Super Food Nerds: How to Make Your Own Yogurt
Superfoodnerd Milder here, reporting this month on Project D.I.Y. Yogurt. Let me start by saying that I came to this with some trepidation, scarred by a personal history of sour milk and thin, lumpy yogurts of my own making. I had read the articles ("better than anything you can buy!"), seen the blog posts ("idiot proof!"), followed the recipes -- and the recipes had failed me. I knew I was in for a fight on this one.
And quite a fight it was. My first few attempts were utter travesties of spilled, wasted and spoiled milk. I killed my starter culture; I ruined my curd; I scalded my hand; I threw out my back. I would have cried, were I anything less than a steely-eyed superfoodnerd. No, I picked myself up, straightened my pocket protector and set to work. It took considerable research and tinkering, but ultimately I did manage to break through to yogurt — really, really good, smile-across-your-face yogurt. For all its difficulties, this was a project with a big payoff.
That said, I cannot promise you perfect yogurt. Yogurt promises nothing — no more than a tomato seed promises a beautiful tomato. You might, under the right conditions, get your tomato -- but you might not. You don’t call the shots. And that is the first thing you need to know about yogurt.
Yes, the thing to know about making yogurt is: you don't make yogurt; you grow it. Lactobacillus bulgaricus and Streptococcus thermophiles — heat-loving (thermophilic) bacteria with the unique ability to feed on lactose (milk sugar) and convert it to lactic acid — they make the yogurt. You grow the bacteria; you feed it; you tend it. You plant your garden and, if you were reasonably careful about setting the right conditions, you reap a harvest of yogurt. It all comes down to the lactic acid bacteria. (In a very real sense, yogurt-making is not culinary. It is cultural — as in agricultural or horticultural.)
Knowing this, in and of itself, doesn't get you any closer to good yogurt. But it may put you in the right frame of mind, and that is important. My first, failed batches were a direct result of my mental unreadiness: I rushed; I futzed; I failed to observe.
Oh, and here is one more thing to know: yogurt makes yogurt. Our friends Lactobacillus bulgaricus and Streptococcus thermophilus teem inside every container of "live" or "active" culture yogurt. A mere tablespoon or less, containing millions of these bacteria, is all you need to make your batch.
Okay, so the fundamentals of yogurt making are really pretty simple. They break down into four steps:
1) Heating. Milk should be heated to a minimum of 180 degrees F to kill off any native bacteria and to denature the whey proteins, which makes for a thicker yogurt. 180 is just a minimum, though, and you should feel free to play around with this. Traditionally, milk was boiled for an extended period, which concentrates proteins through evaporation and makes for a much thicker yogurt. (Commercial producers still do something similar by holding milk at 185 to 195 for as much as 30 minutes during heating.) Essentially, the more concentrated the milk, the thicker the yogurt.
2) Cooling and Inoculating. The milk is allowed to cool to about 115 degrees, at which point the bacterial starter culture (a small amount of yogurt) is stirred in. The surest way to ruin a batch of yogurt — as I know from hard-knocks experience — is to add the starter when the milk is too hot. Kill, or in any way impair your bacteria, and you'll get nothing but warm milk.
3) Incubation. This is where the magic happens. The inoculated milk is sealed away in a container and kept warm for a good long time. Warmth and the presence of an abundant energy source in the form of lactose inspire a veritable summer-of-love among the lactic acid bacteria: within hours they've multiplied a hundredfold. These bacteria, in turn, ferment the milk by digesting its lactose and converting it to tangy lactic acid. In its turn, this lactic acid coagulates the milk by causing the milk's protein and fat globules to gather into a continuous solid network, capable of holding 25 times its weight in water. This is yogurt.
The precise times and temperatures of incubation are subject to wide variation, but most recipes call for incubating between 110 and 115 degrees for anywhere from 3 to 8 hours. The higher the temperature, the more rapid the production of lactic acid and the faster the coagulation — though, there are virtues to taking it slower and lower.
4) Chilling and straining (optional). The final step. The fermented yogurt is transferred to a refrigerator to slow fermentation to a crawl and further firm up the yogurt's structure. Greek yogurt is made by straining away much of the yogurt's whey, and this is perfectly easy to do at home with a fine mesh strainer. But the simple act of pouring off a little of the free-floating whey, either before or after refrigeration, is enough to thicken a yogurt nicely.
Discovery or: The Battle Turns
As mentioned earlier, my initial yogurts were abject failures -- humiliations. But the battle did swing in my direction. Here's how:
The first breakthrough came courtesy Rick Martinez, the freshest new face in Food Network Kitchens, who suggested I try using some half-and-half in my yogurt. I did, substituting half-and-half for about a quarter of the total milk. It made a huge difference — not just to the texture, which became pudding-like, but to the flavor, which deepened profoundly. After making several yogurts with varying fat levels, I have no doubt that truly great yogurt is not a diet product. Fat makes a huge difference.
The second breakthrough came in the incubation phase. Most recipes prescribe incubating for 4 to 6 hours at 110 and 115 degrees — a devilishly hard temperature to maintain without a yogurt maker. I did try it and yes, you'll get yogurt that way. But you're only scratching the surface. At these higher temperatures, you do get faster coagulation. But that short span of time is not enough for serious flavor development. And too much time at these elevated temperatures can cause the yogurt to curdle and sour. The best yogurt, the yogurt with the roundest, most complex flavor, only develops over much longer fermentation at much lower temperatures — as much as 24 hours, with much of that time spent between 86 and 102 degrees. Of course, this produces its own set of challenges.
The greatest obstacle to making yogurt at home is in finding a way to maintain this temperature range over a long period of time. I've had some success incubating in my gas oven with the pilot light on, and I've seen reputable authors recommend incubating in a coffee thermos. But far and away the most successful solution I've found has been a simple picnic cooler.
The same thermal stability that allows coolers to keep cold foods cold enables them to keep hot foods hot — especially if you preheat them well. But coolers aren't perfect, and that turns out to be their greatest virtue. They lose heat, only very slowly. You can start incubation at the high end of the fermentation range (110 to 115) — good for setting a firm curd — and then allow the temperature to fall for over the course 15 or more hours. The cooler I used gradually dropped from 110 to 102 degrees over 15 hours. After another 10 hours, it had fallen to 93 degrees. The result was very full-flavored — nutty and buttery, with a tangy, green apple acidity and a thick, creamy texture that was more akin to creme fraiche or mascarpone than to your average yogurt.
This is the yogurt I was after all along. This is the yogurt that, with the accompanying recipe, I hope you will be able to taste for yourself. It is not an easy recipe (attention to the finer details is paramount), and neither I nor yogurt can offer you any promises. But, then, you don't make yogurt because it's easy. You make it because it is a minor miracle — a magical transformation of liquid into solid. And the only way to witness that is to make it yourself.
1) Be Still. Yogurt must be left completely undisturbed during the first 4 or 5 hours of incubation, to allow its fragile web of coagulated protein and fat to form properly. The merest jostle may be enough to alter the final set. Don't even look at it funny.
2) Taste and Test. Once yogurt has set up—about 5 hours of fermentation—you no longer need to baby it. Remove the yogurt from its incubator and taste it. Now, taste the yogurt you used as a starter. That's a good reference point for determining whether your yogurt could use more time to develop additional flavor and acidity.
3) Hit Refresh. Reserve a tablespoon of yogurt for your next batch, but know that this will only work for a couple generations. Modern lab bred bacterial cultures do not survive for long outside of the laboratory. Traditional yogurt cultures were drawn from a much more heterogeneous microbial community. Today's yogurt is produced from very pure bacterial strains.