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Can you let your mother cultures incubate too long?

I did a thermophilic mother culture last night and ended up falling asleep. It was in my fish tank heater, cooler set up which I use for yogurt making. It was 97.f when I checked it this morning and the culture seemed rather firm though I've not opened it up yet.

I also have a pH meter. Will measuring pH tell me things about if I've gone too long?

Thanks.

I would think there is some upper limit, but I don't know what it is. On the one hand, my reading suggests that the lactic bacteria die out relatively quickly in the aging process, but they leave behind all sorts of enzymes that continue to age the cheese. Of course, some of that die out may be due to the drying out of the curds and the salt. On the other hand, the yogurt you buy in the store with "live cultures" is, in essence, milk that has been allowed to curd due to acid production of a thermophilic bacteria. Presumably the fact that it is refrigerated is part of why the bacteria are still alive for an extended time.

So, here's my helpful answer: it depends.

The lower the pH goes the less viable it will be. All bacteria will basically die off around 4.6 but a lot of them will be suffering long before that

I've held starter cultures in my cooler (heated rather than cooling) for upwards of about 20 hours.  I wouldn't worry.  I've also held yogurt in my fridge for more than a year and successfully made more yogurt from it (with no noticeable performance problems).  The only thing I recommend (which is what I do) is that if you are freezing a mother culture, restart it from the frozen one and use the resultant fresh culture.  Possibly I'm paranoid, but I always think it's best to work from the healthiest culture possible.

Thanks for the help. It seems ok. I used it to make several gallons of yogurt and they seem fine.

I'm still confused on why mother cultures "fade". It doesn't make any sense to me. Seems like a numbers game, but I guess I just have more to learn. I know some things "senescence", but I've never actually been able to notice it. I've heard about it more with mycology but I guess it must be the same theory with bacteriological cultures.

Quote from: Montana Kosher on March 21, 2019, 03:06:16 AM
Thanks for the help. It seems ok. I used it to make several gallons of yogurt and they seem fine.

I'm still confused on why mother cultures "fade". It doesn't make any sense to me. Seems like a numbers game, but I guess I just have more to learn. I know some things "senescence", but I've never actually been able to notice it. I've heard about it more with mycology but I guess it must be the same theory with bacteriological cultures.

Don't forget the phage problem. Bacteria get viruses and if your culture gets a viral infection it will struggle. This why the pros rotate their cultures - different strains get different viruses so every time they change cultures, the viruses have to start all over again. Repeatedly reculturing under home kitchen conditions practially guarantees the culture will become infected.