Cone harvesting yeast from a cylindroconical tank

The cone sorts the slurry into layers

As fermentation ends and the tank cools, everything heavy settles into the cone. It does not settle evenly. The first layer to land is trub and dead cells: dark, grainy and often bitter with hop matter. Above that sits the bulk of healthy yeast, thick and creamy. On top is a looser layer of late settling cells, which may be less flocculent or less active.

Good cone harvesting means dumping the bottom, taking the middle and leaving the top in the tank.

Timing the harvest

Most breweries harvest after the diacetyl rest and once the tank has been cooled, when the yeast has settled. Harvest too early and you take active yeast still needed to finish the beer. Leave it too long and yeast sit warm and compacted in the cone under pressure, where they start to break down.

The cone is often warmer than the beer above it, especially if the cone has its own jacket or no jacket at all. Yeast left there for days lose viability. A common practice is to harvest within a day or two of cooling. Our guide to the yeast growth phases explains why yeast at the end of fermentation are vulnerable.

Dump the trub first

Open the bottom valve slowly and run the first slurry to drain. It is usually darker, thinner and grittier than what follows. Watch it in a clear hose or a sight glass. When it changes to a pale, creamy, even slurry, start collecting.

The volume of trub depends on the brew. A beer with heavy whirlpool hops may have a lot. A clean lager with good separation may have little. Measure the dump volume and note it on the batch record so you can compare brews.

Collect the middle

Collect into a sanitised, carbon dioxide purged vessel or brink. Keep the flow slow. Tank pressure pushes the slurry out. The dissolved carbon dioxide comes out of solution as it does, so slurry foams in the receiving vessel.

Stop when the slurry becomes thin and runny, or when beer starts to come through. That top layer stays in the tank or goes to drain. Many brewers take only the middle third of the yeast crop to repitch.

How much do you need? Work it out before you open the valve. Our guide to pitch rate per degree Plato turns a target rate into litres of slurry. Harvesting a little more than the next pitch needs gives you room to discard anything doubtful. Harvesting three times as much only fills the brink with yeast that will be too old by the time you use it.

Pressure and safety

A fermenter at the end of fermentation can hold one bar or more of top pressure. Opening a cone valve under pressure can spray slurry with real force. Use a proper harvest hose with fittings rated for the pressure, open valves slowly and wear eye protection. Never stand directly in line with a valve as you open it.

Some breweries reduce top pressure before harvesting to make the slurry easier to handle. Reducing it too far lets gas come out of the beer, which brings foam and lifts the yeast. Find the setting that works on your tanks and write it down.

Look, smell and count

Healthy slurry is pale cream to light tan, thick but pourable and smells clean and yeasty. Dark slurry, grey streaks, a sulphury or meaty smell or a sour note are warning signs. Count and stain a sample for viability before you repitch. Our guide to yeast viability and vitality covers the method.

Store the crop cold straight away. Our guide to storing harvested yeast in a brink covers temperature and storage time.

Which tanks to harvest from

Harvest from healthy, typical fermentations of moderate strength. Yeast from a strong beer is stressed. Yeast from a fermentation that ran slow or hot may carry problems forward. Many breweries harvest from beers under about 7% ABV and avoid tanks that showed any sign of infection or odd flavour.

The beer you crop from also sets the oxygen and nutrient needs of the next batch. Our guide to wort aeration and oxygen covers how to match oxygen to the yeast you pitch.

Your first step this week

On your next harvest, run the dump into clear jugs one after another. Line them up and photograph the change from trub to yeast to thin slurry. That picture shows your team exactly where to start and stop collecting on your tanks.

Common questions

When should yeast be harvested from a fermenter?

Usually after the diacetyl rest and cooling, once the yeast has settled. Many breweries harvest within a day or two of cooling.

Which part of the cone yeast should I keep?

The creamy middle layer. Dump the dark trub at the bottom and leave the thin top layer behind.

Is harvesting yeast under pressure safe?

It can be, with rated fittings, slow valve opening and eye protection. Never stand in line with a valve as you open it.