The only 2 Ingredients you’ll need:
Pasteurized milk. Whole milk makes the creamiest, thickest yogurt, but skim or low fat will work fine too.
Any plain yogurt with live and active cultures, or pre-packaged yogurt starter
There are many other things you can add, such as flavors, fruit, granola, sweeteners, and stabilizers, all of which may or may not come in a healthy form. But milk and yogurt starter are the only ingredients you’ll ever need to make yogurt in its simplest, purest form. You can always add whatever toppings or sweeteners you like later, or just enjoy it plain and pure!
Once you make one batch, you can use some of that yogurt as a starter. If you made Greek yogurt, you can even use the yogurt whey (the liquid that strains out) as a starter. It works just as well as solid yogurt, and as a liquid, is even easier to add to your new batch than actual yogurt.
The equipment you’ll need:
If you don’t have an instant pot, you can use a double boiler (preferred) or single pot to boil the milk and an automatic yogurt maker for the fermentation process. If you are working without an Instant Pot or yogurt maker, you can still use any warm and insulated area. But the most foolproof and reliable way to maintain perfect conditions throughout the fermentation process would be to use an instant pot or electric yogurt maker.
Sous Vide function on Instant Pots
While having a yogurt function should be enough to make great yogurt, I prefer an Instant Pot with both sous vide and yogurt functions.
This is because heating the milk for 20-30 minutes to 180° Fahrenheit (83° Celsius) before adding the starter helps activate more of the otherwise inactive proteins found in milk. This helps the yogurt come out thicker and also helps destroy any harmful bacteria which may be in the milk. Many instant pots have a yogurt function which will boil your milk to 180°F but will not maintain that temperature for 20-30 minutes. What's great about the sous vide function is that it allows you to set an exact temperature for 30-minute increments. Some newer instant pot models even allow you to set a custom temperature in other functions as well. The user guide for my instant pot actually suggests running the regular yogurt function’s BOIL cycle twice. But I find the sous-vide method to be much easier being that I only need to set it once and the temperature stays steady for 30 minutes.
If you use a regular pot without a double boiler, be sure to constantly stir the milk while monitoring the temperature so it shouldn’t scorch.
In all cases, you’ll need a food thermometer. You’ll be using it to see when the milk is cool enough to add the yogurt starter (otherwise the heat will kill the bacteria). If you are using a double boiler or single pot to boil the milk, you’ll want to use the thermometer to help you know when your milk has reached 180°.
If you have an instant pot with sous-vide, simply add the milk to the pot, plug it in, and press the “sous-vide” button. Press the + and – buttons until it shows 00:30, press the △ or ▽ until it displays “180°F” and then press “start”. The countdown will begin once the milk has reached the target temperature of 180°F. At that point, the heat will automatically turn off and the pot will beep. If you’re in a hurry, you can simply press “cancel” after 20 minutes and start the cooling process.
If your instant pot does NOT have a sous-vide function, use the BOIL setting in the pot’s yogurt function. Press the “yogurt” button, press the △ or ▽ until it displays “BOIL” and then press “start”. If you’d like to run the BOIL cycle twice in a row for a thicker result, simply restart the BOIL process as soon as the first one is finished.
Please note that depending on your instant pot model, the instructions may vary slightly, so be sure to consult your user manual if you aren’t sure.
If you are using a pot or double boiler, add the milk and set a medium flame. Do not leave the pot unattended as the milk may boil over. Keep stirring the milk slowly while checking the temperature. When it reaches 180°F, lower the flame enough to allow the temperature to hover at or slightly above 180°F. Ideally, for the thickest possible yogurt, you should maintain this temperature for 20-30 minutes. If this is too difficult, you can turn off the flame and begin cooling the milk as soon as it reaches 180°F.
STEP 2: THE COOLING PROCESS
The shortest and safest way to cool down the milk is by bathing the pot in a sink full of cold water. Alternatively, you can just leave it to cool by itself.
As the milk cools, a film will form on top of the milk. This should be removed before you add the starter. If you’re afraid that pieces of the film broke up into the milk, you can simply strain the milk before starting the fermentation process. I use my Greek yogurt strainer to strain the milk every time I make yogurt. This helps me be certain that there won’t be any unappetizing pieces of dried milk in my yogurt. After I pour the milk into the strainer, I also wash the pot insert if I see dry or burnt milk particles on the bottom.
STEP 3: ADDING THE STARTER
When the milk has cooled down to around 110°F, you can begin mixing in the starter.
If you’re using yogurt as a starter, pour a little milk into a clean cup, mix the yogurt into the milk, and then slowly whisk the mixture into the rest of the milk.
Use around 1 heaping tablespoon per half-gallon of milk (a bit less for a quart). This amount doesn’t need to be precise to the milliliter, but don’t overdo it, because the bacteria can crowd itself out and ruin the taste/texture.
If you’re using a store-bought starter, simply follow the instructions on the package and add the amount you need based on the amount of milk you’re fermenting.
If you’re using yogurt whey simply mix it into the milk. Use around 1/4 of a cup per half gallon.
When using an Instant Pot, simply close the lid, press the “yogurt” button, press the △ or ▽ until it says MED or displays a default time of 8:00 (Hours), then press start. You can add more time for more tart yogurt.
When using an electric yogurt maker, simply pour the milk into the machine (or jars if it uses those), cover it, and start the fermentation according to the manufacturer’s instructions.
If you don’t have an instant pot or yogurt maker, there are still other ways to keep the yogurt warm while it ferments. You can place the pot into a cooler with bottles of hot water or a bath of warm water around the pot. Another idea is to use a heating pad on the pot of milk. If your oven uses a pilot light, that may be another way to keep your yogurt at the correct temperature (108-115). In my opinion, though, the ideal and most reliable way to ferment is to use an instant pot or electric yogurt maker.
When the yogurt is finished, it will have a consistency somewhat similar to Jell-O. Refrigerate promptly and enjoy once it’s chilled. Homemade yogurt may be a bit lumpy, this is natural. If you like it smoother, use the Greek yogurt method below to strain some of the whey, then gently whisk the yogurt until it’s smooth.
Homemade yogurt should last about 2 weeks in the fridge and may taste best during the first week. You can also freeze yogurt for up to 2 months.
To make your yogurt “Greek” it is easiest done with a dedicated Greek yogurt strainer. Simply pour the finished yogurt in, and then refrigerate for 5-24 hours depending on how thick you want the yogurt to be.
If you don’t have one you can still strain the yogurt using a cheesecloth and regular strainer. Line the strainer with cheesecloth and pour in the yogurt. Place it over any pot or container to catch the liquid as it strains. Or, if you’re dealing with a small amount, you can even use a funnel with a paper coffee filter, also with a container or bowl to catch the whey.
You can save the whey to use as a starter for your next batch, but use a new store-bought yogurt with live cultures or freeze-dried starter after 4-6 batches because bacteria activity slows down just a bit with each batch when you re-use homemade yogurt or yogurt whey as a starter.