Under refrigerated conditions, Gram-negative rods that are able
to produce under such conditions ( psychrotrophic/cold-loving
bacteria ) usually predominate, especially Pseudomonas spp.
This is especially so when the milk has a high initial infection
of these bacteria and the milk is stored for 2-4 days before
pasteurization - which is often the case these days, where milk
is mostly being picked up from farms every second day only.
This deterioration also often influences the final products made
from such milk, because although bacteria will mostly be killed
by pasteurization, some produce exo-enzymes that survive
pasteurization and even the UHT (Ultra High Temperature/Long
Life) process in some cases.
An example of Pseudomonas attacking dairy products happen a lot
with cottage cheese. Pseudomonades are widely distributed and
aerobic. They tend not to need much carbohydrate, which help
them a lot in attacking cottage cheese, because most of the
lactose has been removed in the cheese making process. They live
very well on high-protein foods like cottage cheese producing
slime, pigments and odours. They also prefer high water activity
( high moisture), which makes cottage cheese pretty much the
ideal food considering everything that has been said.
Many Pseudomonas spp. are psychrotrophic ( cold-loving )
bacteria although they will grow a lot faster from 15 degrees
Celsius to temperate.
Thus a temperature shock during transport for example will give
them a big boost - to cause even more destruction.
About the author:
Leon the Milkman is the owner of www.LeontheMilkman.com and www.dairy-info.org from where he gives a dairy dictionary and cheese tasting terms guide to new members.
