Can someone tell me if the live cultures in yogurt increase with incubation time? I've been unable to find an answer.
What do you mean? Do you mean if bacteria multiply? Yes, up to the maximum concentration that the pH will allow, which is somewhere around 1-3 x10^9 CFU/g at a pH of 4.0-4.2 for yogurt.
Yes. I'm trying to maximize the CFUs I'm getting from my yogurt so I'm not sure how to go about this. I've read that the more sour the yogurt (the longer you incubate), the more live cultures it contains, but I don't know if it's true. I figured you guys would be the experts.
I'm a cheese making newbie (been making yogurt for about 8 months) so the rest of your post is greek yogurt to me. LOL When does yogurt reach a pH of 4, generally? I don't have a pH meter and the strips I had didn't work.
QuoteI've read that the more sour the yogurt (the longer you incubate), the more live cultures it contains, but I don't know if it's true
Its true but up to a point.
I can see the abillity to keep the Ph constant\optimal by introducing a base and keep feeding the culture with lactose (which they constantly deplete in their acidification process) and keep them growing happily.
I wont be suprised if thats how they grow the high population dried cultures in the lab.
But they use an artifical inoculum not milk since its more cost effective and sterile.
Thanks i am also searching for the information on this topic.Keep as updated
The longer you incubate yogurt, the more bacteria are produced. That also means more acid is produced. As acid is produced the bacteria will quit reproducing & die off. If you see whey on the top of your yogurt, you have probably over incubated. If you want milder, less acidic yogurt, just incubate less before you refrigerate.
Quote from: woozie on September 10, 2010, 06:59:13 PM
Yes. I'm trying to maximize the CFUs I'm getting from my yogurt so I'm not sure how to go about this.
Well, I already posted how. You culture until you hit the equilibrium point, which is 4.2 for yogurt. At this point, you have the most number of viable, living cultures. In practice, because some growth still happens as the yogurt cools, you can safely put in the fridge at 4.3 and be confident that you have reached the highest possible colony size.
If you have no pH meter, a good rule of thumb is to wait until it coagulates and add 4-6 hours after that, which should correspond to a pH of 4.4 or so.
Now if you want to engineer and manipulate, such as by adding ammonium hydroxide, to increase CFUs/g, you can also do that. But then you really do need to use pH.
Quote
I've read that the more sour the yogurt (the longer you incubate), the more live cultures it contains,
Absolutely not true. After you hit the tipping point of 4.2 or so, most types of probiotics will rapidly die off. Some start dying even earlier, around 4.5.
QuoteI'm a cheese making newbie (been making yogurt for about 8 months) so the rest of your post is greek yogurt to me. LOL When does yogurt reach a pH of 4, generally? I don't have a pH meter and the strips I had didn't work.
Depends on the amount of you start with and your milk. Generally, after 20-24 hours of incubation when using a 2% starter amount.
QuoteThanks i am also searching for the information on this topic.Keep as updated
I already posted a very concise and exact answer. Not sure what more you need. Do you want a chart?