I'm late to the Instant Pot homemade yogurt game, but have been having fun eating the results. I'm relatively careful about cleaning the pot and implements, but I assume that at some point I'll let some microbe(s) slip by, and end up with an unlicensed ecosystem.
Here's the question: if (when?) that happens, will the results be unappetizing or inedible, or could they actually be dangerous? For example, this answer states that he got food poisoning from his homemade yogurt.
And, if this is possible, and it happened, how would I know? Fuzz on the top? A mysterious green glow? The yogurt climbing out of the pot and menacing me?
Best Answer
Food safety for homemade yogurt works basically the same way as cooking: you are safe as long as you respect the needed time and temperature restrictions.
Yogurt food safety risks
The reason yogurt is safe after staying at room temperature is the same as in all fermented foods. It has a live bacterial culture of benign bacteria, and these fill all available ecological niches, or "spoil" them with products which humans can eat (lactic or acetic acid), so no pathogens can grow. The two risks are
A nice thing about yogurt is that its fermented nature means it typically spoils by molds instead of bacteria (at least when kept in the fridge), and molds are visible. So, if you have old yogurt (that was safely made) and it's not moldy, you can consider it safe.
The safe process for making yogurt
The proper temperature will vary with the culture you choose, the widespread ones are mesophilic (usually bifidobacteria, need 37-40°C, or 98-104°F) and thermophilic (usually lactobacilii, need 43-48°C, or 110-119°F). You have some leeway with temperature, obviously - else mixed cultures wouldn't be able to grow at all - but don't overdo it. If you were to incubate your yogurt at very low temperatures (say 30°C or 86°F) or very high temperatures (e.g. 55°C or 130°F), that would be unsafe.
Do inspect your yogurt when it is done fermenting. It is normal to notice some things which are not usual in storebought yogurt - it might have a skin of either fat or caseine, it might have visibly separated whey, it might have a slightly less smooth texture. But if it is very strange - very liquid, or smelly, or discolored, or has curdled into something closer to quark - then it is not safe to eat.
Hygiene when making yogurt
There is no need to go to extremes, such as sterilizing your equipment. You can still do it if you prefer, but yogurt is still good without it. If you use the same hygiene standard as you do for other cooking and eating utensils, that's sufficient for typical yogurt-making and yogurt-eating habits.
Stronger hygiene can help you in three ways:
Instant pot yogurt
I must admit that I have not compared the Instant pot yogurt process specifications against industrial standards, I just trust the manufacturers to have chosen a safe process. The yogurt it makes turns out comparable to making it in a sous vide setup where I can control the temperature and time precisely. So, I think it should be a safe method. An advice that is unrelated to safety: use a separate gasket, else your yogurt will taste like stew.