Harvesting yeast from a bottle-conditioned commercial beer

Which beers carry live yeast

Bottle-conditioned beers are carbonated in the bottle by a small dose of yeast and sugar. Look for a thin layer of sediment at the bottom and words such as bottle conditioned, refermented in the bottle or contains live yeast on the label. Many traditional Belgian ales, some British ales and German wheat beers and a number of craft beers are made this way.

Two catches. Some breweries condition with a different yeast from the one used for main fermentation, so you may harvest the bottling strain rather than the house strain. Others filter and pasteurise, which kills the yeast. Most mainstream beers in India are filtered and pasteurised, so they will not work. Imported or craft bottle-conditioned beers are your best bet.

Choose the freshest bottle you can

Yeast in a bottle dies slowly over time. Heat kills it faster. A bottle that has spent months on a warm shop shelf may carry very few living cells. Check the bottling or best-before date and choose the freshest. Buy two or three bottles of the same beer if you can, which gives you more yeast and a second chance.

Store the bottles upright in the fridge for a few days before you harvest. The yeast settles into a firm layer and stays alive longer in the cold.

Pour the beer, keep the dregs

Sanitise the outside of the bottle neck and cap with sanitiser spray before opening. Open it and pour the beer carefully into a glass, leaving the last 1 to 2 cm and the sediment in the bottle. Enjoy the beer; it tells you what the yeast tastes like.

Spray the neck again and cover it with sanitised foil while you prepare the starter. Work quickly and keep everything clean. At this stage, you have a tiny number of yeast cells and any bacteria that get in can outgrow them.

Step one: a very small starter

The mistake most people make is pitching the dregs straight into a full litre of wort. A few cells in a big volume are overwhelmed. The starter is slow and prone to infection. Start small instead.

Make about 100 to 200 ml of weak wort at around 1.020 to 1.030 by boiling a spoonful or two of dry malt extract in water. Cool it to room temperature, swirl the dregs to loosen them and pour the wort into the bottle itself, or tip the dregs into a small sanitised jar of wort. Cover with sanitised foil. Keep it at about 20 to 24 °C and swirl it whenever you pass.

Activity can take two to five days to appear. You will see a fine layer of fresh yeast at the bottom and a few bubbles.

Step it up, about tenfold at a time

Once the small starter has fermented, step it up. Each step should be roughly ten times the volume of the last: 200 ml to about 2 litres is a common next step, at a normal starter gravity of around 1.035 to 1.040. Let each step ferment fully, which usually takes one to two days.

For a 20 litre batch of ordinary-strength beer, a 2 litre starter grown from a healthy culture usually gives a reasonable pitch. Our guide to pitching yeast properly explains how many cells you need and why underpitching causes trouble.

Smell and taste before you trust it

Before pitching, smell and taste the starter beer. It should smell like the beer you poured from the bottle, or simply bready and yeasty. Sour, vinegar, nail varnish or rotten smells mean contamination. The starter goes down the sink.

A careful brewer pours off the spent starter beer before pitching and pitches only the yeast layer, so off-flavours from the starter do not end up in the batch. If you want to keep the strain, save a small amount of the slurry in a sanitised jar in the fridge and step it up again for the next brew.

Why it is worth the effort

Harvesting from a bottle takes a week or more and does not always work. But it teaches you yeast handling better than any sachet: cell growth, starter gravity, sanitation and smell. It also lets you brew with strains that are hard to buy in India. Once you have harvested yeast, pour your own bottle-conditioned homebrew carefully; our guide to pouring without the yeast shows how.

Your first step: find a fresh bottle-conditioned beer with clear sediment and keep it upright in the fridge while you buy a bag of dry malt extract for the starter.

Common questions

Can I harvest yeast from any bottled beer?

Only from bottle-conditioned beers with live yeast in the sediment. Filtered and pasteurised beers, including most mainstream beers in India, carry no live yeast.

What gravity should the first starter be?

Keep the first step weak, about 1.020 to 1.030. Keep it small too, around 100 to 200 ml, so the few surviving cells are not stressed.

How long does it take to grow yeast from a bottle?

Usually a week or more across two or three steps. The first small step alone can take two to five days to show activity.

Is the harvested yeast the same as the brewery's main strain?

Not always. Some breweries bottle condition with a different yeast from the one used for main fermentation.