Yeast Starter Calculator

Plan a yeast starter: the cells you need, the viable cells in your yeast and how many a still, shaken or stir-plate starter grows, in up to three steps.

A starter grows new yeast roughly in proportion to the sugar it holds: about 1.3 to 1.7 billion cells per gram of extract in one published experiment. A 1 L stir-plate starter at 1.036 grows about 159 billion cells, enough to take a 30-day-old liquid yeast pack from 89 to about 247 billion.

Reviewed by Diego Santiago, Professional Brewer

MetricUSImperial (UK)

1. Cells you need

Pitch rate (M cells/mL/°P)

About 0.75 for ales and 1.5 for lagers

Batch volume (L)

Volume of wort you pitch into

Wort gravity (SG)

Original gravity of the beer

2. Yeast you have

Yeast type

Amount (mL)

At 1 billion cells per mL when fresh

Manufacture date

Printed on the package; fills in the days below

Days since manufacture (days)

3. Starter steps

Step 1

StillShakenStir plate

Starter volume (L)

Starter gravity (SG)

Often 1.030 to 1.040

Growth (billion cells/g)

Per gram of extract; see the notes below

Grows about 317 billion cells, to 406 billion. Make it with about 205.4 g of dry malt extract.

Cells needed179billionCells after the starter406billionEnough yeastYes

Results are estimates provided "as is," for informational and planning purposes only, without warranties of any kind. Check them before you rely on them: you are responsible for decisions about your beer and equipment, including pressure and carbonation levels, the pressure ratings of your kegs and fittings, and any alcohol content you declare. Use of this calculator is subject to our Terms and Conditions.

Plan recipes, track every batch and keep all your brewing numbers in one place. Foambyte is free to start.

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How the starter is calculated

First the calculator works out the cells your beer needs from the pitch rate, the batch volume and its gravity, and the viable cells in your yeast from its type, amount and age, the same as the pitch rate and yeast viability calculators.

Each starter step then adds yeast in proportion to the extract in the starter wort:

N_{after} = N_{pitched} + E \times Y

where $N$ is billions of cells, $Y$ the growth in billion cells per gram of extract, and $E$ the grams of extract in the starter:

E = V \times SG \times 0.998 \times 10 \times \text{°P}

with $V$ in liters. The default growth figures, about 1.4 billion cells per gram for a still starter, 1.3 for a shaken one and 1.7 on a stir plate, come from an experiment by Kai Troester. Each step starts from the cells at the end of the one before.

For example, a 20 L ale at 1.048 pitched at 0.75 million cells per mL per °P needs about 179 billion cells. A 30-day-old 100-billion-cell pack of liquid yeast has about 89 billion viable cells. A 1 L stir-plate starter at 1.036, made with about 103 g of dry malt extract, holds 93 g of extract and grows about 159 billion cells, for about 247 billion: enough for the batch.

Inside Foambyte, the pitch rate and yeast starter calculator in the app’s tools checks the viable cells in your yeast against your recipe before brew day.

Reference table

Billion cells grown on a stir plate (1.7 billion per gram of extract) by starter volume (rows) and gravity (columns), not counting the cells pitched
Starter \ gravity	1.030	1.036	1.040
0.5 L (0.13 gal)	66	79	88
1.0 L (0.26 gal)	132	159	176
1.5 L (0.40 gal)	198	238	265
2.0 L (0.53 gal)	264	317	353
3.0 L (0.79 gal)	396	476	529
4.0 L (1.06 gal)	528	635	705

Sources

Kai Troester. “Yeast propagation experiment”, Braukaiser, 2012. Yeast grown per gram of starter extract (about 1.4 billion still, 1.3 shaken and 1.7 stirred), estimated from yeast weight in 12 °P wort; archived copy, as the original site is not reachable.

Frequently asked questions

How does a starter grow yeast?

The yeast you pitch ferments the starter wort and multiplies while it does. In this calculator the new cells are proportional to the extract (dissolved sugar) in the starter, so a bigger or stronger starter grows more yeast.

How accurate is the growth estimate?

It is a rough planning number. The growth figures come from a single published experiment that estimated cells from the weight of the yeast grown, and other brewers have reported much larger gains from stir plates. Very small or very large pitches into a starter, oxygen, nutrients and temperature all change the result. Adjust the growth figure if you count your own cells.

Why use a stir plate?

Stirring keeps the yeast in suspension and lets CO₂ escape and oxygen in, which generally helps growth. In the experiment behind the default figures, the stirred starter grew more yeast per gram of extract than the still and shaken ones.

What gravity should a starter have?

Many brewers make starters at about 1.030 to 1.040. Stronger wort stresses the yeast, and the beer from a starter is usually poured off before pitching.

When do I need a starter?

When the viable cells in your yeast are fewer than the cells your beer needs, which is common for lagers, stronger beers and older yeast. The pitch rate calculator shows the cells needed on its own.