Yeast Starter Calculator

How it works

Starter wort ≈ 100 g DME per litre (SG 1.037); new cells ≈ growth (billion per g of extract, 0.4–1.4 by inoculation rate) × grams of extract, reduced 15% for shaking and 30% for still starters

A starter is a small fermentation whose only purpose is to multiply cells. Yeast grows most when it is pitched thinly into fresh wort, so a given pack yields more cells in two litres than in one, but with diminishing returns — the growth models (this one follows Braukaiser’s stir-plate data) give more than a billion new cells per gram of extract at low inoculation rates and under half a billion when the wort is crowded. Constant stirring keeps yeast suspended and oxygenated and roughly doubles growth compared with a starter left still. Starter wort at about 1.037 (100 g of DME per litre) balances growth against stress. When one step cannot reach the target, chill, decant and step up into a second, larger starter.

Worked example

From 57 billion viable cells toward 207 billion on a stir plate: a 2 L starter (200 g DME) grows to about 320 billion — enough with margin.

Frequently asked questions