Off-notes in whisky: sulphur, feints and how distillers trace them
Off-notes in whisky come from somewhere specific: the yeast, the still, the cut or the cask. Distillers who can name them can trace them. Tracing is how quality improves.
Why off-notes matter for a distiller
A small amount of sulphur or feints can be part of a distillery's character. Too much and the whisky tastes dirty, heavy or simply wrong. Problems that start in new make spirit can take years to show up fully, so catching them early is vital.
The good news is that most off-notes leave clear fingerprints. Each one comes from a specific step. Train your nose to recognise them and you can fix the cause rather than hoping the cask hides it. Our guide to getting new make spirit right covers the process side.
Sulphur: struck match, cabbage, meaty
What you notice. Struck match, boiled cabbage, rotten egg, rubber or a meaty, savoury note. At low levels it can read as weight and richness.Where it comes from. Yeast produces sulphur compounds during fermentation, more so when stressed by heat, low nutrients or poor oxygen at pitching. Copper in the still removes many of them. Sulphur in new make usually means too little copper contact: a fast run, worn or fouled copper, or a condenser design that limits contact. Worm tub condensers, for example, give less copper contact and a heavier spirit.Sherry casks. Some sherry casks were cleaned with burning sulphur candles. That can add a struck match note to whisky matured in them, quite separate from any new make problem.Feints: heavy, oily, sweaty
What you notice. Wet cardboard, leather, tobacco, sweaty or cheesy notes and an oily, heavy mouthfeel. Some feints read as honey or beeswax at low levels.Where it comes from. Feints are the heavier compounds that come over late in the spirit run, as the strength falls. Cutting to feints too late lets them into the heart. Running the spirit still too hard can also smear the cut, pushing heavy compounds over earlier.The fix. Review your cut points, by strength and by nose. Many distillers smell the spirit run at regular intervals as it approaches the feints cut and adjust the cut strength based on what they find, not a fixed number alone.Heads and other notes
Solvent and nail polish. Ethyl acetate and other volatile compounds from the start of the run. Too much in the heart means the foreshots cut was too early. It can also signal a fermentation that picked up bacteria or ran too long and warm.Sour or vinegar notes. Often bacterial contamination in the wash, particularly in long, warm fermentations in Indian conditions.Burnt or cooked notes. Solids scorching on a directly heated still. Check that wash solids are managed and heating is even.How distillers trace an off-note
A disciplined approach looks like this:
- Smell and taste the new make diluted to around 20% ABV, which makes off-notes far easier to spot.
- Check whether the note appears in every batch or only some. Batch-to-batch issues usually point to fermentation.
- Look at the spirit run log: cut strengths, run rate and temperatures.
- Sample the spirit run at intervals and smell each sample to see where the note appears.
- Compare washbacks, yeast lots and fermentation times for problem batches.
- For matured whisky, compare the new make with the cask sample to see whether the cask added it.
Record everything. A pattern across ten batches tells you more than one memorable bad one.
Building a sensory routine
Off-notes are easier to catch when the same small panel tastes the same samples on a schedule, using the same words. Train the panel with reference samples. Spiked standards are available for many common compounds. Our guide to phenolic off-flavours shows how beer brewers handle similar faults. The methods carry across well.
Agree a scale for intensity and a pass or fail threshold for new make. That stops a borderline batch from slipping into a cask because nobody wanted to say it out loud.
Fermentation in Indian heat
Many off-notes start in the washback rather than the still. In an Indian summer an uncooled washback can climb well past the low 30s °C. Hot, stressed yeast makes more sulphur compounds and more heavy alcohols. Warm wash left standing invites bacteria. Logging washback temperature every few hours, with a clear upper limit and cooling to hold it, removes a large share of the problems a distiller would otherwise chase at the still.
Prevention beats correction
Clean washbacks, healthy yeast, sensible fermentation temperatures, well-maintained copper, a steady still run and consistent cuts prevent most off-notes. A cask can soften some sulphur over years, but it cannot remove feints. Get the spirit right first.
Common questions
What causes sulphur notes in whisky?
Mainly yeast producing sulphur compounds in fermentation, with too little copper contact in the still to remove them. Some sherry casks can add sulphur too.
What are feints in whisky?
Heavy compounds that come over late in the spirit run. If the cut is made too late they give oily, leathery or sweaty notes.
Why do distillers dilute new make to taste it?
At around 20% ABV the alcohol burn drops and off-notes become far easier to smell.
