Stuck Pinot Noir Fermentation with a Bottling Deadline
A 6,000-litre stainless-steel tank of Pinot Noir (clone 777, Willamette Valley) was inoculated with EC1118 at 20 °C after settling. Initial sugar was 28.8 °Brix, pH 3.55, YAN 140 mg/L, and the winemaker added 60 g/hL DAP at one-third sugar depletion. On day 12 the density has been stable for 72 hours at 8 g/L residual sugar, temperature has drifted to 26 °C, VA is 0.45 g/L, and there is no obvious H2S yet. The tank must be emptied in 10 days for a Chardonnay pressing, and the private-label client wants the wine bottled on schedule. The cellar has pad filtration (1 µm nominal), no cross-flow, and no Velcorin. The winemaker proposes adding another 100 g/hL DAP, chilling to 18 °C, and bottling with 8 g/L RS as an off-dry wine after a 1 µm pad filtration and 30 mg/L free SO2. The client has already approved an off-dry style but has not been told about the fermentation stall.
1. Diagnose the most likely causes of the stall and identify the two decisions that most affect the outcome.
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The starting YAN of 140 mg/L is low for 28.8 °Brix; a rough working target is 1.2–1.5 times the Brix in YAN, so this must was already nutrient-limited before ethanol became inhibitory. Adding 60 g/hL DAP at one-third sugar depletion was late: yeast cannot assimilate DAP efficiently once ethanol is high, and excess DAP at this stage can feed spoilage organisms and raise VA rather than finish the fermentation. The temperature drift to 26 °C is within EC1118’s range but adds stress and increases the chance of sluggishness and volatile acidity; the stable density for 72 hours with 8 g/L RS confirms a true stall, not a slow patch. The two critical decisions are: first, whether to attempt a restart or to stabilise the wine as it is; second, if restarting, whether to use a rehydration nutrient plus a fresh yeast acclimatised to ethanol, not more DAP. The proposed 100 g/hL DAP is the wrong tool at this point. The absence of H2S is good but not reassuring about refermentation risk.
2. Design a restart protocol using only the resources in the cellar, including yeast rehydration, nutrient choice, temperature, and monitoring thresholds.
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Use a fresh active dry yeast with good ethanol tolerance, rehydrated at 35–40 °C in water containing a rehydration nutrient at about 1.25 times the yeast weight; do not rehydrate in must. Acclimatise the yeast by adding tank wine in small steps over 20–30 minutes until the mixture is within about 5 °C of the tank, avoiding cold shock. Add the restart culture at 30–40 g/hL and add an organic yeast nutrient rather than DAP, split between the restart and roughly 4 g/L RS. Hold the tank at 20–22 °C, not 18 °C, with gentle pumpovers to keep yeast in suspension without oxygen pickup. Monitor density twice daily, plus VA and H2S daily. Set a decision threshold: if density has not fallen by at least 5–8 g/L within five days, stop the restart and move to stabilisation. Keep the tank topped and protected with inert gas, and do not add sulfite until the restart outcome is known.
3. If the restart fails, advise the winemaker on whether the proposed bottling plan is defensible, and what to tell the client.
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The proposed bottling plan is not defensible. Eight grams per litre of residual sugar with 30 mg/L free SO2 at pH 3.55 gives very little molecular SO2 and no reliable protection against refermentation. A 1 µm nominal pad filter is not an absolute sterile filter and will not reliably remove all yeast, especially from an unfiltered, nutrient-stressed red. The predictable outcomes are bottle refermentation, haze, rising pressure, and off-flavours, plus a client complaint far more expensive than a delayed shipment. Defensible options are: restart to dryness; or, if the off-dry style is retained, use absolute sterile filtration (0.45 µm or tighter, validated), cold stability testing, and a preservative strategy appropriate to the pH and style, with laboratory confirmation before release. The client must be told now that fermentation stalled, the cause, the revised timeline, and the two options. Presenting the delay as a quality decision with analysis is far better than shipping an unstable wine.