Greek Yogurt: How It Works and How to Make It at Home

You warm milk, add a live yogurt culture, and hold it in a narrow warm zone while the bacteria ferment lactose into lactic acid. That acid thickens the milk and gives yogurt its tang. Then you strain — and because Greek yogurt is just strained yogurt, a good batch depends first on a good base set.

If you nail the starter amount, temperature, and incubation time, straining simply concentrates an already-good yogurt. Get the base wrong and no amount of straining will rescue it. Size your culture with the yogurt starter calculator and sanity-check the proportions with the yogurt milk ratio calculator before you heat anything.

Greek yogurt is made by straining, and straining is what concentrates it. Per 100 g, USDA FoodData Central lists plain whole milk Greek yogurt at about 2.5 times the protein of plain whole milk yogurt:

Figures from USDA FoodData Central records 171284 and 171304. Brands differ, so check the label you are buying.

Not every thick yogurt on the shelf is strained. Some are thickened by adding milk protein, starch, gelatine or pectin instead of draining whey. Read the ingredients: a strained yogurt lists little more than milk and cultures.

In the UK, the name is protected. The Court of Appeal ruled in 2014 that “Greek yoghurt” means yoghurt strained to remove the whey, made in Greece and without additives (Fage UK v Chobani UK [2014] EWCA Civ 5). Thick yoghurt made elsewhere is sold as “Greek-style”. In the US, “Greek” describes the style, not where it was made. Strained at home, yours is Greek-style in UK terms and Greek yogurt in US terms; the method is the same.

1. 1
   Heat the milk Warm milk to about 82°C / 180°F to denature the proteins, which helps build a firmer set. Hold it briefly, then cool.
2. 2
   Cool to culturing temperature Let the milk drop to roughly 43°C / 110°F — warm to the touch but not hot. Too hot will kill the culture.
3. 3
   Add the starter Stir in your yogurt culture (a few tablespoons of live plain yogurt, or a measured sachet). Whisk gently so it disperses evenly.
4. 4
   Incubate Hold the mixture at 40–45°C / 104–113°F for 6–12 hours until it sets. Longer incubation means a tangier, firmer base.
5. 5
   Chill fully Refrigerate the set yogurt for several hours. Straining warm yogurt removes your control over the final texture, so chill first.
6. 6
   Strain Line a sieve with a clean cloth or coffee filter, set it over a bowl, and let the whey drip away in the fridge until the yogurt reaches the thickness you want.

Straining is a concentration step, so your final Greek yogurt weighs noticeably less than the milk you started with. As a rough rule, plan on 400–500g of Greek yogurt per litre of milk. The longer you strain, the more whey leaves and the lower — but thicker — your yield becomes. To get the exact figure for your batch, use the Greek yogurt yield calculator — set your milk volume, fat, and straining time to see the strained yield and leftover whey.

This is the same volume-to-yield logic that drives cheese making. If you want to model that relationship more precisely for planning batches, the cheese yield calculator and the milk-to-cheese calculator are useful analogues — the idea of “how much liquid leaves and how much solid stays” is identical.

Strain in the refrigerator, never at room temperature — cold straining keeps the bacteria from over-souring the batch and avoids food-safety risk over a long drip.

Save the strained whey — it’s protein-rich and works well in smoothies, baking, and soups.

Greek yogurt is one branch of a much bigger cultured-dairy family. Start at the yogurt hub for starter sizing and milk-ratio tools, try kefir if you want a thinner, drinkable ferment with its own grain-based culture, or move into cheese when you’re ready to take straining and concentration all the way. If you like your yogurt cold, see our guide on frozen yogurt, and if you are ready to buy equipment, check our best yogurt maker picks.