Nitrogen management emerges as key factor in modern American winemaking

In the world of winemaking, nitrogen plays a central role in the fermentation process. This element is essential for yeast health and activity, directly impacting the quality of the final wine. The need to monitor and control nitrogen levels has become a standard practice in wineries across the United States and around the world.

Yeast, the microorganism responsible for converting grape sugars into alcohol, requires more than just sugar to thrive. Nitrogen is one of its most important nutrients. Without enough nitrogen, yeast can struggle to complete fermentation, leading to delays or even stuck fermentations. These issues can result in the production of hydrogen sulfide (H2S), a compound that gives off unpleasant sulfur odors and can spoil the aroma and taste of wine.

Grape musts—the freshly pressed juice containing skins, seeds, and stems—often lack sufficient nutrients for yeast, especially nitrogen. This deficiency is more common in grapes from vines under stress, such as those experiencing drought, mineral shortages, or disease. Certain grape varieties like Cabernet Sauvignon, Merlot, Zinfandel, and sometimes Chardonnay or Riesling are also more prone to low nitrogen levels. Wineries with a history of slow or problematic fermentations pay close attention to these risks.

To address this challenge, winemakers routinely measure the amount of Yeast Assimilable Nitrogen (YAN) in must before fermentation begins. YAN includes both amino nitrogen (measured by NOPA tests) and ammoniacal nitrogen. Another test called FAN measures only amino acid-based nitrogen compounds. Accurate measurement is critical because once yeast starts growing—whether it’s a commercial strain or wild yeast—the results no longer reflect the original must composition.

The recommended YAN range for healthy fermentation is typically between 200 mg/l and 400 mg/l. Musts with higher sugar content require more nitrogen because yeast needs extra nutrients to process the additional sugar. If a must is at risk for nitrogen deficiency or a stuck fermentation, winemakers may add 50 to 100 mg/l of extra nitrogen per degree Brix above normal sugar levels. There are established tables and algorithms to help calculate precise additions.

Adding too much nitrogen can be as problematic as having too little. Excessive nitrogen can cause fermentation to proceed too quickly at first, raising temperatures that may stress or kill yeast cells. It can also lead to salty flavors in wine or increase levels of ethyl carbamate—a compound considered carcinogenic—in the finished product.

Timing is another key factor in nutrient management. Winemakers add nutrients at specific points during fermentation to maximize their effectiveness and ensure yeast can use them efficiently. Commercial nutrient blends often contain both forms of nitrogen along with minerals and yeast hulls to provide a balanced supply.

Highly clarified or filtered musts are particularly vulnerable to nutrient deficiencies because many natural nutrients are removed during processing. Wines undergoing spontaneous fermentation without added yeast also face higher risks since native yeasts may have different nutritional needs.

The careful measurement and adjustment of nitrogen levels have become routine steps in modern winemaking. Laboratories within wineries or third-party labs perform these analyses before fermentation begins each season. The goal is always the same: support healthy yeast growth, avoid off-flavors caused by sulfur compounds, and produce wines that meet high standards for aroma and taste.

As scientific understanding of fermentation deepens, winemakers continue refining their approaches to nutrient management. The balance of nitrogen remains a delicate but vital part of producing quality wines that reflect both tradition and innovation in American viticulture today.