If I remember, they are repackaging the cultures that they buy in bulk. I don't know if they are accounting for the difference in cultural activity. For an acidity issue like yours, you'd be using less culture. It's the cultures that are eating up the lactose and converting it to lactic acid. The rate of pH drop (lower pH = higher acidity) is a function of amount of culture, temperature, and even time. The bacteria are reproducing every 20 minutes, so you can see the pH can drop fairly quickly if there's too much culture. If they are at optimal temperature they are working super efficiently. While cheeses do need to be allowed to sit before brining in order to continue building more acidity, too much time could be a cause of over acidification. Remember, brining is going to significantly halt the progress of acidity, but if you've already passed the point, then it's like missing your exit ramp, except here you can't easily take the next one and double back. Something I like to do is add the cultures when the milk is cold, then I don't have to wait the extra ripening time as suggested in many recipes. I can't say if this is the best practice, but it works for me. So, look at your recipes to see where or what factors you can change to keep acidity in check. Also, best only to change one factor at a time to see it's affect, and not over do it.
