Spoilage of Uht milk pouch
I have a Uht milk processing and asepsis packaging unit. I am experiencing a kind of spoilage of packets which is not characterized by puffing/bloating/inflating packets. The packets seem to be good. But the milk when poured out of a newly cut packet and heated on the stove ferments and starts curdling. It happens in 2 or 3 out of every 20 packets and so i cannot decide whether it is the fault of the machine or something else.
According to one of the dairy manufacturing experts in our department it appears it could be an issue with non-gas forming thermoduric spore-formers. "If these microorganisms are producing slight levels of acid but more importantly some levels of proteolysis this could cause sufficient destabilization of the casein micelle such that on heating the product further exposure to the inversely soluble ionic calcium might result in coagulation" (verbatim). It is very likely that this issue is not directly a result of the process or the packaging. It is most likely to be traced back to the initial milk supply. Some sampling of the milk supply to identify the potential source of the thermoduric spore-formers is the most likely avenue towards finding a resolution to this quality issue.
Here's another contribution with steps to solve the problem:
Alvaro, I saw this problem before and the reason was exactly what Howard suggested. I agree that most likely the source of the high resistant spores (HRS) is the raw milk. However, biofilm formation by HRS on heat exchangers, pasteurizers, and gaskets is also very common. If this type of spoilage is common at this facility, I suggest the followings to control this problem: 1. Milk bactofugation. 2. Visual inspection of the production line for formation of deposits/biofilm. 3. Milk should be held for at least 2 hour after pasteurization and before the UHT treatment at temperatures not lower than 25 C. 4. Swabs should be taken from the production line to identify/exclude sources of contamination other than raw milk. 5. Bacteriological analysis of milk samples at all production steps especially the aseptic tank prior to filling. 6. Milk should be held for at least 10 days after manufacturing. Samples should be stored at 30 and 55 C. During this period, any slight drop in pH (even 0.1 unit) or change in taste will indicate microbial growth. I hope this helps,