Introduction: Color-Changing Cocktails. Blue foods are striking (and rare) all by themselves, but add a little lime juice and this emerald blue elixir will *magically* change into a brilliant purple. I've named my little cocktail the Indigo Blush. The intense color is completely natural (from a flower!) it's not difficult to make, and the color transformation is truly stunning. The basil/lime/gin flavor combination is bright, refreshing, and dangerously drinkable.  If you're impatient and just want the recipe, go ahead and skip to the last step. Read on for my full, exhaustive treatise on color-changing foods. Some recipes start from an idea and just magically come together when the ingredients are in my hands. Others take years of fiddling, research, scrapping the whole idea and starting again, more fiddling, seeking expert advise,  testing and retesting before satisfying results emerge. This recipe is definitely in the latter group. The idea of a color-changing recipe is one of those white whales I have been chasing for years, and finally, I have a dish I'm excited to share.  When I first read about color changing food pigments I could barely contain my glee. I mean, think of the possibilities: a dish that can change COLORS? It turns out that lots of plants have pigment molecules that are pH indicators. In a neutral or basic solution they will appear green-blue or blue-purple, but add some acid and they'll turn purple or red. (You've probably seen examples of this already: blueberries in blueberry pancakes will sometimes turn green if the batter has too much baking soda, or brush your teeth with a baking soda toothpaste after drinking a glass of red wine and you'll end up with a mouthful of blue foam.)  Lots of dishes get a little something acidic thrown in at the end, so it didn't seem like making a dish to use this color-change trick would be too difficult. My very first experiments quickly showed that I would need a mostly clear solution in order to show off the color change. (Opaque foods just muddied it up and got in the way). So I got to work trying out all sorts of ingredients with color-changing pigments: radicchio, red cabbage, blueberries. The findings of these tests were disappointing. Either the color would come out muddied and dull (blueberries) or the flavor would be horrid (red cabbage) or both (radicchio). And that's not even getting to the hardest part: acidity. Nearly everything that we eat is acidic. Egg whites and most tap water are slightly basic, but everything else is just varying degrees of acidity. For the color change to work, you need an acid addition that will significantly change the pH, but not until the dish is served. (So adding any acid to the mix beforehand is a no-go.) And this makes adding any flavor difficult. Just about every flavor-enhancing technique I thought of either muddied up the color or added acid. Perhaps, I thought, this is a phenomenon that works great in an eighth grade chemistry class, but really shouldn't be brought into the kitchen. And then I met this little blue flower. (Hello, butterfly blue pea flower!) It doesn't seem to have much of an audience in the US yet, but Thai and Chinese cooks have long used this little flower to color foods and make teas with a brilliant blue hue. For my money, this is truly a remarkable ingredient. For one thing, it's hard to overstate how brilliant the color from this flower is. The pigment is highly soluble-- you don't even have to boil it to release the color. And since the flowers can be dried, it is easy to keep them on hand. The only slight detractor is that they don't have any real flavor on their own. But even that negative can be a boon-- you could use these little guys to color any sort of dish, and add whatever flavors you want separately. Finally I had an ideal candidate to make a color-changing recipe, and I decided a fancy cocktail would be just the thing to showcase this remarkable little ingredient. I chose to make an alcoholic beverage, but there is no reason that the same techniques wouldn't work for non-alcoholic beverages.  Step 1: The "Secret" Ingredient. The first (and most difficult) part of making this drink will be getting your hands on some butterfly blue pea flowers. (Unless you happen to live in Thailand. Then it seems like it will be quite easy.) I have found the easiest way to get these guys is to order through amazon. Search for butterfly blue pea flowers in tea, and you'll find a few vendors that carry them. The catch is, they all ship from Thailand, and shipping to the US usually takes about a month. They aren't cheap (with shipping my order was around 20$), but the 50g. bag that I bought will definitely make around 5 bottles of color-changing liquor. And the dried flowers keep well, so you could get quite a lot of use out of an order.  While it isn't easy to get your hands on dried flowers in the US, it is fairly easy to get seeds. So the other option is to grow the plant yourself. I was so intrigued by this little flower, I decided to try my hand at growing some fresh ones in my backyard this year. I am by no means an expert gardener, but I can share a few tips that I've figured out from growing this little guy. (And, if we're being honest,  killing off some other seedlings along the way) 1. Use a bean/pea innoculant when you start your seeds. I tried germinating two batches of seeds, one with innoculant and one without. I got a MUCH better germination rate (around 70%) with innoculant as compared to 33% without. 2. Heat, heat, heat. Unlike regular garden peas, these guys like it hot. I started some seedlings on a heating mat, which seemed to work. But my attempts to harden off plants to grow outside in colder temperatures (60-70s F) were not successful. The healthy plant that I grew was started indoors with lots of light, and I didn't move it outdoors until the temperature lows were in the 70s (mid-summer here in New York). You also want to plant them in well-drained soil, and don't over-water them. (This plant likes soil on the dry side.) 3. This plant has delicate roots and does not like being repotted. I would suggest starting seedlings in peat pots so you don't need to disturb the roots when transferring them to a container or the ground. 4. Give them a trellis or fence to climb on. Like other varieties of peas, this plant only seems to flower once it has reached a certain height. (Then the extending vines produce lots of flowers. ) 5. If you want to have enough blossoms to make a bottle of color-changing gin, you'll probably need several plants. I'm estimating that my single vine will produce about 2 dozen blossoms this year. That's not bad, but it would only make about a quarter of a bottle of liquor. The plants really are stunning, though. And the fresh flowers can be eaten and used as a garnish on all sorts of dishes. I'll definitely be planting them again next year.  Step 2: Elements of a Color-Changing Cocktail. To create a color-changing cocktail I knew I would need a butterfly blue pea-infused liquor, and then an acidic addition to activate the color change. I also wanted to add some other flavors and a little sweetness to the cocktail. After a little poking around, I found out that most vodkas and gins have a neutral or near-neutral pH. I chose gin for my cocktail, but vodka would work just as well.  Adding other flavors gets a little tricky-- it's hard to add anything into the mix without inadvertently adding acid. (And we want to save that for the dramatic finale.) I found that creating a syrup with fresh herbs did not add too much acidity, and could still bring lots of flavor with them. I chose to make a light syrup, (not that high of a sugar concentration) just because I don't like my drinks very sweet. I was going for flavor, with just enough sweetness to cut the harshness of the gin and balance the acid addition. I also found that infusing a hot syrup gently (rather than boiling it) will give you a syrup that is more clear. It's not totally colorless, but it's clear enough so the color-changing effect isn't noticeably diminished. The last element was the acid. I tried a number of combinations of floral and herbal syrups with different acids (including some interesting experiments with white balsamic vinegar and vermouth.) The clear favorite in the taste category was basil syrup with fresh lime juice. I'm sure that there are other winning combinations out there-- I anxiously await to hear more ideas from all you talented mixologists... The one caveat I would add is that you get the most dramatic color change effect when you add a strong, liquid acid. (I did some tests with powdered citric acid and frozen lime juice: meh.) The most satisfying display was with just plain lime juice. I specify straining the lime juice to try to keep the drink as clear as possible. Step 3: The Indigo Blush (My Recipe for a Color-Changing Cocktail). Indigo Blush: 2 oz. Blue Gin 1 oz. Basil Lemongrass Syrup 1 oz. Strained Lime JuiceBlue Gin: ½ bottle dry gin 3-4 T dried butterfly blue pea flowers baking sodaBasil Syrup: 1 c. sugar 1 ½c. thai basil (If you cannot get thai basil, just use italian basil and add 1-2 seeds of star anise. And just one prong off the star, not the whole thing.) 2 T sliced lemongrass 2 c. boiling waterFor Serving: Limes (1 oz. lime juice per serving) Fine-meshed strainer tea pot, creamer or other container to pour a small amount of lime juice into the finished drink. IceInfuse Gin One at a time, remove the green base leaves from the dried flowers, keeping just the colorful petals. Place the petals in a clean jar and cover with gin. You don’t need to fill the jar up, just enough to cover the flowers.  Stir to saturate the petals. Once they are softened, you can crush them lightly against the side of the jar. This will help speed up the dispersal of the color into the gin. Leave the mixture to sit for a day or two, until it turns very dark blue-purple. Strain out the petals and pour the concentrated color into a clean bottle. Pour in additional gin until it is diluted to your desired color intensity (remembering that the color will be dispersed more when it is mixed into a cocktail.) Most likely, the bottle of gin will have a purplish hue at this point. Add a ât. baking soda to the gin and shake to disperse. You can add more baking soda if it is necessary to nudge your gin into the blue range of the spectrum. But go slowly, and add just enough to get the job done. Add just a little and you'll never know it's there, but too much baking soda tastes terrible.  The color tends to have a more purple appearance when you look through a greater depth. So hold the bottle to the side and look at the color of the gin at the edges to get a more accurate idea of what your gin will look like when it is poured into a cocktail. The infused gin can be made well in advance-- my color infused liquors have shown no signs of losing their brilliance after several weeks. (I'll update if there is any change in the shelf life of the colored gin, but the color seems quite stable.)Make Syrup Remove basil leaves from the stems and wash. Slice lemongrass as finely as you can. Lightly bruise the lemongrass under the flat side of your knife. Place sugar, lemongrass and basil leaves (and star anise, if you are using it) in a heat resistant container. Pour  in 2c. boiling water and stir to dissolve. Cover the container and let it steep for several hours, until the mixture has cooled to room temperature.  Strain the syrup and refrigerate. (Refrigerated syrup will keep for up to two weeks.)Mix Cocktail Juice a few limes and pour the juice through a fine-meshed tea strainer or coffee filter. You want this liquid to be as clear as possible to give the finished cocktail its gem-like brilliance.  Measure two ounces of blue gin and one ounce of syrup. Is the color still a nice blue? If so, just charge ahead. If it has edged towards the purple spectrum with the addition of the syrup, you might need to add just a pinch of baking soda to push the pH back toward neutral. Again, go slow, and make sure not to overdo the baking soda. Shake in a cocktail shaker and pour into a martini glass. To complete the cocktail slowly pour 1 oz. of strained lime juice into the glass. (This would be the recommended moment to stop for a few minutes to bask in the the oohs and ahs.)Tips for Cocktail Brilliance. Since the color is the star of this show, it really pays to have a white background. (It is much harder to see the color change against a dark background or competing colors.) A white tablecloth or plate underneath the drinks works wonders. If you have enough flowers, you can make the drink as intensely blue as you want. BUT I find that you lose some of the brilliance of the color if it is very highly concentrated. When the drink changes colors it will also appear to lighten. So expect that your finished purple drink will look lighter than the initial blue base.