Adequate nutrition, in the form of nitrogen, is required for proper fermentation to occur. Yeast assimilable nitrogen (also known as yeast available nitrogen or YAN) analysis is conducted on juice at harvest to indicate the level of nitrogen available at the start of fermentation.
Nitrogen is an essential nutrient required for yeast health during the fermentation process. The YAN value for a given lot of juice directs winemakers on nutrient addition decisions throughout the duration of primary fermentation. Supplementation of nitrogen to a fermentation should help minimize the potential risk of hydrogen sulfide production.
Although there are differences in what nutrient suppliers consider a "high," "medium," and "low" YAN concentrations, the general principle among all suppliers is the same: use the initial YAN concentration and starting Brix value of the juice/must in order to determine proper nutrient supplementation throughout primary fermentation.
Additionally, winemakers should also consider and double check the yeast strain selection, as some yeasts have higher nitrogen requirements than others. Penn State Extension Enology recommends following supplier guidelines for specific nutrient additions.
The purpose of this article is to show the variation in YAN values for a wine grape variety within a single vineyard (located in Pennsylvania or New York state) across several vintage years. Data was collected by a single winery in Pennsylvania and values were not analyzed for statistical purposes (i.e., no reps were run for each analysis).
It should be noted that YAN values were determined using the Formol Titration method until 2011, at which point some of the varieties were tested enzymatically. (The result differentiation between these two methods was not found to be significantly different. Statistical evaluation of these analytical methods was completed by the industry member.)
At the conclusion of this article, a list of additional resources pertaining to YAN, YAN analysis, and hydrogen sulfide formation are included.
How to Read the Graphs in this Article
The following is an explanation regarding how the charts in this paper should be read:
The YAN content (mg Nitrogen/L, Nitrogen may be abbreviated as "N") is indicated on the "Y" axis. The "X" axis contains a wine grape or fruit variety of a particular vineyard plot in which the YAN concentration has been measured. A numeral (1-4) follows the variety name, which denotes the region where the grape variety or fruit was grown:
- Represents a vineyard from Southeastern Pennsylvania
- Represents a vineyard from Long Island in New York
- Represents a vineyard from the Finger Lakes in New York
- Represents a vineyard from the Lake Erie Region in Northwestern Pennsylvania
There are a group of colorful bars above each variety name and regional designation; each bar represents a different harvest year. The key to identify each color with a specific vintage year can be found on the right hand side of the graph.
A total of 6 years of YAN evaluation has been recorded. However, some varieties do not contain all 6 years of data. This is represented by an absence of the bar on the chart. In the example above, we can see that for "Chardonnay 4" data was not collected in the years 2006 and 2009.
The two dashed red lines that flow horizontally within the graph indicate the general "minimum" and "maximum" values to indicate the difference between "Low" and "High" YANs. For the purpose of this report, anything below 125 mg N/L is considered a low YAN content. Any number above 225 mg N/L is considered a high YAN content. Anything in between those two dashed red lines is considered a medium YAN content.
The purpose of documenting the low, medium, and high baseline YAN levels within the graph is to show how YAN concentration can vary between these levels from year-to-year. This is important, as low, medium, and high YAN levels require different nutrient addition strategies during primary fermentation to maintain yeast health. For more information on nutrient addition strategies during fermentation, please refer to the Penn State Wine Made Easy Fact Sheet: Nutrient Management .
YAN Data from 2006 - 2011 in PA and NY Wine Growing Regions
The following graphs contain several years of YAN values for a specific wine grape variety. Each variety identified is grown and produced from one particular grower and fruit is taken from the same vineyard each year for analysis.
The objectives of these graphs are to show the variation in YAN values for a specific variety over the course of several years, and provide justification for measuring YAN each vintage.
Graph 1 shows YAN data from 2006-2011 for Chardonnay, Niagara, Apple, Cayuga, Traminette, and Vidal Blanc varieties produced in Pennsylvania.
As one can see from Graph 1, the YAN concentration varies among the three YAN magnitudes (high, medium, and low) from year-to-year within many of these varieties.
Some examples include the second "Niagara 4" or "Vidal Blanc 4," which had YAN concentrations that ranged in the "high," "medium," and "low" magnitude over various harvest years. Graph 1 shows that other varieties varied between "high" and "medium" YAN numbers. The "apple" variety demonstrates great variation in its YAN in 2010 compared to previous vintage years.
This annual variation in YAN demonstrates a need to measure the nitrogen content each harvest season. The value obtained should provide the winemaker with the appropriate information for making specific nutrient additions that will benefit the fermentation best at the time of harvest.
As mentioned previously, the variation in YAN values for a given variety illustrates a need to:
- Measure YAN on an annual basis for each variety that comes into the winery.
- Stop the use of mid-range nutrient additions that would be appropriate for "medium" YAN fermentations. With such variation in YAN concentrations, it is best to determine where the must/juice lies in terms of being a "high," "medium," or "low" YAN product. Nutrient additions should adhere to supplier recommendations based on individual fermentation conditions to decrease the risk for stuck or sluggish fermentations, minimize hydrogen sulfide formation, and enhance the quality of the wine by the end of fermentation.
- Stop the excessive use of DAP. While the use of DAP has been linked to simplifying the aromatic component of a wine, the variation in YAN data highlights how DAP may not always be needed for fermentation supplementation. For example, high YAN fermentations would not typically require a DAP addition, dependent on the nutrient supplier.
- Keep accurate record books to evaluate YAN trends for a specific variety and assess if trends exist for a given vineyard or variety.
The following graphs show more YAN data on several varieties grown throughout Pennsylvania and New York. This data is included to show the variation in YAN with many wine grape varieties grown in both states.
Graph 2shows YAN data from 2006-2011 for Pinot Gris/Grigio, Riesling, Seyval, and Vignoles varieties produced in Pennsylvania or New York.
Graph 3shows YAN data from 2006-2011 for GR7, Merlot, Pinot Noir, and Sangiovese varieties produced in Pennsylvania or New York.
Graph 4shows YAN data from 2006-2011 for Chambourcin, Chancellor, Foch, Landot, Lemberger, and Leon Millot varieties produced in Pennsylvania.
Nutrients Available for Fermentation
The table below lists several different nutrient suppliers of products that contribute nitrogen during primary fermentation. This is to emphasize the variation in nutrient products and how supplier recommendations differ. Each of the brands offered by a given supplier represents a line of products to be used for different YAN conditions. Fermaid, for example, has several options available for winemakers to choose from: Fermaid K, Fermaid O, and Fermaid A. (This list is just an example for winemakers and should not replace current product information provided by the supplier.)
Table 1:Nitrogen Product Lines that Contribute to YAN during Fermentation and Optimal YAN Rates per Supplier Recommendations
|Company or Supplier||Nutrient Product Lines||High/Medium/Low YAN Rates|
|Beverage Supply Group (BSG)/The Wine Lab/Lesaffre||Superfood™ |
|Recommended YAN Levels to Reach by End of Fermentation: |
≤21°Brix: 200-250 mg/L N
23°Brix: 250-300 mg/L N
25°Brix: 300-350 mg/L N
|Enartis USA or Vinquiry||Nutriferm||High: >225 mg/L N |
Medium: 125-225 mg/L N
Low: <125 mg/L N
|Gusmer Enterprises||MicroEssentials™||Addition rates and timing based on specific fermentation conditions|
|High: >180 mg/L N |
Medium: 140-180 mg/L N
Low: 40-140 mg/L N
|Lallemand or Scott Labs||GoFerm®|
|High: >200 mg/L N |
Medium: 125-200 mg/L N
Low: <125 mg/L N
For a complete listing of all products, please see individual supplier's catalogs or websites. This list was made as complete as possible at the time of its publication.
With a better understanding of YAN and YAN management during fermentation, winemakers can take a proactive approach at controlling the fermentation and final wine quality. Improving YAN management practices offers several advantages to the winemaker:
- Minimize hydrogen sulfide occurrences in the finished wine.
- More successful, dry fermentations.
- Improve the number of clean wines by the completion of fermentation.
- Reduce the number of stuck or sluggish fermentations, which may contribute to other problems or flaws in the finished wine.
- Develop a better understanding of YAN values and nitrogen needs for wine varieties made at the winery.
- Reduce unnecessary costs for fermentation nutrients by only using those nutrients required for a healthy fermentation.