The math behind the quantity of yogurt starter and the volume of yogurt it makes

Every now and then I get asked the same question so I decided to write a quick explanation about it.

Sometime clients will email me saying “Hey, there is something off here — if the 1L pack contains 1 gram of starter, how come I didn’t get a pack of 50 grams with my 50L pack? Are you trying to scam me?

And while this is a novice questions, and everyone who makes yogurt regularly knows why this is so, for the people who are just starting it might indeed seem like something is off.

So let me quickly explain what’s going on.

If you make a simple algebraic calculations, then you’ll quickly come to the conclusion that if 1 gram makes 1 liter of yogurt, then 10 grams should make 10 liters of yogurt, right?

In fact, you can’t be more wrong 🙂

The confusion comes from the assumption that the quantity of starter required to make yogurt is a linear function to the quantity of yogurt that it makes. While actually it is much closer to an exponential function.

The yogurt starter quantity to volume of yogurt it makes is not a linear but an exponential function

It takes a gram of starter to make a liter of yogurt, it takes about 10 grams of starter to make 50 liters of yogurt, and it takes a mere 400 grams of starter to make 10 metric tons of yogurt.

That is a lot of yogurt!

Now get some starter!