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Stockpot large enough to easily accommodate two litres of milk
Whisk or wooden spoon
Thermometer (optional, but extremely helpful)
Glass containers for culturing and storing the yogurt
Bowl for whisking yogurt starter
Tools for incubation according to incubation method: heating pad and towels, cooler or large stockpot, food dehydrator, etc.
2 litres (approx. 8 cups) milk
1/2 — 1 cup yogurt starter culture — this can be a cup of yogurt from your last batch, a cup of plain store-bought yogurt with no gelatin or other additives, or a packaged yogurt starter
There are four parts in the yogurt-making process: warming the milk, cooling the milk, inoculating it (culturing it), and incubating it.
Sterilize: Make sure all equipment is very clean. If possible, sterilize your jars or containers in a pot of boiling water.
Place the milk in a saucepan or stockpot large enough to comfortably accommodate the milk with a bit of room for whisking. Preferably choose a heavy-bottomed pot with a lip, as this will reduce the amount of milk that scalds and will help make pouring the milk later drip-free.
Heat milk to 180-190°F, whisking occasionally, especially once the milk passes 160. (This is when it begins to foam and scald — latte anyone?) If you don’t have a heavy-bottomed pan and your milk does begin to scorch and stick to the sides of the pan, don’t stress about it. Just take a bit of extra care when you’re whisking so that you don’t scrape off any of the scalded bits into the milk — you can just clean them out later. Also, a note about why you’re heating the milk — regardless of whether you’re using raw milk or conventional milk, gently heating the milk in this manner physically changes the molecular structure of the milk proteins which will result in a decidedly firmer yogurt.
Once the milk has reached 180°F or so, cool it to approximately 115°F. [If you don’t have a thermometer, I’ve heard it said that the milk is cool enough when you can hold your (very clean) little finger in the milk for 10 seconds.] You can cool your milk in a number of ways; just choose which works best for you. an ice bath cools the milk quickly and safely place it in the refrigerator (if you’re doing a large batch, such as a gallon or more, this method is not preferable as it will heat the refrigerator too much as it cools) in the winter, you can cover it and place it outside away from pets, other animals, or anything that could knock it over or fall in it just cover with a cloth and let it sit at room temperature until it’s cool — this will typically take a few hours
Have your starter culture ready in a bowl. When the milk has reached approximately 112°F degrees, whisk some of the warm milk into the starter culture, then whisk the warmed culture into the entire pot of milk. After the mixture is mixed, pour the prepared milk into your containers.
At this point you have your choice of how to incubate it. The yogurt culture needs to sit at 108°-112°F degrees for 6-8 hours, so however you can come up with to keep it at that temperature should work just fine. (My sister even successfully set her jars outside for a number of hours covered with a towel when she lived in sub-tropical climes. That definitely wouldn’t work in my more northerly location!)
Here are some of the most popular methods:
Food Dehydrator: If you have a food dehydrator with removable trays, such as Excalibur, LEM, or Weston, remove all the trays, set your containers inside, replace the door, and set the temperature control for 112. Come back in six hours and your yogurt should have set perfectly! Note: don’t open the door unless absolutely necessary during the incubation time, as it may change the temperature inside the dehydrator overmuch.
Oven overnight: Preheat your oven to it’s lowest temperature — basically turn your oven control dial just until the indicator light comes on. If you’ve got touch buttons, set it as low as it will go. You just want the temperature to be around 112 without being much warmer than that. When the oven is preheated, turn the oven off, turn the oven light on, set your prepared containers in the oven, and leave them there for 6-8 hours — overnight is great. Remove them when the yogurt is thick.
Water bath: Set your prepared containers in a large pan with warm water as far up the jars as possible and cover with towels all around. Check the jars every couple of hours to make sure the water temperature hasn’t dropped. If the water is too cool, change the water to return it to the proper temperature. I used this method for quite awhile, but I found it to be a hassle, and it also disturbs the yogurt when you change the water, which can make the process not as effective. Remove the jars when the yogurt is thick after about eight hours.
Heating Pad: Set your prepared containers on top of a heating pad, invert a large stockpot over them, and cover the pot with towels. Turn the heating pad to “high” or “medium,” depending on your particular heating pad. Mine doesn’t get very warm, so “high” is definitely necessary. Also, be careful to note if your heating pad has an automatic shut-off feature. Mine turns off every half-hour, so when I use this method I have to make sure I turn the heating pad on again every 30 minutes. Remove the jars after 7-8 hours.
Yogurt Maker: This typically only works for a litre or so at a time, as yogurt makers tend to incubate in one-serving size cups (which is great if you’ve got kids and your mornings are rushed — just pass them a little cup with some fruit and whole grains and they’ve got breakfast!). Spoon your prepared milk into the yogurt maker’s cups, set the lid in place, and turn on the machine. From that point, follow the manufacturer’s instructions.
At the end of 6-8 hours, the yogurt should be somewhat firm and pull away from the side of the container with only a bit of whey (extra liquid). The yogurt will continue to firm up in the refrigerator, so for the best flavor and texture, refrigerate at least six hours before serving.
Yogurt Troubleshooting: If you’ve got too much whey, you likely incubated longer than necessary. If the yogurt is too thin, the temperature was too high or too low, the milk wasn’t fresh, or your starter wasn’t sufficient, either because you didn’t use enough or because the culture was old. Yogurt culture can degrade over time due to the introduction of foreign bacteria so using a fresh starter every few batches is recommended. So, now you’ve got a fridge full of inexpensive, delicious, nourishing yogurt! And even better, if you are able to do this regularly, it will become second nature and an easy part of your kitchen routine.