Yogurt Starter Culture Ratio Calculator
Measure the right amount of yogurt starter for your batch of milk — too little is slow, too much crowds the culture and thins the set.
How it works
starter (ml) = milk (litres) × rate · rate = 15 / 22.5 / 30 ml per litre for mild / balanced / tangy
Yogurt is milk fermented by live bacteria, and the starter simply seeds those bacteria — you need only a small, active dose. Counterintuitively, more starter does not make a firmer set: overcrowding the culture makes the bacteria compete, ferment fast and produce a thinner, grainier, more sour yogurt. About one to two tablespoons of live plain yogurt per litre of milk is plenty. The two things that decide success are a healthy starter and holding the milk near 43°C (110°F) for several hours — hotter kills the culture, cooler stalls it.
Worked example
To culture 1 litre of milk for a balanced tang, stir in about 22 ml — roughly 1½ tablespoons — of live plain yogurt once the milk has cooled to 43°C. Hold it undisturbed in a warm spot for 4 to 8 hours: shorter for mild and looser, longer for tangier and firmer, then refrigerate to stop it.
Frequently asked questions
Can I use store-bought yogurt as starter?
Yes, as long as the label says live or active cultures and it is plain and unsweetened. Sweeteners, thickeners and heat-treated yogurts make an unreliable starter.
Why did my yogurt come out runny?
Common causes are too much starter, incubation that was too cool or too short, or an old/weak culture. Heating the milk to about 82°C (180°F) first and cooling it back to 43°C also thickens the set by denaturing the proteins.
How many times can I reuse my own yogurt as starter?
Usually several batches, but the culture gradually weakens and can pick up stray microbes. If sets slow down or the flavor drifts, start fresh from a new live yogurt.
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This calculator is for educational purposes. Double-check important results before acting on them.