Greetings O.C.,
The science behind the bitterness is that you may have an excess presence of hydrophobic peptides of low molecular weight (< 6kDa). Some of the main reasons for this are high acidity rate, use of excess rennet/starter culture and low pH. Cheeses with low salt content or low lipid content are in general more vulnerable to this effect.
The things that can cause these phenomena can vary but the main examples are:
1) High plasmin presence in raw milk, which is a heat resistant enzyme, that degrades β-casein. Same effect can be caused by higher than normal rennet concetration.
2) Environmental microorganisms (non-starter microflora) that could be present during manufacturing (eg Lactobacillus plantarum and Lactobacillus casei).
3) Higher proteolysis than normal due to excess use of starter culture, which leads to higher production of low mol. weight peptides.
4) Possible cross-contamination from yeast/mold from the environment that affects the cheese after manufacturing is a bit less likely, but you can't totally excluded it if none of the above contribute to the problem.
Look also for any changes that may have happened recently (if any) in the manufacturing process, raw materials (not milk), new personnel (maybe not well trained) and lastly the milk itself cause its composition can often vary due to season/diet etc.
There are quite a few posibillities to explore, but I hope they help you get started.
Regards!
Edited by Evans X., 21 April 2022 - 08:34 AM.
