Just about everyone who reads a yogurt recipe through for the first time has the same reaction: Wait, you mean I have to BUY yogurt in order to MAKE it from scratch? The answer is yes. BUT…a little of the commercial stuff can be used to make a whole lot of homemade stuff. Up to 20 times more depending on the recipe and how good you are at the yogurt-making process. It works, for all intents and purposes, like a bread starter.
So great then — you might say — if yogurt works like a bread starter then all I need to keep making yogurt forever is to just keep it going from batch to batch. Um, no, not really. The reason for that is because commercial yogurt is more like a mail order San Francisco sourdough starter than a homemade bread starter. Which is to say it will lose its potency and flavor every time you re-use it. Why? Because just like a mail order sourdough starter, commercial yogurt contains microbes that aren’t adapted to living in climates that aren’t their own. After a few batches they’ll be out-competed by whatever happens to live in your area, and your yogurt will get soupier (and probably stranger tasting). So yes, you have to buy and keep buying every so often, or just go pro and buy powdered starter, which works just as well.
All of which begs the question: what’s so special about these creatures? If lactic acid bacteria can be found anywhere, what’s wrong with culturing my own? The answer is that in the same way few (if any) microbes outside of San Francisco can produce enough acid to make a sourdough bread truly sour, few outside of the Asian steppes are capable of making a really good gel. Leave milk out to sour in North America, and the result will be a slightly thick peudo-yogurt that our forebears knew as clabber. And while the previous generations consumed clabber in much the same way Eurasian peoples consume yogurt (as a drink, with fruit, with honey or sugar sprinkled on top), it isn’t really the same thing.
Thus the American yogurt industry relies on cultures grown from Eurasian stock. Historically they’ve only used one or two: Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus which have been judged by Western consumers as offering the most appealing combination of flavor and texture. Yogurt makers still rely heavily on these bugs, though have steadily been introducing more variety into the mix as a result of the probiotics craze (which I’ll blog more about later).
The truth is that the world abounds with interesting bugs that make yogurts of all kinds. The Japanese, for example, treasure something called Caspian Sea Yogurt, which is derived from a culture called Matsoni, a combination of Lactococcus lactis subsp. cremoris and Acetobacter orientalis. This tag team combo produces a yogurt that is at once milder than our yogurt and a bit runnier. Their key benefit, however, is that they grow happily at room temperature, which means the Japanese need no clever strategies to maintain a 110-degree growing environment. They just stir it into a container of milk, set it on the kitchen counter and the next morning they have yogurt. Lucky sods.
But look around. If you’re interested you can find all sorts of interesting cultures available from online sources. In no time at all you might become a lactic acid bacteria epicure.