Making yoghurt at home is simpler than most people expect. The process has two variables that matter – temperature and starter culture – and once you understand why they matter, the rest is just following a straightforward sequence of steps. Homemade yoghurt is milder than commercial yoghurt (you control the fermentation time and therefore the acidity), contains more live cultures (commercial yoghurt is often heat-treated after fermentation), and costs a fraction of the commercial equivalent. It’s also one of the most satisfying things you can make in a kitchen because the transformation is genuinely remarkable: warm milk and a spoonful of culture become yoghurt overnight without any further intervention from you.
What You Need
1 litre of whole milk (fresh pasteurised gives the best result, though UHT works too), 2 tablespoons (40 ml) of plain yoghurt with live cultures as your starter (any shop-bought plain yoghurt that lists live cultures will do), a thermometer (a digital probe thermometer is best; a jam thermometer also works), a heavy-based saucepan, a clean jar or container with a lid, and a way to keep it warm for 6 to 10 hours (options below).
The Method
Heat the milk in a heavy-based saucepan over medium heat, stirring often so it doesn’t catch on the bottom, until it reaches 85°C. Hold it at that temperature for 10 minutes, or up to 20 minutes if you want it extra thick. The heat changes the whey proteins so the yoghurt sets firmer and is less likely to weep whey later. Take the pan off the heat and let it cool to 43°C. This is the number that matters most. The cultures work best at around 42 to 46°C, and if the milk is hotter than about 46°C when the starter goes in, you risk killing them.
Spoon a cupful of the warm milk into a small bowl, whisk the starter into it until smooth, then stir that gently back through the pot. Pour into your clean jar or container and put the lid on. Now keep it warm and undisturbed at around 43°C (the ways to do that are below). Most batches take 6 to 10 hours. Start checking at about 5 hours: when it’s set (tilt the jar and it holds together rather than sloshing), it’s done. The longer it sits, the tangier it gets. As soon as it has set, move it to the fridge, which slows the cultures right down and stops it getting more sour.
Straining for Thickness
Fresh homemade yoghurt is softer than most shop-bought yoghurt. To thicken it, line a sieve with a double layer of cheesecloth or muslin and set it over a bowl, leaving a gap underneath for the whey to collect. Tip in the yoghurt, cover, and leave it in the fridge. The longer it drains, the thicker it gets. For Greek-style yoghurt, give it at least 8 hours, or up to 24 if you want it really thick. Drain it longer again and you’re on the way to labneh. The liquid that drains off is whey. Keep it for bread, pancakes or smoothies rather than tipping it out.
Saving Starter for the Next Batch
Before you dig in, set aside 2 tablespoons of the finished yoghurt in a small sealed container. That’s the starter for your next batch. Use it within 5 to 7 days, while the cultures are at their liveliest. Each batch can seed the next for a while, but the cultures lose strength over time, so start again with a fresh tub of plain live yoghurt every 5 or 6 batches, or sooner if it stops setting well. Spare starter can be frozen.
Choosing Your Milk
The milk you start with shapes the yoghurt you end up with. Full cream dairy gives the thickest, richest result because the fat and protein both contribute to body. Skim milk will set, but the yoghurt is thinner and sharper. To firm it up, strain it, or whisk about a quarter of a cup of skim milk powder into each litre of cold milk before you heat it (added to hot milk, the powder can turn stringy). Fresh pasteurised milk gives a cleaner flavour than UHT, though UHT is convenient and lets you skip the 85°C step, since it has already been heated hard during processing. Just warm it to 43°C and carry on. For your first few batches, steer clear of ultra-filtered or lactose-free milk, as the altered sugars and proteins can give an unpredictable set.
Plant milks are a separate story. Soy, oat, coconut and almond milks do not contain the lactose and casein that dairy cultures feed on and bind to, so they will not set the same way. You can make plant-based yoghurt, but it needs a starter made for plant milk and often a thickener like tapioca or agar. If you want plant yoghurt, treat it as its own recipe rather than a swap.
Keeping It Warm: The Methods Compared
The one thing that makes or breaks a batch is holding a steady warmth of around 43°C for the whole ferment. A few ways to manage it, from least to most reliable:
- Oven with the light on: wrap the jar in a thick towel and sit it in a turned-off oven with just the interior light running. In most kitchens the light gives off enough gentle heat. Free, but check your oven actually holds the warmth.
- Esky or cooler box: sit the jar in an esky next to a jar of hot water and close the lid. The insulation holds the warmth for hours, which is handy in a cold kitchen.
- Thermos flask: pour the cultured milk straight into a wide-mouth thermos. It holds temperature beautifully, though you cannot check the set without tipping it out.
- Yoghurt maker or multicooker: a purpose-built maker, or the yoghurt setting on a multicooker, takes the guesswork out entirely. If you make yoghurt often, this is the easiest path to a consistent result.
Troubleshooting
It didn’t set. The usual causes are heat, culture and warmth. If the milk was still above about 46°C when you stirred the starter in, the heat will have killed the bacteria. If your starter was old or had no live cultures, there was nothing there to do the work. And if the spot you left it in ran too cool, the cultures will have barely got going. Use a fresh plain yoghurt that lists live cultures, let the milk cool to 43°C before adding it, and keep it warm while it sets.
It’s too thin. Homemade yoghurt is softer than shop-bought, so some of this is normal. For a firmer set next time, hold the milk at 85°C for the full 20 minutes, which firms up the proteins. Straining will thicken any batch.
It’s too sour. Sourness comes from time. The longer it ferments, the more acid the bacteria produce. If your yoghurt is sharper than you like, start checking from about 5 hours next time, and get it into the fridge as soon as it has set.
It’s grainy or lumpy. This usually means the milk got too hot, or it was stirred too hard once the culture went in. Heat gently, stir the starter in softly, then leave it alone to set.
It’s stringy or slimy. A ropy, stretchy texture points to a culture that has drifted over many reuses, or a stray contaminant. Start again with a fresh commercial starter and clean equipment.
Common Questions
Is homemade yoghurt safe to eat? Yes, when made with pasteurised milk and clean equipment. Heating the milk and the acidity the cultures produce both help keep unwanted bacteria out. Trust your senses, though. If a batch ever smells off, looks mouldy, or tastes wrong, throw it out.
How long does it keep? Stored in a sealed container in the fridge, homemade yoghurt keeps for one to two weeks. The flavour sharpens over that time as the cultures stay slowly active.
Can I flavour it? Yes, but add anything sweet or fruity after the ferment, not before. Sugar and fruit during fermentation can throw the cultures off. Stir through honey, vanilla, or fruit once the yoghurt has set and chilled.
Sources
The method on this page is adapted from the tested recipes published by University of Illinois Extension and America’s Test Kitchen, and cross-checked against Washington State University Extension and Matthew Evans at SBS Food. The straining times follow America’s Test Kitchen’s guide to Greek-style yoghurt.
