There are a variety of micro-organisms that make their home in milk. Different ones (and there are several from around the world) prefer different temperatures. Most of them are very beneficial, and when a large enough number of them are introduced into milk of their preferred temperature range, they will “culture” that milk and become dominant.
If you want to make yogurt, for example, you can buy a yogurt machine, boil your already pasteurized milk, and follow their directions…OR, you can go the home-made route, with no two batches quite the same, and all delicious. If you can procure raw fresh milk, so much the better; if not, whole organic milk that is not homogenized is second best. Many folks can only find whole organic milk: still cheaper and more rewarding than store-bought.
Making yogurt: bring one quart of whatever milk you have (goat, sheep, cow, some folks are even trying coconut) to 100 degrees F in a glass or stainless steel saucepan. Use a thermometer that is accurate and able to be dunked into the milk. Pour the warm milk into a clean glass jar (mason works great) and add 2 tablespoons of your favorite store-bought yogurt (but make sure there is NO sugar added, and that the yogurt is guaranteed live). Be sure to leave a good inch or so at the top for expansion. Close the lid tightly and shake well to disperse the culture throughout the milk. Do not shake again ! Yogurt likes to be “left alone.”
Now here it gets interesting….Almost everything I’ve read about yogurt claims that you must culture at fairly high temperatures: not in my experience! Yogurt seems to develop just fine in the 100 to 105 degree temp range, which can be in an oven with a pilot light, a super sunny window in a greenhouse, or a cooler with a heating pad…this is where you get to play Junior Chemistry Set and discover how to keep your culture in that temperature zone for approx. 6 to 8 hours….and yes you can go higher, but if you are using raw milk, your enzyme potential will drop every degree until you hit 118 at which point the enzymes present in raw milk are destroyed. The amount of time it takes can vary, and so the first few batches are experiments: watch for the tell-tale thickening of the milk as you GENTLY tip the bottle to see if it has coagulated yet. Commercial yogurt is often full of gums and powdered milk to make it thicker. When done, put into the fridge, and in a few hours it will be “set” and ready to use. Do NOT shake! You will lose the natural structure of the yogurt, and it will get “runnier” if you do.
Making kefir: bring one quart of milk to between 75 and 80 degrees F (and continue as above for yogurt). You can either get the kefir grains (which I’ve never done) and follow their directions or you can get a packet of kefir starter and follow their instructions as to how much to use for one quart. I started with a packet of kefir starter about 12 years ago, and have kept it going by using 2 Tablespoons of the previous batch to start the next batch (which is how you do yogurt once you get it going). Most commercial kefir has sugar in it (and gums, etc.) and I’ve never used it as a starter.
Kefir is actually easier than yogurt because it likes “room temperature.” That ideally means between 75 and 78 degrees F (don’t go below 70 or above 80 degrees). Find a spot that stays that temp for 24 hours…yes, 24 hours. In the winter I put wrap my kefir in wool or down and put into a cooler at night. The kefir is done when it “coagulates” but it will always be a bit “runnier” than yogurt. If you get the culture a little too hot, it may separate into “curds and whey.” No problem! The curds are like cheese and the whey can be used to make sauerkraut and kim chi, which is next week’s blog. Sometimes ny kefir is “sparkling” and very tangy, and sometimes it is smooth and creamy. Part of the fun is that each batch is a wee bit different.
This is a great activity for children of all ages: the alchemy of micro-organisms, and the vagaries of each day. hope you enjoy!