I'm working on my 20th or so cheese. I get my milk from a local dairy (raw milk). I put it in a glass carboy and keep it outside. I've used most of the milk and it all behaved as expected and I have my rennet additions down so I'm almost always looking at a 12 min flocculation time.
I decided to use my last gallon + to make a queso fresca which I havn't made before. The milk was outside and it got down to 22 degrees. The edges froze but the milk itself didn't freeze. I"m following John's reciepe here: http://cheeseforum.org/forum/index.php/topic,1790.0.html
So I warmed the milk to 90 degrees, added a mesophillic culture and let ripen for 60 min.
On my lipase it says to add it just before the rennet...so in John's recipe he adds the lipase with the culture...I waited and added it after 60 min (after letting it rehydrate for 30 min per the package) and then added my rennet. I always use 1/4 tsp in 1/4 cup cool water for 2 gallons of milk...but I knew I only had 1.25 gallons of milk. However, I didn't want to "under rennet" so I added JUST under 1/4 tsp of rennet.
Anyways...30 min later I STILL didn't have flocculation. I'm thinking that the super cold milk could be the trouble? I've NEVER had this happen before! Normally my milk and cheese are so predictable! And I've made 3 other cheeses from the same milk and ingredients in the last 7 days.
FYI - after an hour I decided to push forward with the recipe with a super soft curd. We'll see what I get