If yeast strains had feelings, which are really easy to project onto them once you start giving them names, I suspect my 15-month-old sourdough starter "Ezekiel" would be seriously cheesed about losing out on the first "culture this" series to yogurt. But turning milk into yogurt is (very marginally) easier than turning flour and water into a starter, and life is busy in the fall when you work in education and watch an absurd amount of college football every weekend. Lame excuses, I know.
Lots of people will claim that home-cultured things taste better or are healthier for you, but those are either entirely subjective or up for serious debate. The main reasons I like culturing things are
- It’s cheaper. Milk is cheaper than yogurt, so even though you have to start with a little bit of yogurt the first time, even your first batch will cost less than it would to buy the same amount of yogurt someone else cultured. And it’s not like that’s a complicated or labor-intensive process. As Harold McGee noted in his recent NYTimes article on yogurt, the bacteria are doing all the work here. Why pay someone else premium for something that takes no effort or skill to do yourself?
- It gives you more control over the process, which is part of why people often end up thinking it tastes better. You get to decide how tart, how thick, how rich, and how voluminous you want your yogurt to be. You can start with soy milk if you prefer soy yogurt or skim milk if you want it to be fat-free. You can strain it if you want something closer to Greek-style yogurt at a tiny fraction of the cost. You are the master of your yogurt kingdom.
- It’s like having a science experiment/pet in your kitchen. With both yeast and yogurt cultures, you’re basically cyclically growing more by feeding them and putting them in a hospitable environment. They multiply like crazy, and when you have enough of them to suit your purposes, you crush their little yeasty or bacterial dreams of total world domination by putting them back in a less hospitable environment. There’s a nurturing appeal, too, which probably seems to conflict with the idea of thwarting their imagined imperial ambitions, but it’s true: I like the sense of ritual and continuity. For yogurt, I like saving the last few tablespoons of every batch for the next one, swaddling the container in towels to keep it warm, and knowing when I eat it that it’s something I fed and grew
Sold? If so, I welcome you to "culture this" part 1:
How to make some milk and a little bit of yogurt into a lot of yogurt
I know it doesn’t sound super impressive when I put it that way, but it’s not super impressive once you’ve done it. If you’re looking to impress, you can call it "Homemade Yogurt" and not really be lying, but this not like a "wild" sourdough starter* where you’re cultivating yeasts in the flour or in the air that will thrive in precisely the conditions you set up in your personal kitchen. If that kind of sourdough is growing from seed, or raising volunteer plants, yogurt is planting a seedling you picked up at the local nursery. Basically every recipe I’ve seen for "homemade yogurt" involves a starter culture. This is also probably why I haven’t named mine—I sort of feel like its proper name is "Mountain High Yogurt," because that’s the brand I started with.
The whole process goes like this: you heat some milk until it steams, you let it cool back down until it’s warm but you can put your finger in it without too much discomfort, you stir in a few tablespoons of yogurt, and then you let it sit for 4-24 hours.
Step 1: Heat approximately the volume of milk you wish to culture to 180F
I use a ceramic crock I picked up for $2 at a re-use store, and generally just measure out the amount of milk I want by filling the crock up most of the way and then pouring that into a pan. Not super scientific, I know. If you want to make a specific amount of yogurt, measure out that much milk less 1 oz per cup for the yogurt you’ll stir in as a starter. If you’re planning on straining it, use approximately twice as much milk as you want to end up with in yogurt.
Don’t skip this step, or you’ll kill all the bacteria. I did that the second time I tried this because I thought I remembered how to do it and didn’t need to look it up again and ended up throwing it out, although I probably could have just added more yogurt, but I didn’t have any at the time and this is all sort of contrary to the whole economical argument but the point is, don’t forget to let the milk cool back down. Just like yeast, temperatures over 120F will kill it. Apparently the reason for heating it to 180F rather than just taking it up to 120F in the first place is that the higher heat changes the whey proteins and, McGee says, "helps create a finer, denser consistency."
Step 3: Whisk in approximately 1 oz. yogurt for every cup of milk you’re using
You can use any kind of yogurt with active cultures, and like McGee, I’ve found that the cheaper the yogurt I start with, the better my own stuff turns out. The more expensive unsweetened, organic, or Greek-style yogurts often only have one or two kinds of bacteria in them whereas the cheap stuff generally has a lot more and they’re apparently super active. Sure, those brands also tend to have sweeteners and additives, but all of that will get diluted so much in your end product that they won’t affect the taste much, if at all. Certainly not by batch #2.
McGee recommends 2 T. per quart, but I tend to use a little bit more. The amount of starter culture and length of time you let it sit are what will determine the tartness and consistency, so you can play around with both to figure out your own "perfect" yogurt.
Step 4: Put in an insulated airtight container and seal
This is where the crock with the airtight seal comes in handy, but I imagine plastic wrap and a rubber band would do just as well. Whatever your vessel, you’ll want to wrap it in a few towels. I secure mine with mega rubber bands like so:
Step 5: Taste every 4-hrs or so to see how it’s coming along
Try not to stir it, as you want to keep the milk still until it sets, but you can take just a little off the top to see how tart and creamy it is. McGee says four hours will do it, but I’ve had better luck letting it sit 12 or more hours, usually overnight. Earlier than that and I’ve gotten really mild, milky results.
What’s happening as it sits is that lactic acid produced by the bacteria causes the protein and fat in the milk to form a continuous network, which the water gets suspended in (well, except for the part that leaks out or pools on the top, which is whey). Those networks are what make yogurt thick and creamy.
Skim and soy milks will never set up as thick as whole milk, which is what I generally use. Commercial manufacturers often add gelatin or starch, which I imagine you could do at home. Using starch, I would probably start by making a paste of 1-2 T. corn starch or arrowroot powder and an equal amount of milk, and then I’d whisk that into the rest of the milk before heating. Using gelatin, I’d just sprinkle a package or two over the cold milk before heating and let it sit or "bloom" for 5-10 min and then heat as usual, stirring constantly and making sure the gelatin dissolves. I can’t say for sure that would turn out great, but if you’re a soy or non-fat yogurt eater and you want to try making your own at home for cheaper, it might be worth a try.
Step 6: Refrigerate and enjoy
The yogurt will continue to set once in cold storage and the lactic acid production will slow to a halt. Kept cold, it should last for weeks—the acid helps preserve it much longer than fresh milk.
I love it for breakfast sweetened with Grade B maple syrup (which is cheaper, more flavorful, and more nutrient-dense than Grade A) and topped with fruit and granola. I also love it salted and mixed with vegetables and/or herbs as a sauce with fish. And strained, sweetened, and frozen it makes a great dessert.
Optional Step 7: Strain
If you want a thicker, Greek-style yogurt, pour it into a cheesecloth-lined colander or a fine mesh strainer and suspend over a bowl for several hours. The yellowish liquid that drains out is whey, which contains protein and a number of vitamins and minerals. Some athletes drink whey, often sweetened or salted, as a workout-recovery drink (whey powder is also part of many supplements). If you’re not into drinking it straight, you can also use it as some or all of the liquid in most baking recipes. Processed foods sometimes contain whey, so I’m sure food product developers could tell you what difference it makes but so far, I haven’t been able to tell.
*Scare quotes for "wild" because I’ve been convinced by Aaron Bobrow-Strain that even sourdough starters cultivated without the use of packaged yeast or a pre-made starter aren’t really "wild." Much like corn and dogs and modern chickens, yeast and human civilization co-evolved, so even seemingly "wild" strains of s. cerevisiae yeast are the product of agriculture and human-yeast interaction. That said, there ought to be a way of distinguishing between starters that rely on booster yeast or heirloom yeasts and the ones that you grow in your own kitchen to fit your personal rhythms of baking. Apparently Bobrow-Strain has been working on something for publication about baking and yeast ecology with Melanie DuPuis so I’ll try to keep an eye out and post the reference for anyone interested in that sort of thing.