed toaster (as described in my previous comments) for bagels, they are just too thick to fit in the toaster, too easy to get caught in it's works, and really, just one side is desired to be toasted.The denizens of Macbethland's north have the right idea for bread products of all types, they do not worry about fat exchange more than heat exchange, it suits them well to just fry their bread in a sizzling puddle of sausage fat.