Sterilize all of the equipment you'll be using; wooden spoons (not metal!), pot, and jars that you'll be storing your homemade yogurt in. Although we're using yogurt as our starter here rather than a probiotic or starter powder, it's still best to have everything sterilized so there is no bacteria in your pots/jars competing with the yogurt cultures.
To sterilize them simply wash in hot, soapy water thoroughly and then leave to dry completely. For the jars, I like to do this by placing the items onto a baking tray, in the oven at around 160ºC/325ºF for 10 minutes.
To begin making the homemade yogurt, start by heating the milk over medium heat until it reaches 80-85ºC/175-185ºF (if you don't have a thermometer, switch off the heat right before the milk starts boiling).
Set it aside to cool down till 40-45ºC/105-115ºF (if you don't have a thermometer, you can dip your pinkie in the warm milk and try to keep it there for 7 seconds before it starts to hurt. Be careful though! and touch the mixture lightly before plunging your finger into it- so you don't get burnt.)
It is necessary to cool down the milk so that the live cultures can survive - so don't rush this process.
Once it is cool enough, add the yogurt and stir it with a wooden spoon.
Transfer to a clean, sterilized glass container.***
Wrap the jar in a warm tea towel or blanket and keep in a warm place for a minimum of 6 hours (or up to 12). I usually keep mine in my oven, switched off.
Once the incubation period is over then you can transfer it to the fridge and leave to set for a further 12-24 hours and then pour off any liquid whey that may be sitting on the top.
For Greek Yogurt
Rather than transferring it to the fridge, you can now strain the yogurt. Using a muslin cloth, cheesecloth, or nut milk bag ( my preferred, low-mess option), transfer the yogurt into the nut milk mag and hang it above a bowl to drain. You can do this by hanging it from your kitchen faucet, a kitchen cabinet handle, or using a large jar.
The more you strain it, the thicker the yogurt will become- I suggest testing it after 3-4 hours and then leaving for longer, if preferred.
Transfer the greek yogurt to a sterilized glass jar and place in the fridge.****
How To Store:
Homemade yogurt will keep well for between 1-2 weeks in the fridge. Always use clear utensils to remove yogurt from the jar as any bacteria can affect the potency of the starter when re-using it.
Remember to keep a few spoonfuls of the yogurt behind to use as your starter for your next batch!
* I used full fat raw unpasteurized milk for this particular batch ( in the images), but you can also use pasteurized milk or low-fat milk (but the yogurt will not be very thick), or even half and half. ** You can also use yogurt starter powder.*** The strained whey is full of protein and goodness and can be added to a variety of baked goods, into a smoothie, as part of homemade stock and in soups and stews.**** If you are making a bigger batch, you can store them in different smaller jars and this will make them last for longer (as long as the jar is unopened).