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I’m on a SIBO diet which allows only yogurt that’s been fermented for 24 hours or more. I read plenty of articles about how to make this (and I’ve made standard 8-10 hour yogurt before). They all say it should smell sweet and fresh. Well mine turned out with quite a strong somewhat cheesy smell and a lot of whey separation.

I used lactose-free milk and powdered cultures (and the cultures were quite old), so I thought one of these two things must have spoiled it. I threw it out and got new cultures as well as standard 3.3% A2 milk. I left it only for 14 hours this time and… same.

Is this how it’s meant to be, or otherwise is it safe to eat? It doesn’t smell rotten and there’s no mold, but quite sour.

I sterilized all pots and utensils in boiling water, I used a thermometer for precise temperature reading and I used a yogurt pot that kept it at 42°C the whole time, so I know that’s not the problem.

Perhaps the amount of bacteria was too much for this long period of time and it ran out of lactose to feed on? I used the appropriate amount that the packaging stated for 8 hour fermentation period.

Here’s a photo of the second attempt at 14 hours (the bubbles on the surface are from the whey liquid on top, and it probably looks more yellowish than it actually is due to the lighting):

enter image description here

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  • Usually when making yoghurt you heat the milk to around 85C, essentially pasteurizing it, before letting it cool to 46C before adding the culture. If you don't do this, then the yoghurt may go off since there may be undesirable bacteria in the milk. Sterilizing the pots alone won't prevent this. TBH, I wouldn't eat anything that doesn't smell right. That's your nose giving you a warning!
    – Billy Kerr
    Mar 27, 2022 at 12:09
  • Hi, I did do this of course. Sorry I should have mentioned it in my post. I heated it to 89 deg and kept it there for 10 mins to help thicken the yogurt. Mar 27, 2022 at 16:57

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Yes, it is safe. This is just the normal smell of yogurt, or rather, its cultures. We are accustomed to consuming yogurt which has been carefully fermented to get the least possible culture smell, but this is a modern invention. Decades ago, yogurt was supposed to be smelly, and some people still prefer it that way.

This is not to say that yogurt cannot get undesirable (I don't know if pathogenic) cultures when overfermented, but this usually happens if you keep it for days outside of the fridge. The bacteria will make a yellowish film, a bit hard to distinguish against the yogurt surface (especially if you have a fat cover on the yogurt), with its own distinctive smell. But I don't think 24 hours in the fridge is enough for that to happen.

You could set a small bowl of yogurt outside of the fridge and observe how it goes bad, just to have seen it once and be able to judge what actual spoiled yogurt looks like. Then you'll know when it is time to toss an actual batch, should it go bad.

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  • Hi, I kept it fermenting at 42°C for 24 hours. Not in the fridge for 24 hours. But thanks for clarifying about the traditional smell. Mar 27, 2022 at 16:58
  • ah, sorry if I wasn't clear. My point was that you have to keep it in the fridge after fermenting, the fermentation itself always happens in the range you mention.
    – rumtscho
    Mar 27, 2022 at 17:48
  • Ah yes, I did transfer it to the fridge immediately afterwards :) Mar 27, 2022 at 20:50

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