A Syrah fermentation stuck at 18 g/L with six weeks to sale
A 4,000 L stainless tank of destemmed Syrah is fermenting with a commercial yeast. Starting sugar 25.6 °Brix (potential about 14.8% alcohol); YAN measured at 110 mg/L; no nutrient was ever added. Temperature ran 24-26 °C, then was dropped to 19 °C on day 6 to protect aromatics. On day 9 density has been flat at 1.008 - roughly 18 g/L residual sugar - for 72 hours. VA 0.42 g/L, no H2S or mercaptans on the nose, no film, the cap still smells clean and fruity. The tank is 15% ullaged and has been unprotected since this morning's punchdown. A second 4,000 L tank of the same wine went dry in seven days. A bulk buyer wants 14.5% alcohol and a dry wine in six weeks.
1. Diagnose the most probable causes and rank them. What would you check before you act?
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Ranked:
- Nitrogen depletion. 110 mg/L YAN against 25.6 °Brix is well short of what a healthy ferment needs (a common target is roughly 200+ mg/L for this ripeness). The yeast ran out of building blocks at the point where alcohol is becoming toxic.
- Temperature drop to 19 °C. Lowering temperature to protect aromatics at day 6 is a real cause of sluggishness: at 14%+ alcohol, yeast needs warmth to finish.
- Oxygen and sterol limitation. No aeration, a dense must, and 15% ullage all work against the last few grams of sugar.
Check first: actual residual sugar by an accurate method (not just hydrometer/density), yeast viable count, free and total SO2, and the temperature probe against a second thermometer. Rule out inhibition - a sulfite addition, a pesticide residue, a sanitizer residue. Then top the tank up or gas it: 15% ullage with an active cap is your immediate oxidation and volatile acidity risk, and it is the one thing that costs nothing to fix tonight.
2. Design a restart protocol. What would you deliberately not do?
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Protocol
- Warm the tank to 22-24 °C and hold it there for 24 hours before doing anything else.
- Add inactivated yeast hulls/autolysate (roughly 20-40 g/hL). They adsorb inhibitory medium-chain fatty acids and supply sterols and survival factors.
- Build an acclimatised starter, not a straight inoculation. Rehydrate a high-alcohol-tolerant strain with a rehydration nutrient at about 40 °C, then step tank wine into the starter, doubling the volume every 2-3 hours and keeping the temperature difference under 10 °C, until the starter is 5-10% of the tank volume. Only then inoculate.
- Keep the cap wet, monitor density twice daily, and add a second dose of yeast hulls if the rate flattens.
Do not: add DAP now - yeast cannot assimilate ammonia at high alcohol and you will feed spoilage organisms; aerate or splash-rack - you will oxidise and make VA; add sulfite - it will inhibit the restart you are trying to start; drop temperature again for aromatics - finish first, style second.
3. The restart fails and the wine is still at 12 g/L RS at 14.7% alcohol with six weeks to go. What are your options and how do you rank them?
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Ranked by risk and cost:
- Blend down into the dry tank. 12 g/L in tank A, 0 g/L in tank B. A 1:3 blend (A:B) gives about 3 g/L, comfortably under the usual 4 g/L 'dry' perception threshold, and both wines are near 14.7% so alcohol is not diluted much. It is cheap, immediate, and it consumes your dry wine - so check the maths against the total volume the buyer actually wants.
- Sterile filtration (0.45 micron) and sell it as a slightly off-dry wine. Works technically, but it strips texture, costs money, and the buyer has asked for dry - do not do it silently.
- Talk to the buyer now. A six-week window is long enough to renegotiate a specification; it is not long enough to recover from a refermentation in bottle or an unplanned filtration at the last minute.
Do not bottle at 12 g/L without sterile filtration. Residual sugar plus 14.7% alcohol is a refermentation risk in the customer's cellar, and that failure lands on you, not the buyer.