Abstract:
The freshness of fresh brewed coffee is extended by adding an antioxidant to the coffee during the brewing process. The antioxidant may be added to the coffee grinds in the hopper, directly into the pot, or may be impregnated into a disposable paper filter fitted into the hopper to retain the grinds.

Description:
The present application is a continuation-in-part of an application filed Jan. 28, 1999 and assigned Ser. No. 09/238,993, and the present invention relates to a method and apparatus for monitoring the freshness of fresh brewed coffee and for providing a readout of the freshness on a suitable display. 
    
    
     BACKGROUND OF THE INVENTION 
     Coffee is a beverage that has a taste and aroma which is more desirable when it is fresh than when it is older and “stale.” This is because the compounds which contribute flavor to the coffee are organic in nature and the flavor is the most desirable immediately after the coffee is brewed because the compounds which impart the flavor have not degraded. Over a period of time the organic compounds of the coffee oxidize by combining with oxygen in the water from which the coffee is brewed and the oxidation results in the degradation of the coffee and the loss of the desirable flavor. 
     There are numerous brands and types of coffees available, and coffee can be brewed such that it is “strong ” or “weak ” or to any intermediate strength. Individuals who regularly drink coffee desire that the brew have a “strength ” and level of “freshness ” which is satisfactory to their own palate, and therefore the strength and the freshness of coffee are critical variables to connoisseurs of coffee. 
     One who makes a pot of coffee may grind or purchase his choices of coffee grinds and place those grinds within the hopper of a coffee maker. Hot water is either percolated through the grinds or it may flow from a reservoir above the hopper through the grinds to a removable coffeepot below the hopper. The degradation of the coffee commences as the pot is filling with coffee and proceeds at a rate that may vary depending on the type of coffee and the degree of the grinding. 
     In our previous U.S. Pat. No. 5,724,882, we disclosed a coffee maker having an optical feedback system in which a red light from an LED was directed through a transparent coffee pot and the intensity of the light passing through the liquid was monitored to make a brew having a predetermined concentration. U.S. Pat. No. 5,724,882, therefore, disclosed a method and apparatus for brewing coffee to a predetermined strength. Coffee from a coffee maker in accordance with our prior invention will nonetheless become stale over time, and a connoisseur of coffee employing such a coffee maker could not ascertain whether the coffee has become too stale for his palate without tasting it. It would be desirable, therefore, to provide a coffee maker which would brew coffee at a desirable concentration or strength and which would also provide a readout of the freshness of the brew remaining in the pot. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention is embodied in a coffee maker having a hopper for retaining coffee grinds from which coffee would be brewed and having a heating element below the hopper having a generally planar upper surface for receiving a coffeepot. The coffee maker further includes a source of hot water, which may be a heated reservoir positioned above the hopper and a control valve for controlling the flow of hot water from the reservoir through the coffee grinds and into the pot on the heating element below. 
     In accordance with the invention, the pot is transparent and the device further includes a light source or LED for providing a beam of light having wavelengths in the ultra violet, visible, or near infrared range which is directed through the lower portion of the coffee pot to a photodetector on the opposite side of the coffee pot. The device further includes a circuit for measuring the intensity of light detected by the photodetector by measuring the voltage output of the photodetector to determine the transmittance of light through the coffee. 
     We have found that the organic components which make up fresh coffee are partially transparent to light waves, especially to red light waves from an LED, but as the organic matter which imparts flavor to the coffee degrades and the coffee brew becomes progressively more stale, the transparency of the brew to the light also progressively decreases. We have found that the voltage output of the photo detector drops at a rate which corresponds to the rate at which the coffee looses its freshness and becomes stale and therefore a display of the downward progression of the voltages from the photo detector is also a display of the deterioration of the freshness of the coffee. 
     In accordance with the invention, the circuitry of the device includes a means for digitally measuring the voltage potential of the LED and storing that voltage in a first register. Subsequent voltage measures are thereafter compared to the first voltage in a first comparator and if the new voltage is larger than the old, replacing the old voltage with the new until a maximum voltage is found. In like manner a second register and a second comparator are used to find a minimum voltage output from the photodetector. The maximum voltage is reached when the coffee has the greatest transmittance to light which occurs at the completion of the brewing of the coffee. The richest coffee having the lowest transmittance is made with the water which first passes through the grinds in the hopper and therefore the first reading from the photodetector, when the level of coffee in the pot is the lowest level covering the photodetector, is taken as a minimum voltage output. 
     The circuit causes the maximum voltage, as recorded in the first register, to be a measure of maximum freshness and the minimum voltage as recorded in the second register to be a measure of minimum freshness or stale coffee. After the brewing of a pot of coffee is complete, the organic matters which impart flavor to the coffee gradually oxidize and the brew becomes less transparent to light. As this occurs, the voltage output of the photodetector drops from the maximum, as recorded in the first register, toward the minimum as recorded in the second register. As the voltage output falls towards the minimum, the brew is becoming stale. A LED bar graph may be employed as a display of freshness in which all ten LED &#39;s are illuminated when the coffee is “fresh ” and progressively fewer LED &#39;s are illuminated as the coffee becomes progressively more “stale.”As explained in our patent U.S. Pat. No. 5,724,882, we have previously found that the transmittance of light through the organic compounds which impart flavor to fresh brewed coffee is at a maximum in the range between 600 nm and 1,400 nm. Fresh coffee is partially transparent to light within this range with the absorption of light being directly proportional to the amount of organic matter which imparts flavor to the coffee. Degradation of the organic matter will result in decreased transmittance of light through the coffee within this wavelength range. 
     We have also found that the freshness of fresh brewed coffee can be extended by adding an antioxidant to the coffee grinds or to the water in the reservoir. This may be accomplished in any of a number of ways including depositing an antioxidant within, or on the surface of, a filter used to retain coffee grinds in a hopper. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better and more complete understanding of the present invention will be had after reading of the following detailed description taken in conjunction with the following drawings wherein: 
     FIG. 1 is a schematic drawing of a coffee maker in accordance with the present invention; 
     FIG. 2 is a graph of the optical transmission of coffee after brewing; 
     FIG. 3 is a graph of the output voltage of the photodetector employed in the present invention as coffee is brewed in the pot and then becomes progressively more stale; 
     FIG. 4 is a block diagram of a circuit for use with the device of FIG. 1; 
     FIG. 5 is a schematic drawing of a coffee maker in accordance with a second embodiment of the invention; and 
     FIG. 6 is a cross sectional view of a coffee filter in accordance with an alternate embodiment of the invention; 
     FIG. 7 is an enlarged, fragmentary cross section view of a modification of the embodiment shown in FIG. 6; and 
     FIG. 8 is an enlarged fragmentary cross sectional view of a second modification of the embodiment shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 the coffee maker  10  in accordance with the present invention includes a source  12  of hot water which may be a reservoir having a heater line, not shown, and an output line having a valve  14  therein for controlling the flow of hot water from the source  12 . Hot water from the reservoir  12  enters a hopper  16  of the type having a porous bottom and nonporous sides for retaining coffee grinds therein and below the hopper  16  is a coffee pot  18  made of transparent material such as glass. Below the coffee pot  18  is a warming plate  20  for maintaining the coffee at a desirable temperature. Positioned at one side of the coffee pot  18  is a light source  22 . The invention can employ light of any wavelength which is at least partially transmittable through coffee, but a red LED having a wavelength of 680 nm falls within the range in which coffee has a maximum transmittance to light, that being between 600 nm and 1,400 nm, and red LED &#39;s emitting a wave length of 680 nm are readily available. 
     Referring to FIGS. 1 and 4, on the opposite side of the coffee pot  18  is a photodetector  24  for detecting the intensity of red light from the LED  22  which passes through the liquid in the bottom of the coffee pot  18 . The voltage output of the photodetector  24  is read by a circuit  26  having a logic  27  which may be a microprocessor. The circuit  26  has an output directed to a suitable control device  28 , such as a solenoid, for controlling the opening and closing of the valve  14  and thereby regulating the flow of water from the source  12  through the grinds  30  in the hopper  16 , and through the porous bottom of the hopper and into the pot  18 . In the preferred embodiment the circuit  26  includes the circuitry previously disclosed in our U.S. Pat. No. 5,724,882 whereby the valve  14  may be controlled to brew coffee to a predetermined strength. 
     The circuit  26  further regulates a heat control output  32  for controlling the application of power to the warming plate  20  and a heat sensor  34 , which may be a thermocouple, for providing a feedback to the microprocessor  27  of the temperature of the warming plate  20 . The circuit  26 , therefore, can regulate the temperature at which liquid coffee in the pot  18  is maintained after it has been brewed. The device further includes a strength control  36  whereby the desired strength of the coffee to be brewed may be preset according to our prior patent U.S. Pat. No. 5,724,882 and the device has a freshness indicator  38  which may be a ten LED indicator or any other means which may be employed to indicate the freshness of the coffee within the pot. 
     We found that the transmittance of coffee deteriorates proportionately as its freshness deteriorates. FIG. 2 shows the transmittance of coffee to red light, specifically to light having a wavelength of 680 nm, over an interval of ninety minutes with the zero time corresponding to the transmittance of the fresh brewed coffee. As can be seen, the transmittance of the coffee diminishes as the coffee becomes stale. 
     Referring to FIG. 3 which shows a typical voltage output of a photodetector detecting the intensity of light passing through the bottom of a pot of brewed coffee as a function of time. The output of the photodetector is shown in volts on the vertical scale and time is depicted on the horizontal scale in minutes. The initial voltage reading  39  from the photodetector is very high because the brewing process began with an empty coffee pot  18  which has a higher transmittance than fresh brewed coffee. When rich coffee entered the pot  18  and interrupted the beam of light from the LED  22 , the voltage output from the photodetector  24  dropped to a low point  40 . As the coffee brewing process continued, the coffee grinds produced a progressively weaker coffee which gradually diluted the coffee accumulating in the pot  18 , and the voltage readings from the photodetector slowly rose. In the example shown in FIG. 3, the voltage readout reached its peak at  42  after the ten minutes when the brewing process ended. As the organic material which imparts the flavor to the coffee deteriorated over time, the transmittance of the liquid correspondingly diminished and the photodetector  24  produced a progressively lower output voltage as shown. 
     Eventually, the output voltage from the photodetector will drop to a level which is approximately equal to the minimum voltage reading  40  corresponding to the beginning of the brewing of the coffee. The freshness indicator  38 , shown in FIGS. 1 and 4, depicts the range of the voltage outputs of the photodetector  24  from the maximum output  42  to the minimum output  40  as an indication of the freshness of the coffee through which the light from the LED  22  is being projected. 
     Referring to FIG. 4, we have found that it is desirable to modulate light from the LED  22  and synchronize the photodetector  24  to detect only the modulated light to thereby distinguish light from the source  22  from ambient light. The modulation of the light source  22  will thereby prevent ambient light from interfering with the accurate reading of the device. In the preferred embodiment the light may be modulated at any suitable frequency, such as 1,000 Hz. The circuit  26  therefore includes a modulating circuit  46  of the type known in the art for modulating light from the LED  22  and a synchronous detector circuit  48  such that only the light from the source  22  is being measured. The output voltage from the detector  24  is amplified by an amplifier  50 , and the amplified output is thereafter filtered through a filter  52  to remove undesirable noise, after which the voltage reading is digitized by a converter  54 . 
     The logic  27  includes a peak voltage comparator  56  and a peak voltage register  57  to find and store the peak voltage reading  42  and a minimum voltage comparator  58  and a minimum voltage register  59  to find and store the minimum voltage reading  40 . Voltage readings which follow the peak reading  42  that are higher than the minimum reading  40  are directed to the freshness indicator  38 , which may include a ten level voltage detector  60 , the output of which is directed to a ten bar graph  62 . The peak voltage  42  will cause all ten LED &#39;s to be illuminated as an indication of fresh coffee and the minimum voltage  40  will cause only one LED to be illuminated as an indication of stale coffee. 
     Since coffee becomes stale as a result of oxidation of the organic compounds which impart flavor, the oxidation may be reduced by reducing the temperature at which the coffee is maintained. Accordingly, the freshness of the brew may be maintained longer by employing the heat sensor  34  and heat control  32  to reduce the temperature of the warming plate  20  when the coffee has lost some predetermined degree of freshness to thereby extend the freshness of the coffee. 
     As stated above, the device may further include logic within the microprocessor for controlling the solenoid  28  and the valve  14  to regulate hot water entering the hopper  16  and thereby provide a brew of predetermined strength in accordance with our prior patent U.S. Pat. No. 5,724,882. 
     Second Embodiment 
     The graph of the degradation of coffee freshness as shown in FIG. 3 is typical of most coffees, and a typical pot of coffee can be expected to lose its freshness over a period of 80 to 120 minutes as shown. A simplified embodiment of the invention could, therefore, be constructed as shown in FIG.  5 . 
     In this embodiment a coffee maker  70  includes a reservoir  72 , a valve  74 , a hopper  76 , a pot  78  and a heating element  80 , all in accordance with the prior art. After the reservoir  72  has been filled with water and the hopper  76  filled with coffee grinds the brewing process is commenced by some appropriate means, such as pressing a start button  82 . 
     The device includes a clock  84  for measuring time from the commencement of the brewing process and a freshness display, which may be a ten LED bar indicator  88  in which all the LED &#39;s are illuminated to indicate fresh coffee and one LED is illuminated to indicate stale coffee. A count down circuit  90  allows a fixed interval of time for the brewing of the process to occur, then the circuit  90  illuminates all ten LED &#39;s  88  as an indicate that the coffee is brewed and is fresh. The circuit  90  then turns off the LED &#39;s one at a time with a fixed interval of time, such as ten minutes, between each turn off. After an interval of time, between 80 and 120 minutes, the circuit  90  will have turned off nine of the LED &#39;s so that the indicator  88  will show the coffee as being stale. 
     It should be apparent that the freshness indicator  90  provides only an estimate of the freshness of the coffee and not a measure of coffee freshness as is provided by the first embodiment. 
     Third Embodiment 
     We have also determined that the freshness of coffee may be further extended by the provision of an anti-oxidant to thereby reduce the oxidation of the organic matter which imparts flavor to the coffee. Any of a number of anti-oxidants may be used, and Vitamin C (ascorbic acid) is a suitable anti-oxidant which is readily available. Vitamin C in powdered or tablet form may therefore be added to the grinds in the hopper  16  or to the water in the reservoir  12  such that it is absorbed by the water from the source  12  and enters the coffeepot  18  to extend the freshness of the coffee brewed therein. 
     As can be seen from the graph of the transmittance of coffee shown in FIG. 3, the rate at which the transmittance of the coffee diminished fits a simple exponential decay and can be expressed mathematically as: 
     
       
           I =Io exp  ( −t/t   1/e   
       
     
     Where I is the initial photovoltage and t 1/e  is the time for the photovoltage to decay to 0.3679 of its initial value. 
     When Vitamin C is added to the grinds or the water from which a pot of coffee is brewed, the time constant for the decay is extended. 
     EXAMPLES 
     French Roast coffee beans were ground for 10 seconds and used to make three typical six cup pots of coffee. No vitamin C was added to the first pot, 250 mg of Vitamin C was added to the grinds to make the coffee in the second pot, and 500 mg of vitamin C was added to the grinds to make the coffee in the third pot. The time constants for the decay of the transmittance were then measured and are shown below: 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 French Roast Ground Coffee Sample 
               
             
          
           
               
                   
                   
                 Decay Time 
               
               
                 Pot Number 
                 Vitamin C (mg) 
                 t 1/e  in minutes 
               
               
                   
               
               
                 1 
                  0 
                  42 
               
               
                 2 
                 250 
                 104 
               
               
                 3 
                 500 
                 175 
               
               
                   
               
             
          
         
       
     
     referring again to FIG. 1, according to the third embodiment of the invention the coffee maker  10  of the first embodiment is provided with an antioxidant dispenser  94 . The dispenser  94  is actuated by the circuit  26  to dispense a predetermined dosage of an antioxidant, such as one or two 250 mg tables of Vitamin C into the hopper  16  as shown at the commencement of the brewwing cycle. Alternately, the dispenser  18  could be adapted to dispense an antioxidant into the water in either the reservoir  12  or the pot  18 . The freshness indicator  38  will then display the freshness of the coffee in the pot  18  and will show an extended decay time consistent with the examples above. 
     Referring to FIGS. 1 and 6, an antioxidant may also be added to fresh brewed coffee by impregnating a coffee filter  100  with an antioxidant  102 . The coffee filter  100  is preferably made of paper and is of the type known in the art, sized to fit within the hopper  16  and to retain the grinds  30 . The filter  100  is permeable to water so that water from the reservoir  12  will pass through the grinds  30 , the filter  100  and pores in the bottom of the hopper  16  to reach the pot  18 . 
     To impregnate the filter  100 , an antioxidant such as ascorbic acid and erythordic acid (jointly being Vitamin C) is dissolved in water to reach a saturated solution at about 80 to 100 degrees centigrade. The filter 100 is allowed to absorb the saturated solution until the desired concentration of antioxidant is retained within the filter  100 . As shown in the above table, the absorption of about 125 mg of Vitamin C is sufficient to extend the freshness of a six cup pot of coffee by a factor of two. After the solution has been absorbed by the filter  100 , the water can be removed by subjecting the filter to a short gaseous drying process. 
     As shown in FIG. 7, a coating of antioxidant  104  may be applied to the surface of the body  106  of a filter  108 , or as shown in FIG. 8, an antioxidant capsule or tablet  110  may be retained under a flap  112  to the outer surface of the filter body  114 . 
     It should be appreciated that the antioxidant dispensed by a filter or by the dispenser  94  will change the rate of degradation of the coffee. The simple clock  84  of the second embodiment cannot be used to provide a reasonable estimate of the rate of degradation of coffee to which an antioxidant has been added as described with respect to the third embodiment. 
     Although several embodiments of the invention have been depicted, many modifications and variations can be made without departing from the true spirit and scope of the invention. It is therefore the intent of the following claims to cover all such modifications and variations that come within the true spirit and scope of the invention.