Harvest at mid‑fermentation, hold your slurry cold in a sanitary brink, acid wash when needed, then pitch by the numbers. That recipe can cut yeast cost from ~$50 to ~$2 per barrel and keep fermentations consistent (blog.whitelabs.com).
Commercial breweries are turning a routine chore into a competitive advantage: harvest “clean” yeast at the same point every time, store it in a hygienic brink at 2–4 °C, run a quick acid wash when contamination creeps in, and pitch at a verified cell count and viability. The result is steadier fermentations, fewer off‑flavors, and material savings, with documented reuse across 5–10 generations (wyeastlab.com).
There’s a catch: consistency. The most important concept, according to one technical guide, is harvesting at the same fermentation point, temperature, and pressure to minimize variability (wyeastlab.com).
Mid‑fermentation yeast harvesting
Best practice is to harvest fresh yeast as fermentation nears the midpoint (≥50% attenuation; attenuation = degree of sugar consumption), when cells are healthiest and not yet stressed or exhausted (wyeastlab.com; blog.whitelabs.com). Brewers commonly vent CO₂ pressure (~3–5 psi) to aid harvest, then open the bottom conical valve to dump the “dirt” (the first and last skim of trub) and collect the middle, dense yeast slurry (wyeastlab.com; blog.whitelabs.com).
A typical schedule calls for skimming 24–36 hours into fermentation, discarding the first and last skims, and harvesting only the middle “clean” yeast. That consistency helps avoid both underpitching and selective mutation (where highly flocculant or attenuative strains dominate) (wyeastlab.com; wyeastlab.com).
Generations and performance tracking
Managed carefully, yeast can be repitched 5–10 times in commercial settings (wyeastlab.com). Cost savings are significant; one estimate pegs repitching as a way to reduce yeast cost from ~$50/barrel (single‑use) to ~$2/barrel (blog.whitelabs.com).
There are trade‑offs. Successive generations may slow fermentations: one trial found 4% ABV reached in 65, 94 and 100 hours on the 1st, 2nd, and 3rd pitches (annalsmicrobiology.biomedcentral.com). Over time, yeast can accumulate stress or minor mutations (annalsmicrobiology.biomedcentral.com; wyeastlab.com). Breweries monitor attenuation, fermentation time, and flavor as repitches accumulate.
Sanitary yeast brink design
Harvested yeast is stored in a dedicated “yeast brink” (a hygienic storage vessel) built like a mini‑fermenter: stainless‑steel, pressure‑rated, smooth, crevice‑free welds, and full CIP/SIP capability (CIP = clean‑in‑place; SIP = steam‑in‑place) (skeequipment.com; sp.paulmueller.com).
Typical specifications include 304 or 316L stainless steel with polished interior (#4 or better) to prevent microbial harborage; ASME‑rated construction with dish or cone bottom and fully welded seams; interior spray‑ball or rotary devices for CIP and the ability to steam‑sterilize (SIP); Tri‑clamp or sanitary‑flange inlets/outlets (e.g., 4–5” ports) for hose hookup; separate vents or CO₂ inlet with pressure gauge to purge oxygen; a sample valve; and a pressure/vacuum relief valve (sp.paulmueller.com; skeequipment.com).
Brinks often add glycol cooling to hold 2–4 °C, plus pressure/temperature gauges, optional tank lights or load cells for weight monitoring, and optional aseptic stirring or manual mixing to keep the slurry homogeneous (sp.paulmueller.com). For allied sanitary components in food‑grade service, 316L stainless steel housings are standard practice (ss‑cartridge‑housing).
Brink operation and sanitation practices
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After each batch, the brink is cleaned and sanitized; brewers typically spray the interior with sanitizer, flush, and dry before reuse. A continuous CO₂ headspace or mild positive pressure is maintained to exclude air. A practical note from operators: accumulate only as much yeast as needed, and decant the first liter of slurry after harvest because those heavier flocs tend to be the least vital (skeequipment.com).
Modern brinks range from 20–50 L units for microbreweries up to several hundred liters; working pressure ratings are typically 15–30 psi, which is well above fermentation pressure. Proper design virtually eliminates oxygen ingress and contamination—functionally a dedicated, pressurized SS tank with CIP, sampling, cooling, and instrumentation (skeequipment.com; sp.paulmueller.com).
Acid washing to suppress bacteria
To reduce bacterial contaminants in reused yeast, breweries employ a controlled “acid wash”: add food‑grade acid under cool, agitated conditions to drop pH to very low levels that kill bacteria while minimally harming yeast (wyeastlab.com; www.morebeer.com).
Common practice (Fal Allen, Pike Place Brewery) is to mix 75% phosphoric acid 1:9 with water (~7.5% solution), add slowly to the slurry with stirring, and monitor pH. Typical targets are pH 2.0–2.4 (occasionally 2.5 for gentler conditions) held for about 1–2 hours at 2–4 °C (wyeastlab.com; www.morebeer.com). As a working example, adding ~0.25–0.5 cup of the 7.5% solution to 4 gal (15 L) of yeast can reach pH ~2.0–2.4 (www.morebeer.com). Gentle agitation ensures uniform acid distribution; after a 1–1.5 h hold, the acid is typically neutralized or pitched as‑is (www.morebeer.com). For controlled addition, accurate chemical dosing is emphasized (dosing‑pump).
Key parameters: 75% food‑grade H₃PO₄ or chlorine dioxide (ClO₂) are used to lower pH to ~2.1–2.5 at 2–4 °C for 1–2 h; dosage is adjusted to hit that pH, checked by pH paper or meter frequently (wyeastlab.com). Weaker washes (pH ~2.5–3.0 for 6–12 h) can reduce stress on yeast, but are less bactericidal (www.morebeer.com).
Limitations matter: wild yeasts are not killed by acid washing—only bacteria are suppressed—and phosphoric acid reduces but does not guarantee elimination of bacteria; repeated washes may only lower bacterial load, not sterilize the culture (www.morebeer.com; wyeastlab.com; www.morebeer.com). Strain variability exists; repeated washes can stress yeast and reduce long‑term viability, so many breweries use acid wash as preventative maintenance (e.g., every 6–8 repitches) or when minor contamination is observed (www.morebeer.com; www.morebeer.com). If bacterial infection is severe, the safest practice is discarding the slurry and sourcing fresh culture (www.morebeer.com).
Viability staining and cell counts
Accurate pitching depends on the concentration of viable yeast cells. Breweries run rapid viability staining and microscopic counts on each harvest so pitch volumes can be calculated batch‑by‑batch. In the standard methylene blue test (0.5–1% aqueous), live cells remain colorless (enzymatically reducing the dye) while dead cells turn blue (www.brewiki.org; microbebrewer.blogspot.com). Prepare a well‑mixed slurry diluted 10–100×, add stain, wait ~1–5 minutes, then load into a hemocytometer (a calibrated counting chamber) and count by phase or bright‑field microscopy; viability (%) = (unstained/total)×100% (microbebrewer.blogspot.com).
One caution: methylene blue tends to overestimate viability at lower values and is recommended when viability is expected >90% (www.brewiki.org). If viability falls below ~80–90%, many brewers scrap the yeast or salvage minimal amounts; Fal Allen notes tests become unreliable below ~80%, and yeast under ~80% viability should only be used as a last resort because dead cells can cause off‑flavors and harbor anaerobes (www.morebeer.com). Other dyes like methylene violet or fluorescent stains, plate plating (days), or flow cytometry with dual stains are also used, but rapid staining is common in production (www.brewiki.org).
Hemocytometer counting method
On a standard hemocytometer, each large square holds 0.0001 mL (9 large squares cover 0.1 mm³). Dilute to yield a few dozen cells per square, load the chamber, and count cells in multiple large squares (e.g., 5) to reduce error (microbebrewer.blogspot.com). Then compute: cells/mL = cells counted ÷ volume counted (mL). Example: 200 cells in 5 large squares (0.0005 mL total) equals 4×10^5 cells/mL in the diluted sample; multiply by the dilution factor to get the original slurry concentration. A handy rule: cells per large square ×10,000 = cells/mL (microbebrewer.blogspot.com).
Perform viability and counts on the same dilution to derive viable cell density (cells/mL). Live cell count = total cells × viability fraction. From there: Pitch volume (mL) = Target viable cells ÷ Viable cells/mL.
Pitch rate standards and examples
Most guidelines specify viable cells per mL of wort per degree Plato (°P = sugar concentration). A common rule is ~1.0×10^6 viable cells/mL per °P for ales, and ~1.5–2.0×10^6 for lagers; Wyeast lists 0.5×10^6 for very low‑gravity beers up to 1–1.5×10^6 for high‑gravity ales (wyeastlab.com). For a 12°P wort (≈1.048 SG), the target is ~1.2×10^7 cells/mL. If the slurry measures 1×10^8 viable cells/mL, pitch ~120 mL per liter of wort to hit that target, adjusting for high gravity or cold temperatures; some sources recommend 1.5×10^6 per °P for lagers (wyeastlab.com).
Viability standards are strict: many breweries reject slurry below ~90% viable, aiming for ≥90–95% viability; if necessary, they pitch additional volume to compensate (www.brewiki.org).
Consistency and records
Record each yeast lot’s count and viability, and calculate pitch volumes batch by batch. The method matters as much as the math: the same dilution and count protocol every time yields reproducible fermentations and flavors over many generations (wyeastlab.com; wyeastlab.com; www.brewiki.org).
