The wine production process, one of the oldest human traditions, has in its essence a scientific complexity. At the heart of this process is nitrogen, an element that plays a crucial role in the fermentation of wine. However, despite its importance, nitrogen can cause wine quality problems if not managed properly.
In addition to sugar, all yeasts need nitrogen for their development. Keeping yeasts alive during fermentation is not a simple process, since grape musts are often deficient in one or more nutrients necessary for them. These deficiencies can cause fermentation delays or stops, or the production of hydrogen sulfide (H2S), generating unwanted volatile sulfur compounds in the wine after fermentation, which can result in a wine with defects and bad taste.
Therefore, it is essential to ensure that the yeasts have enough nitrogen to survive and ferment efficiently. Current winemaking practices account for these deficiencies by adding nitrogen-based nutrients during fermentation. However, an excess of nitrogen can have detrimental consequences. Fermentation can be too fast in the initial periods, reaching temperatures that can stress or even kill the yeast. Also, an excess of nitrogen can cause a salty taste in wine due to the production of sulfides and ethyl carbamate, a carcinogenic compound.
Therefore, it is crucial for winemakers to measure the amount of nitrogen present in the must and adjust the levels according to the needs of the yeasts. Yeast Assimilable Nitrogen (YAN) is a commonly used measure. YAN is the total nitrogen in the wort available to the yeast, including both alpha amino-nitrogen (amino-N), which is measured by the NOPA test, and ammoniacal nitrogen (ammoniacal-N).
To measure amino-N nitrogen levels, another test called FAN can be used. However, it is important to note that both the NOPA and FAN tests only measure amino acid-based nitrogen complexes and not ammoniacal nitrogen. Nitrogen results, both ammoniacal-N and amino-N, are only valid if determined before any yeast growth, whether inoculated or native.
Yeasts generally need between 200mg/l and 400mg/l of nitrogen to complete fermentation without problems. This amount can vary depending on the sugar content in the must, with a greater amount of nitrogen being necessary for musts with high sugar levels. If the must presents a higher risk of nitrogen deficiency or the possibility of a stoppage in fermentation, between 50mg/l and 100mg/l of additional nitrogen should be added for each additional brix degree of sugar (approximately). There are tables or algorithms that allow you to calculate the amount accurately.
Musts at high risk of nitrogen deficiencies and stopped fermentations are those with high sugar levels, vines with water stress, mineral deficiencies (such as nitrogen), low vigor or diseases, vineyards with a history of slow, stopped or forming fermentations of H2S, highly clarified, filtered or refined musts, musts that will have a natural fermentation (without inoculating yeasts), musts with malolactic fermentation during alcoholic fermentation and some grape varieties such as Cabernet Sauvignon, Cabernet Franc, Merlot, Zinfandel and, in some occasions, Chardonnay, Syrah and Riesling.
It is critical to add nutrients to the yeast at specific times during fermentation to maximize their effectiveness. Yeasts require both ammonia nitrogen and amino nitrogen, which can be obtained from nitrogen complexes containing amino acids. Commercial amino acid complexes, which often contain yeast extracts, minerals, and yeast husks, are an excellent choice to ensure proper nutrient balance.
In short, the proper balance of nitrogen is crucial for the wine fermentation process and the final quality of the product. Lack of or excess of this nutrient can cause serious problems, from stopped fermentation to the production of off-flavored wines. Therefore, a correct measurement and control of nitrogen during fermentation is essential for the production of high quality wines.
