I looked at your notes and had some problem with the Canadian French so let me answer your question this way: When you add a DVS culture to warming milk it takes about 30 minutes to hydrolyze ("wake up") the culture. Then it starts to divide and divides roughly every 20 minutes. Thus, if you have one "unit" of active culture when it is hydrolyzed, you have 2 units 20 minutes later, 4 units 20 minutes after that and 8 units after an hour. After two hours you have 64 units. All this is stylized but illustrates the point I'm about to make which is this: The acid production rate assuming sufficient lactose is proportional to the amount of culture present and pH is proportional to the amount of acid present. It takes a full two hours to get to 64 units. After the next hour this increases to 512 units or roughly eight times as much culture producing acid after three hours compared to the amount producing acid after two hours. Boiling this down the acid production increases exponentially and the pH drop accelerates downward in a similar fashion.
The process of renneting is one of starting to separate the curds and whey: Cut the renneted milk and you have two phases: the semi-solid curd that still contains a lot of whey and the whey itself. The culture tends to stay with the curd and so the pH drops faster in the curd than the whey. At this point you should only measure the pH in the curds as this is when your goal pH lies. To do this you should grab a small handful of curd and squeeze it to remove the whey. This is then "smushed" around the electrodes of the pH probe to get a reading that represents mostly the curds rather than an average of the curds and whey. Got it?
Do it this way and you'll get better consistency and be able to troubleshoot problems. Other things being equal, pH and final moisture content determine the characteristics of the completed cheese.
