It's November, the cellar is a good 12 degrees, and your airlock hasn't made a peep in three days. In exactly this moment the beginner tends towards the greatest folly: he tears open the demijohn and tips in a new sachet of yeast. I did that myself in 1994, with an apple wine that was too slow for me. Afterwards I had not one problem but two: the stalled batch and a second load of yeast that drowned in the cold must just like the first. Throwing fresh yeast into a hostile environment without knowing the cause is burning money. Let's do this differently, in order.
First check: is the fermentation really stalled?
Before you rescue anything, measure. A silent airlock doesn't automatically mean a stuck fermentation. Maybe the yeast is simply finished and has eaten up all the fermentable sugar. Take the must hydrometer or the refractometer and read the must weight. If the wine is dry (with most batches around or below 0 °Oechsle, or with the refractometer in the low range with the typical alcohol distortion), then it's through and you're chasing a problem that isn't one. But if the hydrometer still shows clear residual sweetness and nothing is happening, then the fermentation really is stalled. Note down the value. Without this number you work blind.
The emergency plan in this order
The order is no accident. It goes from the cheapest and most likely to the most laborious. Work it from top to bottom and don't skip.
- Check the temperature. In nine out of ten cases this is the culprit, especially in autumn and winter. Wine yeast is happy between about 18 and 24 degrees. Below 15 degrees it turns sluggish, below around 10 degrees it lies down to sleep and doesn't stir any more. A cellar floor at 11 degrees is quite enough to bring a batch to a standstill. Too hot works too: above 30 degrees the yeast gets into stress, forms off-flavours and in extreme cases dies off. So stand the demijohn warm, but not on the heating. A quiet spot at a steady 20 degrees is worth gold. Important: warm the whole thing up slowly, over hours, not with the hairdryer. Often the airlock starts bubbling again by itself after half a day, and you're done.
- Remedy a nutrient shortage. If the fermentation doesn't restart despite the right temperature, the yeast is usually short of nitrogen. Especially with fruit wines from sugar-rich but nutrient-poor fruits (apples, berries, lots of added household sugar) the yeast starves. Then yeast nutrient helps, at its core diammonium phosphate, which supplies the yeast usable nitrogen. Dissolve the dose as per the pack instructions in a little warm water or must and stir it in. Then give it a day's time. A combination preparation with additional vitamins is often the better choice for finicky batches than plain salt, because the yeast then also gets the missing thiamine.
- Is the alcohol already too high? Now comes the honest question. Work out roughly, from your starting must weight, the alcohol already fermented. Most normal wine yeasts throw in the towel somewhere at 14 to 15 % vol, that's their biological limit, not a fault. So if you started a heavy batch with lots of sugar and the yeast stopped at 15 percent, then it isn't sick but exhausted. No nutrient and no warmth in the world gets a yeast over its alcohol tolerance. In that case you need a more robust variety, and properly introduced. On to step four.
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Set up a fermentation starter with robust yeast and feed it in slowly. This is the actual craft step, and here rescue parts ways with tipping in. Take a resilient cultured yeast. For stalled wines a Bayanus yeast like the Bordeaux is ideal, it keeps working even at cooler temperatures and tolerates more alcohol. With strong fruit mashes I reach for the distiller's mash yeast, which is made for hard conditions. This is how the starter goes:
- Rehydrate the dry yeast as per the pack instructions, usually in lukewarm water, never cold and never boiling.
- Set up a small starter: about 200 to 300 ml of lukewarm water or diluted must, a pinch of nutrient, temperature around 20 degrees. Wait until it visibly foams and smells. That takes a few hours.
- Now the crucial part: add only roughly the same amount of your stalled wine at first. Wait until the starter has digested that and gets going again. Then you double it again, and again. Over one to two days you accustom the young yeast to the alcohol in stages, until you've mixed in the whole batch.
- Turbo yeast as the very last resort. If even the patiently built-up starter gives up, the turbo yeast remains. It's bred for high alcohol yield and speed and forces through a batch that normal yeast fails at. I deliberately say last resort: turbo yeasts work hot and fast and rarely deliver the finest aroma. For a wine you actually wanted varietal and clean, that's a compromise. For a mash that's meant to be distilled anyway or intended as a strong batch, or when the alternative would be pouring it away, it's exactly right. Here too: first a starter, then feed in, don't pour blindly.
What you must never do
Don't tip dry yeast straight into the stalled batch. I know, it's the first reflex, and the sachet is right there. But the new yeast lands in the same too-cold, nutrient-empty or too-alcoholic milieu that killed the first. Without a culture and without acclimatisation it dies just the same, and you've lost time, money and another sachet. Diagnosis before therapy, always in this order. And one more thing from painful experience: keep hygiene high while the wine stands still. A stalled batch with residual sugar and without active fermentation is a feast for acetic bacteria. My acetic spoilage of 1998 began exactly like that, with a wine that stood unprotected and silent in the cellar for two weeks.
A word on origin
The distiller's mash and Bordeaux strains I recommend here come from the Kitzinger tradition. The pharmacist Paul Arauner began in Kitzingen in 1897 to bring cultured yeasts and cellar supplies to the people, and the Kitzinger Wine Book reached over 750,000 households. The business there closed at the end of May 2024. We carry on this knowledge and the remaining original products by mail order from Aachen. So you're not buying just any yeast, but one with a very long history of dealing with exactly such problem fermentations.
What I use myself
For the classic stalled wine I reach for the Kitzinger Bordeaux dry yeast, because it manages the restart most reliably in a cooler cellar and at higher alcohol, provided you set it up as a starter and feed it in. On top of that, if the fruit was nutrient-poor, I add yeast nutrient, otherwise even the most robust yeast starves. For strong fruit mashes the distiller's mash yeast is the right choice, and the turbo yeast I really keep for the case where nothing else works any more. Don't buy everything at once. Start at step one, the thermometer. That costs you nothing but half a day's patience, and patience is half the battle in the cellar anyway.
From the cellar, Magnus