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.