I'm a thick, slightly tangy yogurt lover. Like the kind I met in Greece, and is (for me) best replicated by the Fage brand. They are one of the few companies that actually strains their yogurt of enough of the excess whey to give it the right consistency.
Plenty of other people like theirs softer, more liquid or tangier. These are also completely in your reach even without adding gelatin, seaweed extracts, starch, or other odd bits added to the grocery store stuff that keeps it dependable and more shelf stable as it travels about.
The tanginess has to do with the length of fermentation. The longer the little milk digesting bacteria are left to do their work the more acid they produce.
Lactose, the main sugar in milk is digested and turned into lactic acid. This is why "lactose intolerant" individuals can eat yogurt. The lactose is eaten up, gone! Turned into lactic acid.
This is also why coconut milk yogurt works - there are sugars and proteins in there. The bacteria eat the sugar, and produce acid. These acids will then coagulate (turn solid) the dissolved proteins. But there are fewer proteins in coconut milk, so you get a thinner yogurt.
Soy milk can be made into yogurt only if there is some sugar added to it. The bacteria need something to eat and and turn to acid if the soy proteins are going to coagulate. (Most soy milk you buy at the store has some sort of sugar, so it is all set to go.)
Thick or Thin?
So what mediates the thickness? How hot you get your milk. The warmer the milk gets, the more the protein strands unravel, so they can recombine tighter, and in larger groups resulting in a thicker yogurt when hit with the lactic acid. If you heat up your milk to a lower temperature, the resulting yogurt will be looser.
This is all down to fat content. If you have non-fat milk, there will be no fat. The yogurt will be good, but it won't have the creamy richness of the fat. It's not a problem, just understand there is no way to simulate the particular mouth feel of fat.
Straining the yogurt to concentrate the solids will give it a richer texture, but it is still not the same as the creaminess you'd get with whole milk.
So what milks work?
For dairy milk - all of them. The stuff in the cartons, raw milk, box milk, powdered milk. I've seen claims that ultra-pasturized or UHT milks won't work. Not so. Milk turns to yogurt because you introduce particular bacteria into a liquid full of nutrients and relatively empty of other bacteria.
The bacteria are individual cells on the hunt for sugar, and when they find it, they eat it. Well fed, warm bacteria multiply, sending out more copies of themselves to find and digest the rest of the sugar.
Regular milk, the stuff we think of when we think of milk, has a pretty low concentration of bacteria. Since we keep it cold, what bacteria that is still in there has little chance to grow and ferment the milk. But as we all know, given long enough this milk will go bad.
Raw milk has more bacteria, but it is largely person friendly since its source is an animal that lives closely with humans. What's good for the cow gut is good for ours as well.
Powdered milk in its powdered form is free from any active bacteria since there is no water for the bacteria to live in. Once you rehydrate it (add water), it is just as open a canvas for the bacteria to move in. So populate it with your yogurt culture, and you'll get what you want. The down side? It'll still taste like powdered milk.
Ultra-pasturized and UHT (Ultra High Temperature) dairy products are super squeaky clean, (neither is sterile - that's a whole different ball game), but are so barren of bacteria they will keep extra long before going sour. And if that's what you have to work with they will do just fine, providing the materials your yogurt culture needs to live and grow.
'Nuff Biology. How Do I Make Yogurt?
Get your milk. 2-4 C is a nice amount to start with.
Not too much yogurt results, but enough to make it worth all the fiddling about.
Choose your fermentation container of choice, it needs to come with a lid.
Heavy glass jars are nice since they are reusable and easy to get super squeaky clean. I like 1 C canning jars (but only fill them about 3/4 full or a little more) so I end up with individual servings. And the canning lid rests on top nicely. No need for the screw on part.
There are special yogurt jars, but - ehh?
Glazed pottery works fine too, but you need to find a lid. In China they rubber-banded wax paper over the top - so it need not be high tech.
Get some (plain) yogurt with live active cultures.
These days most yogurts have the live cultures, but read the label just to be sure. Plain yogurt just simplifies things. (Dairy free people - get coconut or soy - still works!)
Get a cooking thermometer
I LOVE my Thermapen, a digital instant read
but a candy thermometer will serve as well.
A small bowl, a fork/whisk and a ladle
These are for mixing warm milk with the yogurt and moving hot milk about with the least injury to people.
Heat the milk to: Stir over medium to medium-high heat. Watch the temp with the thermometer.
120F - 160F super loose. In fact if you want "yogurt" like you are used to you'll need to add some powdered milk, gelatin or tapioca starch.
165F - 175F for loose yogurt. This can be drinkable after it is stirred.
175F - 180F for firmer yogurt
180F - 185F the thickest yogurt, but not yet grainy (185 is my sweet spot)
190F - boiling (212F) - starts to get a grainy texture. You are entering fresh cheese territory here. It will make a quick and dirty firm yogurt, but the texture won't be smooth. (How do I know? I tried. Not my fave, but I will be straining it to make yogurt cheese. No reason to waste those tasty coagulated proteins).
Let it cool: Either set it over an ice bath, or do other stuff in the kitchen and check on it until it hits
110F - 100F If it gets below 90F, you'll need to go through the heating part all over again. I got super paranoid my first time, worried it wasn't exactly 112F. Yeah, not such a big deal. Just keep it over 90F.
Ladle some of the warm milk into the small bowl. Use the fork/whisk to stir the still warm milk with 1Tbs plain yogurt for each cup you are making (more or less). Pour this back into the big batch of milk.
Ladle this into your fermenting jars.
Sous vide style - Pop your jars into a warm water bath somewhere between 100 - 115 (108 is the nice middle where I like to hang out). Cover the jars so condensation doesn't drip in. Let it go for 4-8 hours. (Depending on temperature, culture and how tangy you like it, 3-12 hours is a realistic range.)
Higher temps mean faster fermentation - thus faster coagulation and more whey, and sometimes a grainier texture.
Lower temps mean slower fermentation - so the curd forms more slowly, and typically incorporates more whey, and a generally creamier texture.
Cooler & a bowl of boiling water -
Line a cooler with a towel/towels. Place a large (8-12 C) bowl in one side, and the yogurt jars in the other. Use the towel to wrap and prop everybody up sturdily. Fill the bowl about 2/3 with boiling water, close the lid and let it sit about 6 hours.
Blanket and a heating pad -
This was the first way I made yogurt, and I didn't love the result. But it was definitely yogurt. It was a high temperature ferment of a mix that had powdered milk and honey added.
This works best if you have all your milk in a cylindrical container. Wrap a heating pad around the container, then insulate it in blankets. Set your heating pad to medium to start, and keep an eye on the temp. Adjust to low or high to keep the temperature at the range you want for 4-8 hours.
(For me - if I'm going with a hack, I want a low maintenance one. This one wasn't.)
In all cases - take out your jars. Does the yogurt look solid-ish? If so, pop them in the fridge, let them cool down the rest of the way.
Ta-Da! you have yogurt.
Then add honey, fruit whatever. And use it in place of sour cream. It has the same tang and it won't break apart when heated. I tried adding honey before I fermented. Not worth it. Just top your yogurt with what you want when you want to eat it. Again, it makes the whole thing simpler.
So many options!!!!!
The thing that struck me are the ridiculous range of options out there when making yogurt - how high or low to heat your milk, fermentation temperature, additions (powdered milk, honey, gelatin, starch...). But what it comes down to, yogurt is the kind of thing that happens even when you aren't trying. So the recipe is very forgiving, and all that really matters is what you prefer.
And if you made yogurt, but want it thicker, wrap it in a tea-towel or plop it in a coffee filter. Put in in a colander over a bowl for a few hours. Ta-da thicker yogurt. Or yogurt cheese. depending on how long you left it.
Like I said... so many options.
If you are not a fan of the thermometer, and have a crock pot, check out this recipe:
and then the add-on
Coconut Milk Crockpot Yogurt (will most likely work for all sorts of other non-dairy milks)