Arrested Fermentation

During alcoholic fermentation, yeast turn grape sugar into alcohol. Arresting fermentation means stopping that process on purpose, before all the sugar is used up. The OIV's International Code of Oenological Practices defines the practice as arresting the alcoholic fermentation, with the objective of a product containing the grape's own sugar. That leftover sugar is called residual sugar, measured in grams per litre. Stopping early also keeps alcohol down: such wines are usually under 10% abv with some sweetness on the palate. With late-picked German Riesling, for instance, fermenting all the sugar might give a dry wine of around 13% abv, while interrupting the fermentation gives a wine of 8% abv that tastes sweet, balanced by Riesling's high acidity.

• Goal: keep natural grape sugar in the finished wine
• Side effect: lower alcohol than a wine fermented fully dry
• Balance: in Riesling, high acidity can make an off-dry wine taste dry

Under the OIV code, only physical techniques may be used for this practice: heat, cold, filtration and centrifugation. Centrifugation, like filtration, is listed elsewhere in the code as a way of separating clear liquid from the solid matter suspended in it. One sequence is to cool the ferment and then filter out the yeast, as for Moscato d'Asti. Cold can simply hold a fermentation: under the OIV code, must may be cooled to avoid the start of fermentation, and in the ancestral sparkling method the first fermentation is temporarily suspended, usually by cooling the liquid, and concluded after the wine is bottled. Under the code, the product obtained shall remain fermentable. Because leftover sugar can trigger re-fermentation in the bottle, producers either ferment out all the fermentable sugar or remove the yeast by sterile filtration at bottling.

• Cold can hold or suspend a fermentation
• Filtration or centrifugation takes the yeast out
• Sterile filtration at bottling guards against re-fermentation

Mutage reaches a similar goal by a different route. Wine spirit or rectified alcohol is added to must before or during fermentation, with the aim of stopping fermentation to obtain a fortified wine. Adding grape spirit or sulphites to kill the yeast, as for Ruby Port and vins doux naturels, is a different method from cooling and filtering, as for Moscato d'Asti. Arrested fermentation without spirit therefore leaves a light, low-alcohol wine rather than a fortified one.

• Mutage: spirit added, yeast killed, wine fortified
• Physical arrest: no spirit added, alcohol stays low

A stuck fermentation is the opposite of a choice: an alcoholic fermentation that stops before the winemaker wants it to. It is often caused by a lack of nitrogen in the grapes, which yeast need to grow, and very ripe grapes can also cause trouble, since their high sugar leads to high alcohol that challenges the yeast. Fermentation temperatures that are too high or too low are another cause. The risk is real: part-fermented must is prone to bacterial spoilage and oxidation, and stuck fermentations can be very difficult to restart. The difference is intent: an arrested fermentation is stopped when the winemaker chooses, a stuck one before the winemaker wants it to.

• Arrested: planned, timed, followed by yeast removal
• Stuck: unplanned, often linked to nitrogen shortage, high alcohol or temperature
• Prevention of stuck fermentation includes nitrogen additions and resistant cultured yeasts

Moscato d'Asti shows the method in action. It relies on a partial fermentation under pressure in tank, so carbon dioxide is not lost; once alcohol reaches 5% abv, the wine is chilled and filtered to remove the yeasts, giving a slightly fizzy wine sweetened by unfermented grape sugar. The rules set a minimum of 4.5% and a maximum of 6.5% alcohol, residual sugar of roughly 80 g/l, and no more than 2.5 atmospheres of pressure. Sparkling Asti DOCG also relies on controlled stops: once the first fermentation reaches 5% alcohol the temperature is reduced to hold the wine, and fermentation is later arrested when foam begins to form, finishing at 7% to 9.5% abv. In German wine, when fermentation is interrupted before the end, for example by cooling, natural grape sugar remains in the wine. Kabinett Riesling usually carries some residual sugar yet may taste dry because of its high acidity.

• Moscato d'Asti: one fermentation, chilled and filtered at about 5% abv
• Asti DOCG: fermentation arrested when foam begins to form
• German off-dry Riesling: fermentation interrupted, for example by cooling

Facts in this article were checked against the primary sources below. Last verified 2026-10-05.

• https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/musts/interruption-of-alcoholic-fermentation-by-physical-procedures
• https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/musts/preservation-with-alcohol-before-or-during-fermentation
• https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/musts/alcoholic-fermentation
• https://www.oiv.int/node/3676
• https://www.decanter.com/learn/residual-sugar-46007/
• https://www.decanter.com/learn/frizzante-it-44392/
• https://www.wsetglobal.com/media/1426/articles-2013_-asti.pdf
• https://italianwinecentral.com/denomination/asti-docg/
• https://www.winesofgermany.com/our-wine/wine-tasting/wine-tasting/195/geschmacksrichtungen
• https://www.wsetglobal.com/knowledge-centre/blog/2024/july/17/understanding-riesling-in-germany
• https://www.decanter.com/learn/what-is-stuck-fermentation-ask-decanter-410477/
• https://www.oiv.int/standards/international-code-of-oenological-practices/part-ii-oenological-treatments-and-practices/musts/settling
• Last verified 2026-10-05