Same lesson, with the figures in motion.
Yeast Washing 101
Why wash the yeast?
Washing separates the yeast from the rest and leaves you with clean, pale slurry in a bottle that keeps for a few weeks in the fridge. Allow an hour at the bench plus a night in the fridge — and expect a single cake to cover several brews.
1. Prep & Dilute
Pour your pre-boiled, cooled water straight into the fermenter, right on top of the dirty yeast cake. Five litres in a 20-litre (5 US gal) bucket is plenty — you need air left to shake in.
Harvest from a cake that has stood for a few days, not a few weeks. Yeast that has sat a long time on its own trub gets stressed, starts sluggishly and can give rubbery off-flavours next time.
2. Shake It Loose
Put the lid back on the fermenter and shake hard! Break the yeast cake apart completely until the water looks like a thick, muddy soup.
Everything is in suspension now, all mixed together — yeast, trub and hop debris. That is exactly the state the next step builds on.
3. Fill the Jars
Now the first new vessel enters the picture — and this is where the yeast will live. Sanitise the glass jars and their lids with Star San, then pour over part of the slurry. Do not fill them to the brim; there should be air left under the lid.
Why not let it settle in the bucket? Because a bucket is wide and opaque. In a tall glass jar the layers are easy to see, the jar fits in the fridge, and you can decant without stirring up the bottom. None of that works in the bucket.
4. Let Gravity Work
Let the jars stand completely still for 20–30 minutes. The heavy, dark trub sinks quickly to the bottom, while the lighter yeast stays up in the milky liquid above.
Do not wait too long. Leave the jar for a few hours and the yeast will have settled on top of the trub — and then there is nothing left to pour off.
How well it works depends on the strain. A low-flocculating yeast stays up nicely; a high-flocculating one clumps together and goes down with the trub. Flocculation is listed for every strain in the yeast library.
5. Harvest the Yeast
Carefully pour the milky liquid into a smaller vessel you have sanitised with Star San — a glass bottle or a small jar. Stop pouring the second you see the dark trub from the bottom trying to follow along.
Better slightly too little than slightly too much. What you leave behind is trub; what you take with you is yeast.
6. Crash & Pitch
Put the vessel in the fridge. Over a few days the yeast packs into a clean, white layer at the bottom. On brew day you decant the water, let the vessel come to room temperature and measure your slurry into our Pitch Calculator!
Use the harvest within a couple of weeks. Viability drops with every day in the fridge, and that is exactly the number the calculator asks for — an old harvest needs more volume for the same cell count.
Want to practise pouring off at the right moment – in the game Layers?
Play →