Hi Sarah, There are a wide range of people here and just as wide ranging experience. But the first thing is don't panic !
. Its just cheese... Just looking at this entry and going back to basics and I've had the very same issues. So... Lets start. And sorry if this sound simplistic - you have made cheese before but I think couple of things might help.
Temperature controlThere is a thing call temperature inertial - same concept as physical inertia. The tendency of a substance to stay the the same temperature until enough energy is applied to make it increase and the other is it requires something to happen to make it stop and in this case milk has a very different inertia that water. I know this might sound basic but if you remove the heat source instantly you stop adding energy and the temperature remains as is it and in a vacuum will stay the same temperature for a very long time. But it never is really removed instantly. There is aways residual heat and therefore can increase past the point you remove it at. How does this affect me making cheese ??
It has to do with the heating method. Direct heat - straight on the hob and indirect heat - like a double boiler or sitting a smaller pot in a larger one. The direct heat is fast but scorches the milk if not careful and due to the lag in instruments can be difficult to stop exactly on the required Temperature - hence moves past the required temp. Where indirect is slower but has more inertia, meaning the if you just measure the milk temperature and turn the heat off - and you leave the pot in the water - it will, depending on the size move the milk temp 2-4 degrees past whenever you turned off the heat source. Induction is the same though a lot less difference, it still occurs.
Milk quality: as you have already discovered is paramount - you can't make good cheese with bad milk
.
Milk Handling: Pasteurisation will cause damage to the milk, no matter how they do it. That said, LTLH (Low Temperature Long Hold) is the gentlest form and still be legally called pasteurised BTW the Mt Crawford milk sounds wonderful and they are using LTLH pasteurisation.
Calcium Chloride: Any milk under gone any pasteurisation should have this added as it helps with curd formation - you don't need alot 1/8 teaspoon in 8-10 Litres (sorry I'm metric) = appox 2 Gallons. It will help. If you find raw milk supplier you can ommit this.
Cultures: find out what the culture temperature ranges work at they are all different: some only have a narrow band to work in for example my Meso stops at 38 Deg C but my Thermo doesn't really start until 32- 34 deg C. This is important because cheese making doesn't happen without acid (Lactic Acid in this case)
Is this too simplistic ?? Not sure where you are at, because the 'Clean Break' is an important condition for the curd to reach.
-- Mal