Quickly for thoes who dont know Quark is the traditional soft cheese of central Europe. It is softer than cream cheese, but more dry than sour cream. It is favored by many since it is more lean than either cream cheese or sour cream.
You want to use Quark with out rennet. Rennet (pronounced /ˈrɛnɪt/) is a natural complex of enzymes produced in any mammalian stomach to digest the mother’s milk, and often used in the production of cheese. Rennet contains a proteolytic enzyme (protease) that coagulates the milk, causing it to separate into solids (curds) and liquid (whey). The active enzyme in rennet is called rennin or chymosin (EC 188.8.131.52) but there are also other important enzymes in it, e.g., pepsin or lipase. There are non-animal sources for rennet substitutes.
1 gal of milk (I take 2% type milk)
buttermilk (smallest unit is 1 quart; the culture differs from brand to brand)
Open the jar of milk (needs to be fresh at that time) and replace about half a cup of the milk with buttermilk. Mix gently to distribute the buttermilk culture throughout the milk. Close cap onto the gallon container (jar) as is and keep container in a warm spot (somewhere in between body temperature and 50oC). Wait for about 3 days until the culture has grown and the milk has clotted (looks cloudy). No stirring recommended.
As finishing step, remove most of the wey. To get prepared, place sieve (1 gal. size) into a large pot (for catching way from the sieve) and lay cotton cloth (thin dish towel) into sieve. Now you are ready for separating the quark from surplus wey. Transfer the batch of clotted milk and whey into this cloth covered sieve, cover with lid, and keep for about one day in a cool spot (nothing extreme). Sometimes you need to wait longer. You can choose how dry or moist you like your quark. Periodically remove the whey that has collected in the pot. The quark will remain in the cloth in the sieve. It will look white and moist. Very inviting.
Transfer the quark from the cloth into a small container. Keep refrigerated until consumption.
You don’t say what you want to cook and how you are adding quark…?
Quark is very like sour cream, so it will “separate” if added to hot liquids such as gravies, sauces, soups, etc. and because there is more bulk in quark than in cream (quark is the first stage of cottage cheese making) that is why it is not usually used in the same way as sweet or sour cream. Nor is it usually used in in quite the same as cream…
Quark is usually not cooked at all or when it is cooked, it is in such things as cheese cakes, pastries and breads (it is used as raising agent in some European baking).
On the whole, I would say that if you are trying to use it in any hot “liquid” (as it were) you need flour to “bind” the quark before adding it, much as you would when making a roux-based sauce. You may alternatively try beating the quark and adding some of the liquid very slowly until you have the consistency you need.
Like whenever cream has “separated” or “curdled” when added to a dish, you learn it must not be boiled (just gently heated) but if it does separate, a good old whacking with a whisk should solve the problem.
Sorry not to do better, but without knowing what you are really up to…. LOL! Hope this helps anyway!
Do not let it get to boiling point.