Pre-Cheese Processing question...

[Eucherplayer]

I have a friend that is giving me the "extra" cow's milk (left over from feeding his calves).  Up until about a week ago, everything was fine, cheeses were coming out great.  I pasteurize ALL the milk at 145 degrees for 30 minutes (standardized process here), and place it into "skimmers" to save the cream for butter and to re-add to cheese recipes where needed.  Over the last week, I have been finding that the milk has started to coagulate after pasteurization in the skimmer.  The milk smells normal (sweet), and tastes good, but it will not form a proper curd for making cheese, instead, it looks like vinegar has been added when it gets to temperature (without any additives)...  Have any of you experienced this before?  Any ideas?

[Sailor Con Queso]

I suspect that bacteria have acidified the milk. Check the pH of your milk before and after pasteurization. If natural bacteria are allowed to multiply, they will start to produce acid and the pH can be too low for making cheese.

[Eucherplayer]

Thank you Sailor for the fast response, and that makes sense, as I am picking up the milk in the evenings only at this point (the other thing that changed in the last week or two).  It is placed directly into the 'fridge - but who knows how long the bacteria have to multiply in the mean time.  Now, I have to figure out if there is a solution...  This Forum ROCKS (BTW)!    

[steffb503]

Placing warm milk directly in the fridge is most likely the problem. Any bacteria present just love how long it takes to cool down in the fridge. Big no-no! It should be cooled down to below 45 within 2 hours before going in the fridge.