You can prepare Milk Kefir quite easily. The ratio grains to milk is 1:10.
100 grams grains needs 1 liter of milk
50 grams a 1/2 liter of milk
Put the milk with the grains in a jar with a lid. Don’t use a cloth or gauze, because then you have a higher risc of contaminating it with a foreign bacteria. If you leave the jar on the countertop you will see a result within 24 hours. If you think this is to fast, you can leave the jar in the refridgerator, the proces will be slower.
The fermention proces will go faster as your grains grow and the ratio to milk is going upwards. The proces will go slow if you do not have enough grains.
You can use all sorts of animal milk: cow, goat, full cream, semi skimmed, low fat, raw milk… Just try which one you prefer.
The Kefir does enjoy a little fat every now and then. The grains will flourish in some (whipped) cream and in the end you will have a delicious sour cream!
With some adjustments you can also use non animal milk like soy milk. One of the characteristics of soy milk is that it has no lactose, the food of Kefir. You will have to substitute the lactose by cane sugar (often soy milk allready contains cane sugar). The soy milk Kefir drink will not be as thick as for example cow milk Kefir.
Tip: use glass jars, you can clean them easily and plastic will form a rough layer after a while, which is not only unhealthy but also really hard to clean. Do not use metal! Not even to stir, the Kefir does not respond well to metals.