Understanding Yeast Nutrients
Yeast nutrients are the substances this microorganism needs to perform its various functions, primarily reproduction and fermentation. These ingredients may be naturally present in the yeast’s environment or intentionally added to the yeast culture medium in optimal quantities to ensure that its cells thrive.
The nutrients useful to yeast fall into several categories of substances: sugars, nitrogen, minerals, vitamins, amino acids, lipids, sterols, and more. The cells draw what they need from these sources to survive, multiply, and ferment… Whether the goal is to produce large quantities of yeast in industrial fermenters or to successfully ferment bread dough or beer wort, for example, it is essential to understand the nutritional needs of yeast.
What are the different types of nutrients for yeast?
Yeast cells finely tune their growth and behavior based on the available nutrients. They can modulate their growth rate in response to their nutritional environment by altering the duration of their cell cycle by a factor of at least 10.
Sugars, nitrogen, vitamins, minerals… Each type of nutrient contributes to the processes of fermentation and reproduction. By adjusting the amount of these ingredients added to the wort or fermentation medium, one can optimize fermentation activity.
Carbon Sources
Yeasts preferentially consume glucose or fructose over other mono-, di-, and trisaccharides, such as maltose, sucrose, raffinose, or trehalose, and favor any fermentable carbon source over non-fermentable ones, such as glycerol, ethanol, or acetate, which are much more complex to assimilate.
This hierarchy of sugar consumption is established through the regulation of various key enzymes involved in glycolysis and gluconeogenesis.
For example, in brewing:
- At the start of fermentation, the yeast consumes the glucose and fructose in the wort.
- When these sugars are depleted, it moves on to maltose (malt sugar), then to maltotriose (a longer-chain sugar).
- If there really is nothing left, it can recycle the ethanol produced (but this is rare, as it requires a lot of oxygen).
In the case of bread, once the sugars (glucose, fructose, sucrose) have been depleted, the yeast consumes the maltose produced by the digestion of starch via endogenous or added amylases, while producing ethanol and secondary metabolites such as glycerol and organic acids that influence the final quality of the bread.
H3: Sources of Nitrogen
Nitrogen is the nutrient that yeast needs most to build new cells, produce enzymes, and synthesize proteins.
There are various sources of nitrogen available for yeast nutrition.
- Inorganic nitrogen (or mineral nitrogen). These are ammonium salts: ammonium sulfate and diammonium phosphate (DAP). These forms are most readily assimilated by the microorganism, which has a high need for them at the start of fermentation. In winemaking, for example, mineral nitrogen enables rapid cell proliferation at the start of fermentation. It is entirely consumed during the first four or five days of fermentation1.
- Organic nitrogen. It can come from yeast autolysates, produced by the breakdown of yeast cells, and provides nitrogen in the form of amino acids. This is the cells’ second source of nitrogen, which they consume once inorganic nitrogen has been depleted. It is this organic nitrogen that is primarily responsible for the development of floral notes in wines.
Nitrogen requirements depend on the strains used and the conditions of the fermentation environment, but a deficiency can halt fermentation or cause undesirable aromatic notes.
Vitamins and Minerals
Vitamins and minerals are not directly consumed by yeast cells but are used to carry out their cellular reactions.
- Important vitamins include biotin, thiamine (vitamin B1), pantothenic acid (vitamin B5), and nicotinic acid. They play a role in reactions related to cell growth, energy production, and aroma formation. They ensure sufficient yeast growth and improve the yeast’s resistance to stress2.
- Minerals that serve as nutrient sources for yeast include magnesium, zinc, manganese, potassium, and phosphate. They help maintain cell membranes, support cell growth, enhance fermentation performance, and boost the cells’ resistance to alcohol- or heat-related stress.
A deficiency of vitamins and minerals during fermentation will slow it down, reduce the cells’ resistance to alcohol, and allow undesirable flavors to form in the final product.
How to Use Yeast Nutrients?
Various types of nutrients designed for brewing and winemaking are available on the market. They help prevent stuck fermentation and the formation of undesirable flavors. These ingredients must be added in stages, as the microorganism needs them at different points in its life cycle during fermentation3 . For most beers, it is generally sufficient to add 1 teaspoon (5 grams) of yeast nutrient per 20 liters (5 gallons) of wort4.
Solutions to Common Fermentation Problems
Proper nutrient management during the fermentation process helps ensure a complete and clean fermentation. A slow start to fermentation can be stimulated by adding a nitrogen source, while a balanced nutrient blend can prevent the production of undesirable flavors and revive a fermentation that has stalled.
Reviving a Stalled Fermentation
A stalled fermentation is one of the most common obstacles encountered in beer and mead production. A stall may be caused by a nutrient deficiency, an excessively high alcohol content, or an inappropriate temperature. Signs of a stall may include unconverted sugars and very slow yeast activity. A stalled or incomplete fermentation can be corrected by adding a specific nutrient complex containing nitrogen, minerals, vitamins, and more.
In bioethanol production, for example, the addition of micronutrients increases the microorganisms’ stress tolerance and improves yield5.
The wine industry also commonly uses controlled additions of yeast-based nutrients to improve wine quality, particularly to promote the formation of desirable aromatic compounds and reduce undesirable notes6.
Yeast-Based Nutrients Driving Innovation
Due to their composition, yeasts can also serve as nutrients in sectors involving fermentation, particularly in industrial biotechnology.
Yeast-based nutrients, such as yeast extracts, dry yeast, autolyzed yeast, and yeast peptones, are known to enhance the growth and productivity of microorganisms and animal cells. They can be used in the production of biopharmaceuticals, antibiotics, culture media for diagnostic tests, lactic acid bacteria, probiotics, bio-ingredients for human and animal feed, renewable chemicals, and biocontrol products.
In short, whether used to ensure the success of traditional fermentation or to support more innovative applications, yeast and yeast-based nutrients remain an essential tool for guiding microbial activity and ensuring higher-quality fermentations.
