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A stuck fermentation occurs in brewing beer or winemaking when the yeast become dormant before the fermentation has completed. Unlike an "arrested fermentation" where the winemaker intentionally stops fermentation (such as in the production of fortified wines), a stuck fermentation is an unintentional and unwanted occurrence that can lead to the wine being spoiled by bacteria and oxidation. There are several potential causes of a stuck fermentation-the most common are excessive temperatures killing off the yeast or a must deficient in the nitrogen food source needed for the yeast to the thrive. Once the fermentation is stuck, it is very difficult to restart due to a chemical compound released by dying yeast cells that inhibit the future growth of yeast cells in the batch. At the winery winemakers take several steps to limit the possibility of a stuck fermentation occurring, such as adding nitrogen to the must in the form diammonium phosphate or using cultured yeast with a high temperature and alcohol tolerance. These steps that winemakers may take to prevent a stuck fermentation will each have their own subtle or dramatic effect on the resulting flavors and quality of the wine.
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Prevention techniques
There are various techniques that a winemaker can employ to minimize the chances of a stuck fermentation happening. The most common is to used a cultured yeast strain with a high alcohol and high temperature tolerance coupled by diligent control of the fermentation temperature. Another technique is to add yeast nutrients, include nitrogen, to the must. The ammonium salt diammonium phosphate is a popular inexpensive means of ensuring the must has sufficient nitrogen. Whatever technique the winemaker uses, each has the potential to subtly or drastically affect the resulting flavor and quality of the wine.
References
- ^ J. Robinson (ed) "The Oxford Companion to Wine" Third Edition pg 664-665 Oxford University Press 2006 ISBN 0198609906