Homemade Yogurt Culture Ratio Calculator
Calculate the correct amount of starter culture for homemade yogurt from any batch size, with fermentation time and temperature guide.
Yogurt Recipe
Making Yogurt at Home
Yogurt is made by fermenting warm milk with live bacterial cultures — primarily Lactobacillus bulgaricus and Streptococcus thermophilus. The ratio of starter to milk and the fermentation temperature are the two most critical variables.
Starter Culture Ratio
| Type | Ratio | Notes |
|---|---|---|
| Store-bought yogurt starter | 2–3 tbsp per liter | Must contain live cultures |
| Freeze-dried starter culture | 1 packet per 1–4 L | Follow packet instructions |
| Saved from previous batch | 2 tbsp per liter | Works up to 5–7 generations |
Too much starter can actually cause the yogurt to set too quickly and produce a grainy texture. Too little starter leads to under-fermentation — watery, sour yogurt.
Fermentation Temperature
The bacteria thrive in a specific temperature range. Outside this range, they either die or become dormant:
| Temperature | Effect |
|---|---|
| Below 30°C (86°F) | Too cold — bacteria go dormant, yogurt doesn’t set |
| 40–43°C (104–109°F) | Optimal — firm, tangy yogurt in 4–8 hours |
| Above 46°C (115°F) | Too hot — bacteria die, batch fails |
The Process
- Heat milk to 82°C (180°F) — denatures whey proteins for a thicker texture.
- Cool to 43°C (109°F) — use a thermometer, not guesswork.
- Whisk in the starter culture.
- Incubate at 40–43°C for 4–12 hours.
- Refrigerate — yogurt thickens further when cold.
Thickness Control
- Thicker yogurt: strain through cheesecloth for 30–60 minutes to make Greek-style yogurt.
- Even thicker: add 2 tbsp of powdered milk per liter before heating.
- Thinner: use lower-fat milk or shorter fermentation time.
Fermentation Time Guide
| Time at 43°C | Result |
|---|---|
| 4 hours | Mild, slightly tangy |
| 6–8 hours | Balanced, classic yogurt flavor |
| 10–12 hours | Very tangy, strong sour flavor |
Shorter incubation = milder flavor. Longer incubation = more tart and more probiotic activity.