Author Topic: Testing a culture  (Read 391 times)

Offline Kirkbybil

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Testing a culture
« on: March 13, 2013, 06:10:56 PM »
Hi,  I made my first batch of starter culture just over a month ago and froze it in ice cube trays.  I read that it will only last around a month so I want to know whether to just throw it away or whether I should test it and, if so, how?

I've read in several places that you test it by 'seeing if it thickens your milk' but under what conditions?  Presumably the same as when I made it originally, but that seems a lot of work just to test it. Can I just put a cube in a cup of milk and keep it warm for 24 hours and if it thickens it is still okay and I can make another batch from it or is there a correct way?

Any help really appreciated, I'm going to make more cheese at the weekend and don't want to waste it if that's not necessary.



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Offline linuxboy

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Re: Testing a culture
« Reply #1 on: March 13, 2013, 06:28:02 PM »
Quote
I read that it will only last around a month
Not accurate. The cell viability decreases, but it's not an either/or situation. You can keep using the cubes, just use a bit more over time, or reconstitute before to give them a chance to wake up and start growing.

Quote
if so, how?
1% amount at 90F meso should drop the pH to 4.8 within 6-8 hours (meaning thicken the milk to be like cultured buttermilk). If it takes longer, can gauge strength based on how much longer.
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Offline Kirkbybil

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Re: Testing a culture
« Reply #2 on: March 14, 2013, 07:10:10 AM »
Thanks, just to clarify as I'm quite new to this (but learning fast!).

If I want to test it -  I add a 1oz cube to 100oz  (1% volume as per your comment?) of skim milk at 90F and, keeping it at that temp it should thicken (to yoghurt consistency? - I don't have a ph test kit) in 6-8 hours. 

If it does that then it's good to use as per recipe.  If it takes 25% longer, for instance, then I use 25% more?

Is this correct?

Offline linuxboy

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Re: Testing a culture
« Reply #3 on: March 14, 2013, 08:15:57 AM »
Quote
If it does that then it's good to use as per recipe.  If it takes 25% longer, for instance, then I use 25% more?
Not exactly. If you do not have a pH meter, it will be very hard to tell how much more or less to use. The reason is because lactic bacteria at that temp multiply once every 25-30 minutes. So if it genuinely takes 25% more time, and you kept conditions (temp) steady, it means that it takes that many more replication cycles to get the pH down. But it doesn't necessarily take 25% more bacteria up front because of how pH works with bacteria in their lag-growth-maintenance-death lifecycle.

The biggest consideration is what is the pH when you add rennet, and what is the acidity curve for the cheese. If it is taking too long to start producing acid, then the acidity curve is thrown off.

A good rule of thumb is to add 5% for every month the culture has been in the freezer, and to reculture with a new batch and refreeze after no more than 6 months in the fridge.
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