How much starter do I need for homemade yogurt?

Use 2–3 tablespoons (30–45 ml) of live plain yogurt per litre of milk, or one freeze-dried sachet per 1–2 litres per the brand's instructions. More starter is not better — too much (over 3 tablespoons per litre) causes grainy, overly sour yogurt because the bacteria compete for lactose too quickly.

How long does homemade yogurt last?

Homemade yogurt keeps 1–2 weeks in the fridge at 4°C / 40°F, though it tastes best within the first 7–10 days. It gets progressively more sour over time as residual fermentation continues slowly in the cold.

Can I use store-bought yogurt as starter?

Yes, as long as it lists live active cultures and keeps the ingredient list simple — plain yogurt without gums, starches, or heavy thickeners works best. You can re-culture from the same store-bought tub for about 5–7 batches before the culture weakens and needs a fresh source.

Why is my homemade yogurt runny?

The most common reasons are not heating the milk to 82°C first, incubating at too low a temperature, or not incubating long enough. Adding 2–4 tablespoons of milk powder per litre before heating can also help, especially with lower-fat milk.

Is homemade yogurt healthier than store-bought?

Homemade yogurt is fresher and typically has higher probiotic counts because it has not sat on shelves for weeks. It also contains no added sugar, thickeners, or preservatives. The fermentation process itself reduces lactose content by about 20–30%, which can help with mild lactose sensitivity.

Can I make yogurt with non-dairy milk?

Soy milk works best because its protein content is similar to cow's milk. Coconut and oat milk need a thickener — about 1–2 teaspoons of tapioca starch or agar per litre — and tend to produce a softer set.

Homemade Yogurt: How to Make It From Scratch — Ferment Calculator

Homemade yogurt is milk that has been fermented by live bacterial cultures — the same process that happens in a factory, just happening in your kitchen. The method is genuinely simple: heat milk, cool it, stir in a starter, and hold it warm until it sets. The result is fresh yogurt with no added sugar, thickeners, or preservatives, and a higher probiotic count than most store-bought tubs.

How yogurt fermentation works

When you add live bacteria to warm milk, the cultures — primarily Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus — feed on lactose and convert it into lactic acid. That acid is what thickens the milk into a gel and gives yogurt its tang.

The process reduces lactose content by roughly 20–30%, which is why even people with mild lactose sensitivity can often eat yogurt comfortably. Heating the milk first denatures the whey proteins (mainly beta-lactoglobulin), which produces a noticeably thicker, creamier set.

82°C / 180°F milk heating target

43°C / 110°F ideal inoculation temperature

6–12 hrs incubation time range

Which milk to use

Whole milk thickest, creamiest results — the best choice for beginners.

2% or skim works but sets thinner. Add 2–4 tablespoons of milk powder per litre to improve body.

UHT / ultra-pasteurized already sterile, so you can skip the heating step. Sets slightly softer; some makers still heat briefly for protein restructuring.

Raw milk ferments fine, but produces thinner yogurt because the proteins have not been denatured. Heat to 82°C anyway for best texture.

For non-dairy alternatives, soy milk works best thanks to its protein content (~7 g per cup). Coconut and oat milk typically need a thickener — about 1–2 teaspoons of tapioca starch or agar per litre — and produce a softer set than dairy.

Choosing a starter culture

Store-bought plain yogurt Use 2–3 tablespoons per litre. Must list live active cultures. Can be re-cultured 5–7 batches before the culture weakens.

Freeze-dried sachets One sachet (1–2 g) per 1–2 litres per brand instructions. More consistent strain counts than re-culturing from a tub.

Heirloom / reusable cultures Can be re-cultured indefinitely with proper care. Often include additional strains like L. acidophilus or Bifidobacterium.

More starter does not mean thicker yogurt. Overloading the milk (more than 3 tablespoons per litre) crowds the bacteria and causes grainy, overly sour results. Use the yogurt starter calculator to size the amount precisely.

How to make homemade yogurt, step by step

1
Heat the milk Warm milk to 82–85°C / 180–185°F in a heavy-bottomed pot. Hold for 5–10 minutes. This denatures the whey proteins for a thicker set.
2
Cool to culturing temperature Let the milk drop to 40–46°C / 105–115°F. The sweet spot is 43°C / 110°F. Above 50°C kills the cultures; below 37°C stalls fermentation.
3
Add the starter Stir in your yogurt culture — a few tablespoons of live yogurt or a measured sachet. Whisk gently so it disperses evenly through the milk.
4
Incubate Hold the mixture at 40–46°C for 6–12 hours. Shorter times (6–8 hours) yield milder yogurt; longer (10–12 hours) means tangier and thicker. Do not disturb or stir during incubation.
5
Refrigerate Once set, refrigerate immediately for at least 4–6 hours to stop fermentation and firm up the texture. The yogurt will thicken further as it chills.

Incubation methods that work at home

You need a way to hold the milk at a steady 40–46°C for several hours. Any of these methods work:

Oven with the light on holds roughly 32–46°C depending on the oven. Check with a thermometer first — some run too cool.

Instant Pot yogurt setting maintains ~43°C automatically. The most hands-off method.

Dedicated yogurt maker maintains a precise warm zone. Worth it if you make yogurt weekly.

Cooler or thermos with warm water fill a cooler with 46°C water, set the sealed jars inside. Holds temperature for hours.

Straining for Greek-style yogurt

To turn your homemade yogurt into Greek yogurt, strain it through a cheesecloth-lined sieve set over a bowl in the fridge. Strain for 1–2 hours for a thicker breakfast yogurt, 2–4 hours for classic Greek texture, or 6+ hours for a dense, spreadable labneh. Expect your yield to drop to about 40–50% of the starting volume.

Save the strained whey — it is protein-rich and works well in smoothies, baking, and soups. For a deeper walkthrough on straining, see the full Greek yogurt guide.

Troubleshooting common problems

Runny or thin Milk was not heated to 82°C, incubation was too cool, or the batch did not incubate long enough. Adding milk powder before heating also helps, especially with lower-fat milk.

Too sour Incubated too long or too warm, or too much starter was used. Pull the batch earlier next time — as soon as it holds its shape when tilted.

Grainy or lumpy Too much starter, temperature swings during incubation, or the milk was overheated. Use less starter and maintain a steadier temperature.

Whey separation on top A thin layer of whey is normal. Excessive separation means the batch incubated too long, was disturbed during incubation, or cooled too slowly. Stir the whey back in or strain it off.

Try the calculator

Yogurt Starter Calculator

Size the starter amount precisely so the set is consistent every time.

Open calculator →

Keep exploring cultured dairy

Once you have the basic method down, try the Greek yogurt guide for straining technique, the yogurt milk ratio calculator to scale batches, or the best yogurt maker guide if you want dedicated equipment. If you are curious about drinkable fermented dairy, kefir uses a completely different grain-based culture and ferments at room temperature.