Quark v Bacteria??
I have been given a recipe for making Quark. Its just full cream milk mixed with butter milk (or sour cream) left in a warm place over night, then strained for a few hours & only then refridgerated.
So my question is why is it ok to leave milk out to make Quark and is safe to eat. But if i leave milk out over night it would make me ill to drink it??
No need to kill bacteria. You WANT bacteria, if you kill the bad, you kill the good. The good will outweigh the bad almost every time unless you forget about it for days. There are different recipes and directions for the same things though. If you are using a trusted recipe, don't worry at all. If you are using pasteurized milk and it goes bad, you will know about it before it reaches your mouth :) Soured pasteurized milk stinks in any form, soured raw milk will smell clean and tangy and if it doesn't curdle, toss it. Cultured dairy is easy to tell the *good from the bad* right away.
I make all KINDS of cultured dairy products at home (kefir, butter, yogurt, sour cream, quark, cream cheese, ricotta, etc). It is easy. Try different recipes and techniques to experiment.
I have made quark and sour cream (very similar, quark has a drier curd) and you don't need to heat the milk for most of these recipes but you need to have a warm place to culture it.
When I culture in Mason jars, I wash in hot soapy water, rinse with hot water then culture in the warmed jar (gives it a head start).
Raw milk is easier to work with than pasteurized milk (faster better tasting curd) and don't use "ultra"pasteurized anything because either it won't take or it tastes inferior.
The acid often keeps it safe to leave on the counter for 24 or more hours. I prefer lemon juice to vinegar, buttermilk to lemon juice.
Coffee filters inside a stainless basket strainers work well to dry out your product.
I'm a little surprised you're not told to heat the whole-fat milk before starting to kill off any unwanted bacteria.
Either way -- you're inoculating the milk with the microorganisms from the buttermilk or sour cream (it's very important to use buttermilk or sour cream with live and active cultures) -- thus you're giving a serious headstart to the beneficial bacteria that you WANT in your quark.
If you leave milk out overnight, you have no idea what is actually growing there...and the lack of a sterilization/inoculation step means that you have a very good chance of growing some pretty nasty critters in the milk that you've left out overnight.
It's all about population control...but a very fair questions.