Yeast Nutrition for a Successful Fermentation

September 2014 newsletter by Enartis Vinquiry

Yeast nutrition is an essential factor in the overall health and success of fermentation. Managing nutrient requirements not only allows for regular and complete fermentations but enhances sensory quality. Nitrogen, the most important yeast nutrient, is a key factor that has a significant impact on wine fermentation.


Why do yeasts need nutrients?

Nitrogen (YAN), vitamins (thiamine) and mineral salts (Mg, Zn) are essential for yeast activity. Yeast nutrition determines kinetics, completion of fermentation and impacts the organoleptic profile of wine. Additionally, sterols and long-chain fatty acids are elements that help yeast survive in stressful conditions and facilitate the completion of fermentation.

Different nutrients, different assimilation, different action:

Thiamine is a vitamin used as a co-enzyme in the alcoholic fermentation pathway. It stimulates yeast growth, speeds up fermentation and reduces production of SO2 binding compounds.

Minerals are components of the yeast cell membrane and help maintain fermentation metabolism activities.

Nitrogen is metabolized by yeast to synthetize proteins. It stimulates yeast multiplication, keeps yeast metabolism active, prevents H2S and mercaptan formation and stimulates aroma production.

Yeast Assimilable Nitrogen (YAN) is composed of ammonium ions and amino acids (except proline).

    • Ammonium ions are the favorite ‘food’ of yeast. Easy and fast to use, ammonia impacts mostly yeast growth and population.
    • Amino acids are harder to be assimilated. They represent the qualitative, healthy and delicate ‘food’ for yeast, which impacts their growth, health and efficiency through the fermentation as much as aroma production. Some amino acids can be used as aromatic precursors to synthetize esters, higher alcohols or sulfur compounds.

Sterols and unsaturated fatty acids are components of the yeast cell membrane, and are responsible for its fluidity. They maintain yeast capacity for consuming sugar, increase alcohol tolerance and reduce volatile acidity production. Oxygen has a synergistic effect with sterol production.

What happens if the nutrition is not enough?

  • A deficiency in thiamine may reduce yeast growth, slow fermentation and promote theaccumulation of pyruvic acid and acetaldehyde, components responsible for oxidation and binding SO2. The development of wild yeasts, botrytis and other grape mold infection decreases the thiamine content of must.
  • Low levels of sterols, oxygen and/or unsaturated fatty acids may shut down sugar consumption (stuck fermentation) and increase volatile acidity. Strong juice fining (turbidity <100NTU) or a lack of oxygen will increase the need to add these nutrients.
  • Without proper nutrition introduced at the right stage in their growth cycle, yeast can come under stress and produce undesirable characteristics: off-flavors (hydrogen sulfide, oxidation…), high bound SO2, stuck or sluggish fermentations…

How much YAN is needed? How to measure YAN?

To determine which nutritional supplements are needed, analyses of Brix and YAN in must are necessary. YAN (ammonia + amino acids) can be measured by colorimetric method here at Enartis Vinquiry or in your winery with Vintessential Enzymatic Kits.

The higher the sugar content, the higher the nitrogen need is. Two simple rules can help you understand the YAN need:

To ferment 1g/L of sugar, yeast need 1mg/L of YAN.
For good population growth, a minimum of 150mg/L YAN is needed.

Example: For the complete fermentation of juice at 24°Brix (240g/L of sugar), yeast need 240mg/L of YAN.

Some external conditions such as microbial contamination, botrytis or other mold infection, strong fining, etc. can heighten the needs of yeast.

Too much YAN (>350mg/L) can induce an overpopulation of yeast, which will increase stress conditions and produce undesirable characteristics such as off-flavors or stuck fermentation.

Nutrition strategy: correct nitrogen level and aroma enhancement

Yeast don’t need all the nutrients at the same time:

During the growth phase, yeast need vitamins, minerals and nitrogen. The presence of alcohol and/or ammonium ions inhibits transport of amino acids through cell membranes and reduces their consumption. To optimize their absorption and efficiency, amino acids should be added at inoculation, before ammonium ions. At this stage, yeast can assimilate amino acids to build ‘healthy’ cells which are resistant to stress conditions and produce aromas.

At 1/3 of sugar depletion, yeast start to become stressed and the assimilation of nitrogen is lower. To complete fermentation and increase their alcohol resistance, they need fast and easy nutrients to absorb (ammonium ions) and survival factors (sterols and unsaturated fatty acids) with oxygen.
In case of strong nitrogen deficiency, must needs to be corrected by an addition of ammonium ions 24- 48 hours after inoculation (after the addition of amino acids).

The nutrient additions should be split between inoculation and no later than 1/3 sugar depletion. Late nutrient additions are ineffective for yeast activity and can promote development of spoilage organisms, appearance of off-flavors and formation of biogenic amines.

How to choose the correct products?

Enartis Vinquiry has a wide range of nutrients which provide solutions for many different conditions and purposes.

Nutriferm Energy provides quickly-absorbed amino acids (absorbed during the first part of fermentation), vitamins and mineral salts necessary for proper development of yeasts. It makes yeasts stronger and more resistant to difficult conditions. It can be used during rehydration or at inoculation.

Nutriferm Arom is a nutrient rich in moderately-absorbed amino acids (absorbed at the end of growth phase) which are aromatic precursors of fermentation aromas, vitamins and mineral salts. It stimulates yeast multiplication and synthesis of fermentation aromas. Making the addition at inoculation is recommended.

Nutriferm Arom Plus contains a high content of moderately-absorbed amino acids (absorbed at end of growth phase), selected for their aromatic precursors potential, vitamins and mineral salts. It stimulates yeast multiplication, enhances fermentation aromas production and increases aromatic intensity. An addition at inoculation is recommended for ‘neutral’ varieties and/or high yield grapes to produce more aromatic wines.

Nutriferm Advance is a complex nutrient made from yeast hulls, ammonium phosphates and cellulose which provides ammonium ions, sterols and unsaturated fatty acids. It accelerates end of fermentation, exerts a detoxifying action, increases yeast alcohol resistance and prevents formation of off- aromas (H2S, mercaptans). This nutrient can be used at 1/3 of sugar depletion (no later), with oxygen for optimized effect.

DAP is pure ammonium ions produced as diammonium phosphates. It provides fast and easy-to-adsorb nitrogen. It should be added after amino acids and no later than 1/3 of sugar depletion.

 Nutriferm EnergyNutriferm AromNutriferm Arom PlusNutriferm AdvanceDAP
YAN (mg/L) for 10g/hL10-1515-2015-2015-2021
Amino acids++++++++++++++
Ammonium ions++++++++
Aromatic precursors++++++++++++++
Unsaturated fatty acids++++++++++++++++
Addition timeYeast inoculationYeast inoculationYeast inoculation1/3 sugar depletionAfter amino acids. No later than 1/3 sugar depletion

We hope that this information helps you to make informed decisions regarding fermentation, yeast nutrition management and choice of products. If you have any questions, please give us a call at (707) 838-6312.

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