Yeast Nutrition: Feed your yeast to ensure success

Every year, or month even, there seems to be a new trend in the brewing industry. Ranging from high-gravity fermentations to low-nutrient-available beverages; i.e. hard seltzers, hard kombucha, etc. The ideas keep on coming without a stop in sight. Whether you like or dislike these beverages is a separate discussion. What we need to focus on is that with whatever you’re brewing, a strong understanding of yeast and nutrients is a necessity. Yesterday it was this, tomorrow it’s that. But today is always a good day to learn about nutrients.

Before we jump right in, let’s take a step back and start with the main ingredient here: Yeast. I may be a little biased as I work at a major yeast company, but I have to say it — yeast is the soul of beer. They’re awesome and complex. They give our beers flavor, depth, mouthfeel, and the most important, alcohol. So let’s get a better understanding of these cool little critters. Brewer’s yeast is a fungus that falls under the genus of Saccharomyces, which literally means “sugar fungus.”¹ In the most simple of terms, yeast utilize carbon sources to produce ethanol and CO₂. There are hundreds of other reactions that occur in a yeast cell, and each reaction can be influenced by different factors: pH, pressure, temperature, wort composition, etc. If you change one factor, you will likely cause a chain reaction. Yeast nutrients, also known as yeast foods, can be one component of influence. Yeast nutrition “refers to how the cells utilize food sources for subsequent anabolic and catabolic reactions that insure the growth and survival of that cell.”² If yeast are nutritionally deprived, unfinished fermentations may follow, and lead to beer off-flavors. Adding nutrients, can “improve alcohol yield, reduce fermentation time, enhance yeast viability and vitality, and increase diacetyl removal, as well as control undesirable flavor compounds.”³

Ideally, all-malt wort should provide the necessary components for a successful fermentation: Sugars, amino acids, vitamins, and minerals. However, we don’t always have the most ideal situations or ingredients; e.g. low-quality malt or a zinc deficiency. Fermentation in general is already pretty taxing on the yeast cells. With high-gravity brewing, high-adjunct brewing, sour wort, serial repitching, etc., yeast are now put into more stressful environments and need all the help they can get. Yeast nutrients are available to supplement where the ingredients fall short and can be used as a yeast “insurance” to continually have consistent fermentations.
So what do yeast need and how are these available?

Carbon: Although not an added yeast nutrient per se, I mention carbon because it’s the core component of carbohydrates — an essential component in yeast metabolism. Carbohydrates can be provided through sugar additions, but typically come from malt as maltose, maltotriose, and small amounts of sucrose, glucose, and fructose.1 Sugar uptake can be strain-dependent. For example, there are strains that do not assimilate the trisaccharide, maltotriose. Most brewer’s yeast are not able to hydrolyze dextrins (long-chain sugars) into fermentable sugars, but some strains, such as Saccharomyces cerevisiae var. diastaticus, produce enzymes that can. When brewer’s yeast break down and assimilate sugars, they go into glycolysis, on their way to produce alcohol.

Oxygen: Oxygen is another essential component in yeast metabolism that is typically injected separately, but still important to mention. Oxygen/air is necessary for efficient cell division immediately after yeast pitch to ensure adequate cell population for fermentation.* The oxygen is used for the production of sterols and unsaturated fatty acids, which are important in maintaining membrane structure and integrity and synthesizing healthy membranes as cells divide. These sterols and unsaturated fatty acids act like stress protectants to the yeast cell — they reinforce the membrane to uphold yeast function and viability. On the other hand, oxygen deficiency can result in poor fermentation and a high amount of acetyl coenzyme A, which can lead to increased levels of esters. This further influences the overall flavor of beer.¹
*Oxygen/air is not normally required for standard fermentations using active dry yeast on first pitch, because when dry yeast is produced, it’s in presence of copious amounts of oxygen and is therefore filled with sterols.

Nitrogen: Nitrogen is present in proteins, peptides, amino acids, and ammonium. When discussing yeast nutrients, you’ll commonly hear the term free amino nitrogen (FAN). But what does FAN mean? Free amino nitrogen is an overall measurement of the available amino acids and small peptides in wort. FAN plus ammonia ions, gives us YAN (yeast assimilable nitrogen). YAN is commonly used in the wine industry, so we will stick with discussing only FAN for simplification. Nitrogen is necessary for successful fermentations as it’s transported into the cell and integrated into key proteins responsible for yeast cell function. These proteins can affect yeast performance and beer flavor. The majority of these compounds are provided through malted barley. The malting process has been perfected over years to deliver the necessary amounts of carbohydrates, nitrogen, and enzymes for the brewing mashing process. Roughly 70% of wort FAN is produced during malting.⁴ When brewing with all-malt, the addition of a nitrogen nutrient is not necessarily required. However, if adjuncts are added to the mash, this can dilute the amount of nitrogen in the wort and an external source of nitrogen would be beneficial for the fermentation. Nitrogen can be introduced in the form of a yeast extract/autolyzed yeast (an inactivated yeast) or by inorganic compounds such as diammonium phosphate (DAP). Hard seltzer production is an extreme example of a nitrogen-deficient fermentation that is in major need of nitrogen supplementation. The minimum necessary FAN levels for successful fermentations is roughly 140 mg/L.

Vitamins: Vitamins are necessary for overall yeast health. Biotin, pantothenic acid, and thiamine are critical for enzyme function and yeast growth. These act as co-factors for the enzymatic reactions . . . in other words they help hold the 3-D structure of the enzyme in its proper shape to allow them to be most effective. Biotin is known to be one of the more crucial vitamins because it’s a catalyst for multiple important reactions, such as “amino acid metabolism, fatty acid biosynthesis, and energy metabolism.”⁵ In general, yeast cells are not capable of synthesizing biotin, so it’s derived primarily from the malt and hops used in the brewing process.⁶ These can also be added externally by common nutrient blends on the market.

Minerals: Phosphate, potassium, calcium, magnesium, and especially zinc, are crucial minerals for successful fermentations. Overall, these are needed in trace amounts, but are cofactors for enzymatic reactions such as glycolysis or alcohol synthesis. Zinc is the important mineral to note because it can be deficient even in all-malt wort due to the loss of zinc during lautering. It’s needed in the last step of fermentation. Zinc deficiencies can cause fermentation and flocculation problems. Adequate zinc in wort (0.15–0.3 mg zinc/L) positively influences the uptake of maltose and maltotriose, contributes to protein synthesis and yeast growth, protects enzymes, and stabilizes the protein and membrane systems, which in turn can provide faster fermentations and better flocculation.⁷ The common ways to add zinc to wort is by adding zinc sulfate, nutrient blends that contain zinc, or by adding zinc-enriched yeast.

Now that we have an understanding of these important nutrients, let’s go over some data that shows the benefits. A study focusing on yeast nutrients was completed by Sylvie Van Zandycke and Tobias Fischborn from Lallemand. They published a paper called The Impact of Yeast Nutrients on Fermentation Performance and Beer Quality.³ In it they took a look at 4–5 different nutrients and examined the effects of these nutrients over eight generations from 100% malt wort and high-gravity wort (60% malt/40% adjunct).

Below are Figure 1 and Figure 2 showing the fermentation kinetics in 100% malt wort among four yeast nutrients (ZnSO₄ [mineral zinc], zinc-enriched yeast, nutrient blend 1, and nutrient blend 2) on the first and eighth generation. Nutrient blend 1 and nutrient blend 2 are different brands that contain nitrogen and zinc blends with added vitamins as well. As stated before, ideally, all-malt wort does not necessarily need added nutrients. From Figure 1, you’ll notice that the control performed similarly to the nutrient-added fermentations. The differences are more noticeable as the generations go on (Fig. 2) — the two nutrient blends and the zinc-enriched yeast create faster and more consistent fermentation than the control alone.

Next they looked at fermentation kinetics in high-gravity wort containing 60% malt and 40% adjunct. The following figures show the first generation (Fig. 3) versus eighth generation (Fig. 4) yeast, using five different yeast food formulations (mineral zinc, zinc-enriched yeast, nutrient blend 1, nutrient blend 2, and nitrogen blend). This time there is a difference in the control vs. nutrients in the first generation of high-gravity brewing (Fig. 3). By the eighth generation, it is quite clear the benefits of the addition of nutrients (Fig. 4). This may be more important at the commercial level (in order to free up fermentation space) then at the homebrew level, but yeast performance is an indication of yeast health.

Please note that these tests were run in a lab setting and may not represent true brewing conditions, as stress was induced to demonstrate effect of the nutrients to show the efficiency. Also of note, the time scales of the graphs have been adjusted to make it easier to see the differences between the nutrient additions and the control.

It can be overwhelming and confusing when trying to figure out what nutrients are needed for a particular fermentation. Nutrient requirements can vary depending on one’s needs. If you don’t know where to start, ask yourself: What yeast strain are you using? Are you planning to ferment a high-gravity wort? Are you looking for more consistent fermentations batch-to-batch when re-pitching? It’s best to have an understanding of your overall goals before you start looking at all the nutrient options. If there are any questions or concerns, it’s recommended to reach out to your yeast or
nutrient supplier.

In summary, it is possible to have successful fermentations with or without added nutrients. However, for best results in high-gravity brewing or the need of consistent fermentations, nutrients are an obvious choice. Yeast are living cells and we control the environment we provide them. Give them their ideal environment, and they’ll do their job well for you.

References

¹ Lewis, M. Young, T. (2002) Brewing: Second Addition. Kluwer Academic/Plenum Publishers. 319-338.
² Just, J.; Hall, N. (Feb 2020) Fermentation Strategies for Hard Seltzer, Kombucha, and other Whacko Low Nutrient Sugar-Based Ferments. [ppt]. MBAA NorCal Technical Conference.
³ Van Zandycke, S.M.. Fischborn, T. (2008) The Impact of Yeast Nutrients on Fermentation Performance and Beer Quality. MBAA TQ 45, 290–293.
⁴ Burger, W.C.; Schroeder, R.L. (1976) Factors contributing to wort nitrogen. I. Contributions of malting and mashing, and effect of malting time. Journal of the American Society of Brewing Chemists 34, 133–137.
⁵ Wu H, Ito K, Shimoi H. (2005) Identification and characterization of a novel biotin biosynthesis gene in Saccharomyces cerevisiae. Applied Environmental Microbiology 71(11): 6845–6855. https://doi:10.1128/AEM.71.11.6845-6855.2005
⁶ Lynes, K.J. and Norms, F.W. (1948) Biotin In The Materials and Process of Brewing. Journal of the Institute of Brewing, 54: 150–157. https://doi:10.1002/j.2050-0416.1948.tb01369.x
7 Fischborn, T. et al. (2004) Servomyces: A biological nutrient. MBAA TQ. 41, 366–379.

Written by Brittney Christianson