By: Denise M. Gardner
Based on the number of questions I have received this year about yeast assimilable nitrogen (YAN), it looks like more winemakers are taking it upon themselves to measure YAN on pre-harvested fruit or on incoming juice. This can be a great step in improving wine quality! Measuring YAN offers several benefits to winemakers, including:
- Minimizing the incidence of hydrogen sulfide development in the wine.
- Enhancing varietal character by producing cleaner wines with adequate and specific nitrogen supplementation throughout primary fermentation.
- Minimizing excessive nutrient supplementations, in which left-over nitrogen (after primary fermentation) may act as nutrient sources for spoilage yeast and bacteria.
- Reducing unnecessary work for your employees by minimizing problematic production situations (e., fixing wines with hydrogen sulfide). Such actions could have economic benefit (i.e., reduction in supplies, reduction in time/labor)
Below is a quick refresher for those that may have questions about YAN.
- YAN = Ammonia Concentration + Primary Amino Acid Concentration given in the units: mg N/L (read: milligrams of nitrogen per liter)
- Most suppliers (g., Lallemand, Scott Labs, Enartis, Laffort) will providerecommendations on what to add in low, medium, or high YAN situations. Make sure you consult your handbooks or supplier websites for their product-specific recommendations.
- At the start of fermentation, you want to avoid adding diammonium phosphate (DAP) or complex nutrient additions that contain DAP (g.,Fermaid K) when hydrating your yeast. Use hydration-specific products like GoFerm or Nutriferm Energy.
- Most suppliers recommend making 2 additional nitrogen supplementation additions during primary fermentation and after inoculation. If only making 1 nutrient addition after inoculation is practical for you, add your nitrogen supplement at about 1/3 of the way through primary fermentation (e., 1/3 drop in sugar depletion).
Yeast hydration nutrients are an important component of re-hydrating freeze dried yeast. Winemakers should make sure to avoid DAP additions at this stage. Inoculation photo by Denise M. Gardner
A Review: Why to not add DAP at yeast hydration/inoculation
YAN is composed of inorganic (ammonium ion) and organic (primary amino acid) nitrogen components. Amino acids are brought into the yeast cell through transport across the cell membrane. The presence of alcohol and ammonium ions (i.e., DAP) inhibit amino acids from being brought into the cell. This is why winemakers are advised NOT to add DAP at inoculation or at the beginning of fermentation, as yeast can actively absorb organic nitrogen in the juice (aqueous) environment.
Once alcohol concentrations begin to increase, as a result of primary fermentation progression, transport of amino acids from the wine into the yeast cell will be inhibited. Therefore, the primary source of nitrogen will then come from inorganic sources, such as DAP. A more thorough summary of how nitrogen is utilized by yeast can be found at the following pages:
- Wine Made Easy Nutrient Management Fact Sheet
- Cornell University’s FAQs Associated with YAN
- YAN Data Review Over 6 Vintages
- Variations in YAN in the same vineyard sites across multiple vintage years
In general, winemakers can select from three different kinds of nitrogen-based products to add during fermentation:
- Hydration Nutrients (g., GoFerm, Nutriferm Arom, etc.)
- Complex Nutrients (g., Fermaid K, Nutiferm Advance, Superfood, etc.)
- Diammonium Phosphate or DAP
Need more direction on when to add which nutrients? Look no further! We have a practical fact sheet waiting for you at the Penn State Extension website. As a general rule of thumb, remember to make your YAN additions based on the volume of wine that you are treating. For whites, roses, and some reds (e.g., hot pressed Concords), YAN additions will be made based on the juice volume. For most other reds, YAN additions should be based on the must volume.
Dealing with Low YAN Fermentations
Low YAN fermentations are defined as having less than 125 mg N/L in the must/juice at the start of fermentation. In these situations, it’s essential for the winemaker to provide enough “food” for all of the yeast during primary fermentation.
Depending on the reference, most scientific literature will recommend adding up to 200 – 250 mg N/L. This concentration of nitrogen should provide adequate supplementation for the entire biomass throughout the duration of fermentation.
Be aware that if you are using a HIGH NITROGEN DEMANDING YEASTstrain (e.g., BM45, ICV-GRE, among others), however, you may be required to add additional supplementation. If you are starting with a low YAN situation and would like to use a high nitrogen requiring yeast strain, we recommend contacting your supplier for specific nutrient addition instructions.
Dealing with High YAN Fermentations
Many suppliers define a high YAN fermentation anywhere above 250 mg N/L. However, some YANs from Pennsylvania grown grapes are at concentrations greater than 400 mg N/L! This YAN concentration can create a challenging fermentation and processing situation for the winemaker.
Due to the excess amount of available nutrients in these situations, yeast can grow and reproduce quickly, which often leads to very rapid and hot fermentations. The speed and temperature of fermentation can affect the aromatics and quality of the wine (i.e., fast fermentations often lead tosimpler aroma and flavor profiles). This may not be an issue with some fermentations, but for many white, rosé, or fruit (other than grapes)-based fermentations, aromatic retention should be a priority by the winemaker.
Higher concentrations of the inorganic component of YAN can lead to a high initial biomass of yeast. This is a problem because the rapid increase in yeast populations can lead to starvation by the majority of the yeast by mid- to late-fermentation, especially if there is not enough nutrition to fulfill all of the yeast during fermentation. Yeast starvation leads to yeast stress, and one of the stress responses by yeast is the production and release of hydrogen sulfide. Therefore, having a high YAN at the start of fermentation may cause hydrogen sulfide issues in the wine by the time fermentation is complete.
What should you do if you have a high YAN?
- First, always reference your supplier recommendations. Each year, suppliers publish current guidelines for how and when to add various nutrients during fermentation.
- I’ve found it helpful to document trends in high YAN fermentations. For example, if you notice that a variety with a routine high YAN year-to-year, note the years where hydrogen sulfide becomes an issue. Good record keeping during primary fermentation can remind you what you did during production. You may need to alter these practices for the following vintage year.
- If all else fails, refer to Penn State’s Wine Made Easy Fact Sheet on Nutrient Supplementation during Primary Fermentation
Additionally, high YAN concentrations may leave some nitrogen left over by the end of fermentation and could remain in suspension in the finished wine. This excess “food” could be available for other microorganisms (like acetic acid bacteria or Brettanomyces), which could potentially lead to spoilage problems if the wine is not properly stabilized. In high YAN situations, it is especially important to ensure that the wine is stabilized with adequate sulfur dioxide additions and by minimizing other risk factors (e.g.,temperature control of the wine).
It is also be researched that high starting YAN values may led to increased concentrations of ethyl carbamate. Ethyl carbamate is naturally produced by fermentation, but it is a mild carcinogenic compound. For this reason, many countries have legal maximum ethyl carbamate concentrations in wine. For more information on ethyl carbamate, please see this guide published by UC Davis or this Extension report from Virginia Tech’s Enology Grape Chemistry Group.
Our Understanding of YAN is still Developing
Every year, YAN is a big topic of conversation amongst industry suppliers and academics. Current investigations include:
- The impact of primary amino acid uptake as a function of temperature, reported by Cornell University and discussed at the 2016 American Society of Enology and Viticulture (ASEV) – Eastern Section conference (Missouri) in a presentation by Scott Labs.
- YAN recommendations for hybrid varieties produced in the Mid-Atlantic, a topic discussed by Dr. Amanda Stewart from Virginia Tech University during the 2014 PA Wine Marketing & Research Board Symposium. This includes looking at other nutritional factors beyond nitrogen supplementation, which was also discussed at the ASEV-Eastern Conference in 2016 by Scott Labs.
- Optimal nutritional strategies for challenging fermentations, which is often reported in supplier catalogs like the Scott Labs 2016 Handbook