The odds are very good that it is a milk problem. Check the milk or curd below the surface. Bring a spoonful up from the bottom and if it is different, you have a problem milk. Try your recipe again with a good local cow's milk. Whenever possible, look for a local brand. This is because long, cold storage and transportation is problematic for milk. The closer the milk is to the source (cows, goats, etc.) the better for cheese making. Another factor is the heat at which the milk has been pasteurized. If the milk clearly states that it is ultra-pasteurized (UP), do not purchase it. It has basically been stripped of friendly bacteria. More importantly, the alteration of the proteins is so severe that the milk will not form a proper curd. Unfortunately, even if your milk is not labeled UP, it may have been heated to just short of ultra-pasteurization. When milk has been pasteurized at a high temperature (anything over 172F), it is problematic for cheese making. The only way to know how high a processor has heated their milk is to call them. We encourage you to do this because we believe it will let the large processing plants know where we stand.
Oct 25, 2019