I received this email today from Boaz Shuval, a fermentation experimentalist in Israel, about a fascinating experiment he tried:
One of my favorite fermentations is yogurt making, and I’ve been making my own since 2005. For years I have been using commercial yogurt cultures as starters, and have had to replenish them every few generations. In your book you mentioned the heirloom yogurt cultures, which intrigued me. Unfortunately, the commercial sources of heirloom yogurt cultures do not ship to Israel, where I live. Nor do I know anyone who has an heirloom yogurt culture here in Israel. Therefore, it was with great interest that I read the chapter [in The Art of Fermentation] about plant origins of yogurt.You mentioned a great deal of possible natural sources for yogurt cultures, some of which, like ant eggs, I was not keen on trying. However, you did mention that in India chili-pepper stems may be used as a source for yogurt cultures. This was something I was willing to try. So, I bought a package of red chili peppers from the store. I heated one liter of whole milk to 180F, and let it cool gradually to 110F (I let it cool slowly, over 2-3 hours). I briefly rinsed the chili peppers, and cut the stems off a dozen. I place the stems in a container, and added the milk. I placed that in my yogurt incubator. After 10 hours, nothing had happened. I decided to let it continue fermenting. After about 13 hours, the magic happened, and the milk had gelled! In fact, it had over-fermented a bit, and split. I had a layer of whey at the bottom, on top of which floated a very thick curd. I cooled it in the fridge, and it tasted like spicy, chili-flavored yogurt. I used one teaspoon of this yogurt to inoculate a fresh batch of milk.Again, I repeated the same process: heat to 180F, cool to 110F, incubate at 110F-115F. The yogurt set beautifully after about three hours. This is a really fast-setting yogurt culture. The result was a very thick yogurt (this time I stopped the heat on time, so it did not split). I should probably say that it is a yogurt-like product as I don’t actually know what’s in it. Flavor-wise, it tasted very good. It is quite sweet and not very acidic, even thought its pH level does go down to 3.5-4 (I used a pH strip to test).This yogurt culture so far has reliably made 5 generations of yogurt. My routine now begin at about 6:00 PM, where I heat up my yogurt. I then let it cool gradually over three hours. If, at 9:00 PM, it has cooled too much, I will heat it a little to raise the temperature to 110F. I add a teaspoon of yogurt culture from the previous batch (this I remove after the initial cooling of the yogurt and set aside). I incubate at 110F-115F for three hours, until midnight. By this time, the yogurt has begun to gel, although the gel is quite fragile. I kill the heat from my incubator at this point, and keep it insulated until the morning. By morning time, the yogurt will have beautifully set into a firm curd, and be just slightly warmer than room temperature. I then refrigerate it for several hours, where it continues to firm.I am very excited about this. Naturally, I was very doubtful that this would even work. I have been sharing it with whomever would listen. I have also given some culture to a friend. I wanted to share this with you, so you could share it with more people than I can. It also makes me wonder what other sources of plants are used to make yogurt. Perhaps different plants can make different flavors and consistencies of yogurt? If you know of some information on the matter, I would greatly appreciate it if you could share it with me.Thank you again for writing your fabulous new book. It is indeed a fantastic source, possibly the best source, of information about fermentation. It has been the source for many fermentation experiments at my home.Best,Boaz
All the (fragmentary) information I know related to this topic is in The Art of Fermentation, plus the experience described in this email. If others have experience with plants as a means of culturing milk, please post here as a response.