Soy lecithin has proven to be an overwhelming success for my purposes, although now I would like to experiment with how the starting texture, density and acidity of the liquid impacts the size of the bubbles and the ratio of lecithin required.
The drink I am working on is the first of a five course degustation. The foam is a very strong, sweetened hibiscus tea, or tisane really, that will be layered extravagantly over the top of a punch bowl. The punch itself, (peach & fenugreek syrup, white wine vinegar, Star of Bombay Gin, and still water), is a very pale yellow-pink, so the bright pink foam will slowly seep into the drink and colour it. The levels of sweetness need a little tweaking, and a more solid concept of how much foam I would need to produce per serve is required too.
Out of curiosity, I first made a foam with a whole egg white (approx 40mL) and 200mL of the tea, although the foam held excellently, it was far too dense for my purposes. I then made the foam with soy lecithin powder, using 1g to 200mL of tea (a proportion of 0.5%). Pictured below are the foams at least 30 minutes after making. Egg white is on the left and lecithin on the right. At the bottom the two punch glasses show the look of the foam after it’s been in a drinkers hands for a while, again egg white on the left and lecithin on the right. The soy lecithin foam is so much prettier, while the egg white foam has grown clumpy and dry.
I get the idea that perhaps the more acidic a liquid is, the less lecithin is required? The chef tells me he uses just 1g of lecithin to 1000mL liquid to make a foam using vinegar, and he creates large bubbles in that air, so perhaps in my sweetened, low acidity liquid, I can push the proportion of lecithin much higher to achieve the same results. I have more to research, I guess.