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My understanding is that yoghurt is is the biproduct of a yoghurt culture, a bacteria, eating lactose and excreting the yoghurt.

My question is - why does it need to be lactose that the yoghurt culture is eating?

For yeast to produce alcohol, for example, the yeast can eat any sugar, and it's up to the brewer to decide whether that's sucrose, corn, barley, grapes etc to affect the taste.

Why is that that yoghurt cultures need lactose specifically?

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    Your understanding is woefully incomplete - yeast actually don't eat lactose, for instance, which is why it's used in "milk stout." As for how yogurt is formed, I'll let someone else tilt at that windmill, but it's hardly a matter of "excreting yogurt." – Ecnerwal Oct 18 '15 at 23:47
  • I'm not sure this question should stay open. What would be a culinary answer to it? In my eyes, any explanation beyond "yogurt cultures eat lactose because that's what yogurt cultures eat" would have to involve the biochemistry of yogurt cultures. – rumtscho Oct 19 '15 at 10:08
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    @rumtscho- The question betrays a fundamental misconception that the only ingredient required for yogurt is sugar. So yes, the question may not be generally useful because it has a flawed premise but it is still a valuable question for dwjohnston (or anyone with a similar misconception). – Sobachatina Oct 19 '15 at 18:59
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Lactobacillus is the genus of the bacteria responsible for making yogurt.

These bacteria consume sugars and excrete lactic acid. The acid denatures the proteins in the milk, causing them to coagulate into a delicious gel.

Lactobacilli can consume sugars other than just lactose.

https://en.m.wikipedia.org/wiki/Lactobacillus

The reason they eat lactose when making yogurt is because that's what they have. There is more than enough lactose in milk to make yogurt. There's no reason to add other sugars.

Lactobacilli are also responsible for the fermentation of pickles. In that case, even though they still produce lactic acid, they are consuming the sugars available in the vegetables, not lactose.

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    Ok - so is the reason you need dairy to produce yoghurt, more because of the protein in the dairy? - ie. you could grow the lactobacillus without dairy/lactose - but then all you'd have is lactic acid - you need the protein + lactic acid to get yoghurt? – dwjohnston Apr 6 '16 at 2:42
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    That is correct. – Sobachatina Apr 6 '16 at 3:17
  • What would happen if you took sugar, lactobacillus and some other form of protein? – dwjohnston Apr 6 '16 at 4:05
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    That is a very broad question. The broad answer is that you would get whatever that protein forms when exposed to lactic acid. How different proteins would behave is beyond my knowledge. I've experimented with soy and cows milks. – Sobachatina Apr 10 '16 at 16:05
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    One more reason is that relatively few bacteria can consume lactose, so you're unlikely to end up with spoiled product that got dominated by a completely different strain of bacteria. – SF. Apr 25 at 10:38
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If you are lactose intolerant or you avoid animal proteins, a thick custard style yogurt culture can be made with yellow pea protein non-dairy "milk". I am not sure if you have access to non-diary milk products made with pea protein, but they are becoming more popular in the U.S.A. and are much higher in protein than other non-dairy milks. A small amount of sugar in the milk is helpful to kick-start the cultures, and the standard (non unsweetened) versions of these milks contain what you need. Just as it is with dairy milk, it is important to heat the non-dairy milk to about 180 F (82 C) and let it cool to 110 F (43 C) before introducing the cultures. The heating helps with the denaturing of the proteins once the cultures start their process, and you will end up with a thicker, more creamy yogurt.

  • This is interesting. I'll have to read into it more and try it out. When I experimented making tofu acid was not an effective coagulant. I wonder how the yellow pea is different. – Sobachatina Jul 18 '17 at 21:41

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