For anyone wondering why this works, and why the link's technique is so complicated, remember that humans have been making yogurt for thousands of years. So you don't need anything fancy to make yogurt.

Even a fridge is not needed. Put the milk+yogurt mix container in a clay pot placed in a tray of water, and it will turn into yogurt.

Anything fancier on top is just to reduce the amount of work needed or have longer fridge life.

Right, many recipes in this thread are fancy. No need to get in such a ferment about it (pun intended). May be needed for colder northern climes, but I have my doubts. (E.g. people were making yogurt in similarly cold Central Asia for centuries, with out such data structures and algorithms, er, containers and instructions.) In India, mothers and housewives (and nowadays househusbands) routinely make curd (Indian English name for yogurt, dahi in Hindi), just by warming (c)old milk (or cooling just-boiled new milk down some), bunging some old curd in (e.g. 1 to 2 tbsp per liter milk) putting it in a slightly cooler or warmer part of the house, depending on the season), and forgetting about it for 8 to 24 hours. That's it. Dead simple. If not come out well, tweak a parameter or two, retry. But mostly it goes smoothly (pun not intended but retained).

The old, traditional yogurts were made by using soil (yes, literally earth). The soil had the bacteria required :)

This sounds brilliant - I'll give it a go tonight!

On a different note, I grew up in Eastern Europe before it became capitalist and used to spend my summer holidays in the countryside. Needless to say,almost nothing was pre-packaged or ready made and everything was made from scratch, including yogurt. I can't really remember exactly how my grandmother made it, but I think she followed a similar process. I remember very fondly how it tasted, cool and slightly tart on a hot summer day; obviously these memories make me want to try it even more!

Somebody once told me that smokers smoke hoping that each cigarette will taste like the first. I can't really comment on that, but personally, every time I eat yogurt I hope it will taste like it did in childhood.

This is how my mother does it too.

You just need good bacteria to start with, called the "culture", for your next preparations you can just get a sample from your previous yogurt.

The yogurt you get from stores with preservatives and ultra long shelf time, a.k.a. all bacteria is cleaned up to prevent it going sour, wont work, find someone that has real yogurt.

That's the reason for using a probiotic yogurt. They add the relevant bacteria after they finish ruining it :)

The problem with using yogurt from the last batch is that usually there is nothing left when you finally get to making the next batch... :)

Well, we usually just keep at least one teacup of yogurt to avoid the situation where none has left as you have mentioned be able to make more :D

Yeah, well... The kids have a tendency to find and eat anything that happens to be in the fridge :D

Are you using some local milk? I use "bio" milk and I'm pretty sure (by the expiration date being at least a month into the future) it is UHT, so no need to boil the milk?

Boiling denatures some of the proteins, and gives you more of the texture you expect. From what I understand, if you don't boil it the texture will be very runny.

ELI5 - Boiling makes it easier for the bacteria to eat.

Also evaporates some of the water.

Using whole milk (also works fine with regular milk), refrigerated, so probably not UHT.

You should boil the milk anyways, you want all other bacteria/bugs dead and only the "wanted" bacteria to "spoil" the milk. Otherwise the result could be unpredictable.

Boiling the milk also helps the bacteria to work faster.

> You should boil the milk anyways, you want all other bacteria/bugs dead and only the "wanted" bacteria to "spoil" the milk.

UHT milk tends to be sterile, if it's straight from an unopened carton.

Hard to ruin recipes are the best recipes.

That's almost exactly how I do (The difference is that I use a thermometer).

I'd like to hear more about why you make your own yoghurt. Does it taste very different than store bought plain yoghurt, do you find the DIY aspect appealing, or is it mainly for cost savings?

I personally do it because I get a better consistency and taste, with lower lactose than in commercial varieties, and save a couple of bucks. It's really easy to make, I use a teaspoon of the previous yogurt batch as a starter and let it ferment 13 hours in 1L of milk, in the oven with the oven light on. Too much starter and it ferments too quickly, gets chunky and sour.

I do it to make full-fat, low-sugar yogurt, which is harder than it should be to find at the grocery store. Almost all of them besides the Fage Greek are loaded with sugar. Guess which one our store doesn't stock? (the Fage 5%)

In Spain you can find everywhere "natural yogur", not sweetened, with "4 g sugars", I guess lactose, per 100 g, so 5 g per 125 g cup. Is this low-sugar by your standards or is it possible to achieve lower contents?

Yes, I'm referring to "no sugar added" really. As you mentioned, there is some natural sugar.

Most yogurts here contain various additives for firmness, which usually means some kind of processed sugar, which I prefer to avoid. There is also the quality and the price aspect.

Also, it's fun.

You can clone any expensive yogurt for small price and control the ingredients fully.

You need yogurt to make yogurt?