Do I need a starter for dry yeast?

Usually not. An 11g sachet of dry yeast contains roughly 230 billion cells, which is enough for most standard ales. Starters are more important for liquid yeast (100 billion cells) or high-gravity beers.

How does yeast age affect viability?

Liquid yeast viability drops about 21% per month from manufacture date. A pack 3 months old may only have about 50% viable cells. This is why starters are essential for liquid yeast — they grow fresh, active cells.

What is a step-up starter?

When you need more cells than a single starter can grow (typically over 4 litres), you do two steps. Grow the first starter, chill and decant the spent wort, then add fresh starter wort for a second growth phase.

What gravity should my starter be?

Target 1.036-1.040 (about 100g DME per litre). Higher gravities stress the yeast and reduce growth. The goal is cell multiplication, not fermentation.

How long should I run a starter on a stir plate?

Most starters reach peak growth in 24-36 hours on a stir plate. You can chill and decant after 24 hours, then pitch the slurry. Longer is not better — cells start dying after nutrients are depleted.

BrewCalcs

Yeast Starter Calculator — Starter Sizing

Calculate yeast starter volume and DME for healthy fermentation with viability and step-up support.

Target OG

Original gravity of your beer

Batch Volume

Volume measurement

Yeast TypeYeast strain or type

Yeast Age

Days since manufacture date

Number of Packs

Enter the number of packs

How We Calculate This

Pitch Rate Calculation

Ales need approximately 0.75 million cells per ml per degree Plato. Higher-gravity beers need proportionally more yeast. The calculator determines total cells needed, estimates current viability from pack age, and works out the starter size to bridge the gap.

Growth on a Stir Plate

A stir plate starter grows approximately 200 billion cells per litre of 1.037 starter wort. If more than 4 litres is needed, a step-up approach is recommended.

Frequently Asked Questions

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Yeast Propagation Calculator

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Last updated: February 2026

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.