Yeast Handling — Pitch, Share, Repitch

Yeast is the only living ingredient in beer, and treating it well is most of what separates a clean fermentation from a sluggish or off one. The good news is that modern dry yeast is robust, stable and simple to use well.

It is also the ingredient most worth co-ordinating on. A sachet costs more than the grain in a small beer, packs come in sizes that suit a 23 L batch rather than a 10 L one, and a healthy slurry is worth handing on rather than tipping out. Splitting and sharing is the easiest money the club saves — provided it is done cleanly, which is most of what the second half of this guide is about.

How much to pitch

The headline mistake is overpitching because a liquid-yeast calculator told you to. Those tools assume liquid yeast and overestimate dry yeast by 3–6×.

For dry yeast, weigh it: 0.5–1.0 g/L. For a typical 20–23 L ale that is 11–23 g — one or two standard 11 g sachets, not the 30–60 g a liquid calculator suggests. No cell counting needed; dry yeast viability is consistent and known.

Pitch rate still shapes flavour. Underpitching stresses the yeast — more esters, more fusels, a slow start, and a longer window in which diacetyl precursor accumulates. Heavy overpitching gives a faster, cleaner, less expressive ferment. For most ales, one well-stored sachet at the right temperature is the no-drama default.

Sprinkle or rehydrate?

For modern Lallemand and Fermentis strains, sprinkling dry onto the wort is the preferred method and performs as well as rehydration for most beers.

1. Sanitise the scissors and the top of the pack
2. Sprinkle evenly over the wort surface as the fermenter fills
3. The motion of filling mixes it in. Do not stir, and do not submerge the sachet

Rehydrate instead when the wort is stressful:

• High gravity above ~1.065 — more osmotic stress
• Soured or low-pH wort — rehydration buffers the shock

To rehydrate: sprinkle onto 10× its weight of clean 30–35 °C water (11 g → 110 mL), leave 15 minutes undisturbed, stir gently, then step the temperature down toward the wort so the slurry is within 10 °C before pitching. Never use distilled or RO water, and never let it cool slowly on its own — both cost viability.

Oxygen — the biggest single lever on off-flavours

Yeast needs dissolved oxygen to build the sterols and unsaturated fatty acids that make healthy cell membranes. It does this before fermentation proper starts, and it only gets one chance — once fermentation is underway, adding oxygen does harm rather than good.

Get this wrong and you get stressed yeast, which is the root of fusel alcohols, excess esters, a long lag phase, incomplete attenuation, and a longer window for diacetyl precursor to build up. If you are going to put effort into one thing to clean up your beer, put it here.

The one thing that catches people out is that dry yeast is the exception:

• First pitch of fresh dry yeast — splashing at transfer is enough. Dry yeast is propagated under high oxygen and comes packed with the reserves it needs, which is why the manufacturers state it does not require oxygenating. Extra effort here is not wrong, just unnecessary
• Repitched slurry — aerate properly, to 8–10 ppm dissolved oxygen. Harvested yeast has spent its reserves and has to rebuild them
• Liquid yeast — aerate properly. It was never packed with reserves the way dry yeast is
• High-gravity wort above ~1.065 — aerate, even on a fresh dry pitch, or pitch more. The osmotic stress is on top of everything else

How to aerate, in rough order of effectiveness: pure oxygen through a sanitised diffusion stone (30–60 seconds), an aquarium pump and stone with an inline air filter (20–30 minutes), or vigorous shaking or stirring of a sealed fermenter for several minutes. All of it happens on chilled wort, before pitching — aerating hot wort oxidises it instead.

Nutrition — when it stops being optional

Yeast needs more than sugar. Two things are worth knowing by name.

FAN (free amino nitrogen) is the pool of yeast-usable nitrogen in your wort, and the yeast builds its amino acids from it. Run short and the yeast makes its own — which is precisely how you get diacetyl (a by-product of the valine pathway) and sulfur (rotten-egg H₂S from the sulfate reduction pathway backing up). Most of your FAN is set in the mash, not the fermenter, and you cannot nutrient your way out of a fundamentally lean wort — you can only compensate.

Zinc is the one trace mineral homebrewers reliably run short of. It is a cofactor for alcohol dehydrogenase, the enzyme that finishes converting acetaldehyde into ethanol. Short of zinc, acetaldehyde lingers — the green-apple, solvent, fresh-cut-pumpkin character in a young beer. Brewing salts do not supply it; a yeast nutrient blend does.

When nutrient goes from nice-to-have to necessary:

On an ordinary all-malt ale at normal gravity with a fresh pitch, wort nutrient is a small insurance policy. On any of the rows above, it is doing real work.

Storing packs

Keep a spare sachet in the fridge as a stuck-fermentation rescue. Dry yeast’s shelf stability means you can have backup on hand without planning ahead — and it means the club can hold a couple of workhorse strains between brew days without waste.

Splitting a pack between members

An 11 g sachet is more than a small batch needs, and splitting one is straightforward as long as you treat the open pack as a deadline rather than a stored ingredient.

• Split it dry, at the point of use, on a sanitised surface with a sanitised blade and a 0.1 g scale. Do not open a pack “to divide later”
• Vacuum-reseal any remainder immediately, and get it below 4 °C. Resealed, it is good to the printed expiry; not resealed, it is a three-day ingredient
• Split by weight, not by eye. Half a sachet by volume is not half a sachet by cell count
• Label it — strain and date. An unlabelled bag of beige powder in a shared fridge is a future mystery fermentation

The same logic covers a group buy: buying a box of one strain is much cheaper per batch than individual sachets, but only if the packs stay sealed until someone is actually brewing.

Harvesting and repitching

Repitching cuts cost per brew sharply, and dry yeast is a good base for it because generation one is a known, clean starting point. Worth doing for a strain you brew regularly, not for one-offs.

Harvest the healthy fraction:

• Promote flocculation with adequate calcium (50–150 ppm) in the mash
• On a conical, dump the first dark slurry — early flocculators and trub — then harvest the creamy, light-brown middle of the cone within ~24 h of reaching terminal gravity. Avoid the top, which is slow and mutated cells
• On a flat-bottomed fermenter, take from the middle of the bed after the trub has settled and accept that it will be less clean

Store it: chill rapidly to 4 °C in a sanitised vessel with minimal air, and use within about a week.

Repitch it: aerate the wort, add yeast nutrient (the benefit grows from about generation 4), and keep simple records — strain, generation, source batch, how it fermented.

Passing a slurry to another member

A slurry is a genuinely useful thing to hand on, and also a genuinely good way to hand someone a problem. Three rules:

1. Say what it came off. Strain, generation, the beer it fermented, and its IBU and ABV. The person receiving it needs all four to know whether it is worth pitching
2. Fresh or not at all. A week at 4 °C is the working limit. Do not pass on something that has been sitting since your last brew day
3. Sanitised, sealed, labelled. A jar that has been open on a bench is not a gift

If you have brewed anything wild or sour, none of your fermenting kit or yeast goes to anyone else — see Cleaning & Sanitation.

Never repitch from these

• Any sour or mixed-culture beer — never
• High gravity above 8% ABV
• Heavily hopped above ~60 IBU, or heavily dry-hopped — hop compounds degrade yeast vitality
• Anything that showed a fault. Passing on a slurry from a batch that had a phenolic or diastatic problem spreads it. See Bandaid, TCP & Clove

After several generations, bacteria and wild yeast slowly accumulate. Refresh from a new pack periodically rather than chasing a strain forever.

Quick reference

See also: the yeast pages for each strain’s attenuation range, temperature band and flocculation, and Reading Gravity for checking your fermentation against them.