Pale Ale Stuck at 1.020 Before a 400-bbl Order
A 15-bbl brewhouse is producing a 1.052 OG pale ale with a target of 78% apparent attenuation (FG 1.011). The last batch finished at 1.020 after four days, was crashed to 34°F, dry hopped at 2 lb/bbl for two days, and packaged. The beer is hazy, sweet, and shows a strong diacetyl note. Brewing records say: mash at 67°C for 60 min, 10% crystal 60, yeast pitched at 18°C at 1.0 million cells/mL/°P, wort oxygenated to 8 ppm, fermentation free-rises to 21°C, then crash-cools on day 4 when gravity is 1.022. You have a 400-bbl order due in 10 days and a fresh yeast brink available. The beer cannot be sold as the target pale ale in its current state.
1. Calculate apparent attenuation and expected FG, then diagnose the gap.
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Apparent attenuation = (OG – FG)/(OG – 1) × 100 = (1.052 – 1.020)/0.052 × 100 = 61.5%. Target 78% would give FG = 1.052 – 0.78(0.052) = 1.0114, so the batch is about 0.009 gravity points too high. That is a fermentation and attenuation failure, not a small miss. The beer is sweet and hazy, consistent with residual dextrins, yeast in suspension, and early crash. Diacetyl confirms yeast was removed or went dormant before VDK reduction. The 67°C mash and 10% crystal 60 explain some unfermentable extract, but not the full gap; crashing at 1.022 on day 4 is the bigger process error.
2. Identify the most likely causes and explain which are fixable after the fact.
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Likely causes: (1) crash-cooling at 1.022 before fermentation finished and before a diacetyl rest; (2) high mash temperature and crystal malt raising unfermentables; (3) possible yeast stress, though 8 ppm oxygen and 1.0 million cells/mL/°P are adequate if viability is good; (4) dry hopping at 20°C may have introduced hop creep, but the beer was already at 1.020. The haze is likely yeast and polyphenol, not necessarily a fault. Diacetyl is a VDK problem and is partly fixable by warming and rousing. Sweetness is residual extract and is not fixable by warming alone. You can reduce diacetyl and maybe gain a few gravity points, but you cannot turn this into the target 1.011 beer without blending or rebrewing.
3. Decide whether to release, remediate, or blend. Give a 10-day plan for the 400-bbl order.
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Decision: do not release as the target pale ale. Remediate first: warm the tank to 20–21°C, rouse with CO2, add fresh viable yeast from the brink if healthy, and hold until VDK is below sensory threshold, targeting under 10–15 ppb and a stable gravity. Test daily. If gravity drops to 1.014–1.016, the beer may be acceptable as a sweeter pale ale, but not as the 1.011 target. With 400 bbl due in 10 days, plan a blend with a drier batch or rebrew; do not dry hop again until VDK is resolved. Package only after forced VDK and micro checks. Communicate any style or body change if blending, and hold back the current dry-hopped portion if diacetyl persists.