This from a fellow dairy woman:
Hello! My husband and I just finished watching your dairy class on STS along with Carolyn’s. We had a question about starting cultures and couldn’t figure out how to contact you to ask so thought maybe here would work? Our question is this… You mentioned needing fresh milk, so does that mean it cannot be milk that has been in the fridge for a few days? And you want the milk and cream all still in it too, yeah? Not with the cream skimmed off or anything?
Hi, Ashley! Good to hear from you.
The fresher the milk, the fewer airborne bacteria and yeasts it will harbor, and the greater the proportion of native lactobacilli in any ferment, if you follow us. That is to say, when the milk is fresh, it has been inoculated with lactose-converting bacteria from the animal’s teats; subsequently, it is also inoculated with airborne and surface-borne bacteria and yeasts. It is the former assortment of biota, at least primarily, which the dairywoman wants to propagate for cheesemaking and other food purposes; so the fresher the milk she cultures, the higher the proportion of native lactobacilli.
As far as the cream content, our experience and our research both indicate that the milk used can be skim milk – that is, the fat content can be low – without detriment to the results. We generally make our cultures with our own hand-skimmed (dipper-skimmed) milk. Milk like this – gravity-skimmed milk – is usually at least 12 hours old (the time generally allowed for the cream to rise), so it is not absolutely fresh, because the air and surface-borne bacteria it picked up after milking have had time to reproduce. It is possible, even probable, that these surplus biota play a positive role in the living communities that make delicious cheeses and other dairy products.
Machine-separated milk, on the other hand, has to be assumed to be bacterially inoculated by its contact with the many surfaces of the separator apparatus, which are pretty defiant of deep cleaning, and which, over time, harbor lots of interesting – but perhaps not delicious – secondary colonizers; but since machine-separation happens with perfectly fresh milk, this extra cast of characters has little time to reproduce before you, the dairy woman, provide the native, desirable lactobacilli with their favorite growing conditions, giving them the edge in reproduction.
Does this help? – Beth