What Milk to Use:
Kefir works best with whole milk from cows, goats or sheep. You can try kefir in low-fat milks, but grains may need to be refreshed in whole fat milk for long-term vitality. Use raw or pasteurized milk, but be sure to avoid ultra-high temperature pasteurized milks (always labeled UHT).
Making More or Less Kefir:
You'll need about a teaspoon of grains to ferment 1 to 2 cups of milk. Your grains will start to multiply over time, allowing you to ferment more milk if you choose. Maintain a ratio of about 1 teaspoon of grains to 1 cup of milk. If you have more than 1 teaspoon of grains in a single cup of milk, take note that fermentation time will quicken, likely resulting in stronger and more sour flavors, or a separation into curds & whey (see below). Share an overabundance of kefir grains with friends, and adjust your ratios or fermentation times accordingly.
What to Do if Your Kefir Separates:
Sometimes kefir will separate into curds and whey. This is an indication that the kefir is fermenting the milk very quickly. To remedy the separation, shake; whisk; or blend the kefir for a more desirable consistency, or try making kefir cheese. To avoid separation in the future, adjust the grain to milk ratio (discussed above), remove the grains earlier or ferment in a cooler location.
Taking a Break from Brewing:
To take a break from making kefir, simply transfer the grains into a fresh cup of milk, cover with a loose lid and refrigerate for up to a month. (Grains may be sluggish post-refrigeration and take a bit longer to ferment your first couple batches of kefir.)