Scott Labs Yeast Nutrient Choosing Guide
Last Updated: 7/2021
Applies to: Winemakers looking for assistance in selecting and comparing Scott Labs yeast nutrients and yeast derivatives. This guide contains a downloadable pdf choosing chart that characterize our yeast nutrients and derivatives by specifications and sensory impact.Download
Selecting Yeast Nutrients for Success
Why use yeast nutrients?
Yeast require nitrogen in a form they can assimilate. Yeast assimilable nitrogen (YAN) consists of most amino acids, ammonia, and some types of peptides. Grapes vary in their YAN content. When determining the YAN content of juice/must, both assimilable amino acids (proline is not assimilable) and ammonia need to be measured. Yeast require vitamins and minerals. Interestingly, the higher the YAN the more vitamins and minerals yeast require.
Vitamins and minerals are co-factors for growth and aroma metabolism and yeast cannot survive without them. Yeast survival factors (sterols and unsaturated fatty acids) are essential for healthy plasma membranes. When yeast have sufficient survival factors, sugar uptake can continue throughout fermentation and the toxic effects of ethanol can be minimized. By providing nitrogen, vitamins, minerals, sterols and unsaturated fatty acids, the cells will be off to a great start and wine quality will be enhanced!
How Much YAN Is Required?
The amount of YAN yeast require depends on the following: individual yeast strain requirements, initial sugar content, fermentation temperature, oxygenation, turbidity, pre-fermentation practices and fruit quality. YAN will vary between vintages, vineyards and varietals so it is necessary to analyze each lot of fruit. Analysis should be conducted as close to yeast inoculation as possible.
Yeast Strain Nutrient Needs
Different yeast strains have different nitrogen demands and are classified as low, medium or high nitrogen need according to the following:
- Low nitrogen-demand: yeast need 7.5 ppm YAN per 1°Brix
- Medium nitrogen-demand: yeast need 9 ppm YAN per 1°Brix
- High nitrogen-demand: yeast need 12.5 ppm YAN per 1°Brix
Vitamins and minerals are quickly consumed (even in healthy fruit) by native microflora and other intentionally introduced yeast such as the non-Saccharomyces yeast in our portfolio. This means that prior to Saccharomyces inoculation essential factors may be deficient in musts with significant microbial activity. However, proper supplementation can compensate for these deficiencies.
The presence of molds and rot will impact grape juice/must chemistry. Studies have shown that grapes impacted by Botrytis cinerea and other molds are highly deficient in YAN and other essential nutrients.
Quality of Nitrogen
Organic (amino acids) and inorganic nitrogen (ammonia) each have a distinct role and impact on fermentation. While yeast may show an affinity for inorganic nitrogen, a yeast diet balanced with organic nitrogen can produce healthier fermentations, better aromatics (e.g., terpenes and esters) and lower levels of undesirable compounds (e.g., ethyl acetate and hydrogen sulfide).
Juice Chemistry and Conditions
- Initial sugar content: The higher the initial sugar content, the more YAN required.
- Temperature: An increase in temperature stimulates fermentation rate and yeast growth, thereby requiring increased levels of nitrogen.
- Oxygen: When adding oxygen to the juice/must, nitrogen is captured faster, therefore more nitrogen is needed.
- Turbidity: When juice is over-clarified (<50 NTU), many nutritional factors for yeast are removed, making it necessary to supplement with complete and balanced nutrients.