Yeast turns sweet wort into beer. It consumes fermentable sugars and produces alcohol, carbon dioxide and many of the flavours that define your finished brew.

Pitch too little yeast and fermentation may start slowly, stall early or create unwanted flavours. Pitch the right amount and your beer is more likely to ferment cleanly, reach its expected final gravity and taste the way the recipe intended.

What does “pitching yeast” mean?

Pitching yeast simply means adding yeast to your cooled wort before fermentation begins.

The amount of yeast required depends on several factors:

• Batch volume
• Original gravity
• Beer style
• Fermentation temperature
• Whether you are brewing an ale or lager
• Yeast age and viability
• Whether you are using dry yeast, liquid yeast or a yeast starter

Why the right amount of yeast matters

A healthy fermentation starts with enough active yeast cells.

Underpitching can lead to:

• Slow fermentation
• Higher risk of stuck fermentation
• Excess fruity, solvent-like or buttery flavours
• Poor attenuation
• Lower alcohol than expected

Overpitching is less common for most home brewers, but very large yeast quantities can reduce ester character and make some styles taste less expressive.

For most standard homebrew kits and extract recipes, the yeast included is designed for a typical batch size. The main time you need to think more carefully about pitching rates is when brewing larger batches, high-alcohol beers, cold-fermented lagers or recipes with a high original gravity.

How much dry yeast do I need?

For many 20 to 23 litre ale batches with an original gravity around 1.040 to 1.055, one fresh sachet of quality dry brewing yeast is often enough.

However, you may need more yeast when:

• Your batch is larger than usual
• Your beer is stronger than around 5.5% ABV
• You are brewing a lager
• Your yeast is old or poorly stored
• You are fermenting at the cooler end of the yeast’s recommended range

Lagers generally need more yeast than ales because they ferment at lower temperatures and yeast reproduces more slowly in cooler conditions.

How much liquid yeast do I need?

Liquid yeast packs can be excellent for style-specific flavour, but yeast viability drops over time. A pack that is close to its best-before date may not contain enough healthy cells for a full batch.

For standard-strength ales, a fresh liquid yeast pack may be enough. For lagers, high-gravity beers or older packs, making a yeast starter is often the best option.

A starter gives yeast time to wake up and multiply before it goes into your main batch.

You can find all our Brewing Yeast

Use a yeast pitching calculator

The easiest way to work out your pitching rate is to use a calculator.

Enter your batch volume, original gravity, yeast type and beer style, then use the result as a practical guide for how much yeast you need.

Brewing Calculators

Dry yeast: rehydrate or sprinkle?

Many modern dry brewing yeasts can be sprinkled directly onto cooled wort, provided the wort is well aerated and within the recommended temperature range.

Rehydrating dry yeast in clean, sanitised water can help the cells recover before pitching, but always follow the yeast manufacturer’s instructions. Different yeast strains have different recommendations.

Do not rehydrate yeast in hot water, sugary wort or sanitiser solution.

Signs you may not have pitched enough yeast

A batch may be underpitched if you notice:

• No signs of fermentation after 24 to 36 hours
• Gravity dropping very slowly
• Fermentation stopping well above the expected final gravity
• Strong green apple, buttery or solvent-like flavours
• Excessively sweet beer after conditioning

Before adding more yeast, check your fermentation temperature and take a hydrometer reading. Airlock activity alone is not a reliable way to judge fermentation.

[Link: How to Take a Hydrometer Reading]

Best practice for pitching yeast

1. Check the yeast best-before date.
2. Store yeast correctly before use.
3. Cool wort to the yeast’s recommended fermentation temperature.
4. Oxygenate or aerate the wort before pitching.
5. Use enough yeast for the volume and gravity of your batch.
6. Maintain a stable fermentation temperature.
7. Confirm fermentation has finished with stable hydrometer readings.

Frequently asked questions

Can I use two yeast sachets in one batch?

Yes. This is often a sensible choice for strong beers, large batches and lagers. It is usually safer to pitch slightly more healthy yeast than too little.

Can I add more yeast after fermentation has started?

Yes, but first make sure fermentation has actually stalled. Check gravity, temperature and recipe expectations before adding more yeast.

Does higher alcohol beer need more yeast?

Usually, yes. Higher gravity wort places more stress on yeast, so stronger beers often benefit from a larger pitch or a properly prepared yeast starter.