How to make yogurt at home: temperature, timing and troubleshooting

Yogurt is milk acidified and coagulated by two bacteria: Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Both the Codex Alimentarius standard for fermented milks (CXS 243-2003) and Türkiye's Food Codex Regulation on Fermented Milk Products (2022/44) define yogurt as exactly this pair of cultures used together.

Both bacteria like heat, but their optima are not identical, so success at home comes down to holding the overlap band of 42-45 °C (108-113 °F). The steps below rest on the temperatures, times and pH values measured in university-based home food preparation guides.

This is a technical kitchen guide; it makes no health claims and offers no health advice.

1. Clean the containers and tools Wash the pan, jar, lid, spoon and thermometer in hot detergent water, rinse well and let them air dry. The shelf life of your yogurt depends directly on this: moulds and yeasts that get in will spoil it within days. Do not towel-dry with a cloth or a used sponge, as both carry microorganisms. Skipping this step wastes all the temperature precision that follows.
2. Choose your milk, and pasteurize it first if it is raw Pasteurized and UHT milk from the shop has already been heat treated and can be used directly. Türkiye's Ministry of Agriculture and Forestry consumer bulletin defines pasteurization as 63 °C (145 °F) for 30 minutes or 72 °C (162 °F) for 15 seconds, and UHT as no less than 135 °C (275 °F), and advises against consuming raw milk. If you are using hand-milked or unpackaged milk, pasteurize it before making yogurt: bring it to 74 °C (165 °F) while stirring constantly, then chill it rapidly in ice water. Acidity alone is not a sufficient barrier, since some pathogens such as E. coli O157:H7 are acid tolerant; safety comes from heat and acidity together.
3. Heat the milk to 85-93 °C (185-200 °F) and hold it 10-20 minutes Heat the milk gently in a heavy pan or double boiler, stirring, and bring it into the 85-93 °C (185-200 °F) band. Hold it there for 10 minutes for a thinner yogurt, or up to 20 minutes for a thicker one. This step does not replace pasteurization; its purpose is to alter the milk proteins so the gel sets as one body instead of breaking into curds and whey. Do not boil, as boiled milk tastes off and scorches on the bottom. If you are adding milk powder, stir it into cold milk — powder added to hot milk forms stringy clumps.
4. Cool the milk to 44-46 °C (112-115 °F) Set the pan in cold water to bring the temperature down fast, and confirm 44-46 °C (112-115 °F) with the thermometer. Adding starter to milk hotter than 46 °C (115 °F) kills the bacteria and the yogurt will never set. Impatience is the most common failure here: inoculating straight off the stove is the same as dropping the culture into boiling water. Dipping a finger in to judge warmth is not reliable — a guess by hand can easily be off by several degrees, and that gap is the difference between a set and a failed batch.
5. Add the starter, measured For 1 litre of milk, 2-3 tablespoons (about 50-60 ml) of plain live-culture yogurt is enough. Instead of dropping it straight into the pan, whisk it smooth with a cup of the warm milk, then stir that gently through the rest so the culture spreads evenly. The final mixture should sit around 43-44 °C (110-112 °F). More starter does not speed things up; it gives a grainy texture and excess sourness. The yogurt you use as starter must state live cultures on the label — heat-treated products, or ones thickened with starch or gelatin, will not work.
6. Incubate at 42-45 °C (108-113 °F) for 4-7 hours, undisturbed Fill the containers, cover them and place them somewhere that holds heat: a yogurt maker, an oven with only the light on, jars wrapped in a blanket, or a foam cooler holding 43 °C (110 °F) water. Aim for 42-45 °C (108-113 °F), the band where both bacteria work together: strain measurements published in the Journal of Dairy Science put the optimum growth temperature of S. thermophilus at 35-42 °C (95-108 °F) and that of L. bulgaricus at 43-46 °C (109-115 °F). Do not move, shake or stir the containers during this time — disturbing a gel that is still setting is the main cause of whey separation.
7. Check the set: the gel forms at pH 4.6 After the fourth hour, tilt the container gently; if the yogurt slides as one mass and holds a spoon mark, it is done. Milk proteins coagulate once the pH falls to 4.6; in the test kitchen of the national home food preservation centre the pH read 4.7 at about four hours, 4.6 at about five and 4.5 at about six, with a firm set at six hours. A lower incubation temperature simply means a longer wait. Do not stir it to check — a gel that has been broken will not knit back together.
8. Refrigerate immediately and keep it below 4 °C (40 °F) The moment the gel is firm, move the containers to the fridge: rapid cooling stops acid development, and every extra hour makes the yogurt sourer and eventually makes it weep. Homemade yogurt keeps for roughly 10-21 days held below 4 °C (40 °F); Türkiye's Food Codex likewise requires fermented milk products to be stored below 6 °C (43 °F). Discard the whole batch if you see mould, colour change, or any odour other than clean acidity. Set aside 2-3 spoonfuls as the starter for your next batch.

⚠ This guide is general information. Yudum cannot be held responsible for the outcome of following it; for official procedures always rely on the institution's own statement. Steps and fees change over time.

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