Using Yeast Nutrients
TroubleShooting
Josh Given • Grand Rapids, Michigan asks,
I want to know more about yeast nutrients. The “Oak It Up” article in the September-October 2024 issue is a great example of why nutrients are a bit of a mystery to me; some of the recipes call for nutrients and others don’t. What are some of the different nutrients used by homebrewers and when should I be using them?
This is a great question. Before digging into details, you make an interesting observation about the “Oak It Up” article. On the surface, a brewer may assume that recipes calling for nutrients may be big beers, beers with relatively high levels of adjuncts, or hybrid styles like oenobeers (which are part beer, part wine). In the case of the four recipes in “Oak It Up,” which are clone recipes that came directly from the brewers, it looks like there is another trend; some brewers note nutrients in recipes and others do not. Whether a recipe calls for nutrients or not, there are reasons why some brewers always add a nutrient to wort before fermentation.
Zinc is the primary nutrient usually deficient from wort, even in all-malt brewing. Kunze writes in Technology Brewing & Malting that “zinc is of greatest physiological importance for protein synthesis and for cell growth of yeast and thus for fermentation. If there is a zinc deficiency yeast growth is retarded, the fermentation proceeds slowly, and there is incomplete reduction of diacetyl. It is therefore advantageous to retain the zinc present in malt as much as possible. However, only about 20% of the zinc in the malt goes in the solution on mashing in and the zinc content then decreases further during the course of mashing.”
There are three common forms of zinc that brewers add to wort: Dry zinc sulfate or zinc chloride, stock solutions of zinc sulfate or zinc chloride, and zinc-enriched yeast products like Servomyces. Because about 50% of zinc added during wort boiling is lost with trub, many brewers add zinc to the fermenter with their pitching yeast. Big shout out to Mitch Steele for providing input about typical zinc losses experienced in commercial breweries. The target dosing rate of zinc is low, typically 0.2 to 0.3 mg/L, and should be accurately dosed as zinc is toxic to yeast when the levels are too high. Note that zinc additions will vary depending on if added in the kettle or fermenter.
The most common zinc salt used in brewing is zinc sulfate heptahydrate and the required dosage for the typical 5-gallon (19-L) batch of homebrew is a whopping 0.02 grams; far too small of a dose to accurately measure at home. A common remedy to this challenge is to make up a weak solution and to dose based on volume, making the addition easier to properly control. When dosing a 2.5% solution (25 g/L) into the typical homebrew batch, 0.7 mL is all that is needed; still a small dose, but easy to measure with a pipette.
Servomyces is another convenient way to add zinc to wort. Like many biologically produced products used in German brewing, Servomyces allows German brewers to be Reinheitsgebot-compliant and to deliver the yeast dose that helps fermentation (direct addition of zinc from zinc sulfate and zinc chloride is not permitted by the Reinheitsgebot). Servomyces is made by growing yeast cells in an enriched media. Zinc and other trace minerals are brought into the cell, the cells are dried, packaged like other dried yeast, and added to the wort during the last 10 minutes of the boil to kill the yeast cells. Typical dosage is 10 mg/L, or 0.2 grams per 5-gallon (19-L) batch; this is doable for small-scale batches but does require a digital scale with 0.01-gram resolution.
The key takeaway about zinc is that it typically increases fermentation rate, reduces the chance of stuck or lagging fermentations, results in healthier daughter cells, improves harvested yeast quality, speeds diacetyl reduction, and improves yeast flocculation. The combined effect of these positive effects is better-tasting beer. When accurately dosed, adding zinc to wort is a no-brainer.
Low-protein and protein-free adjuncts like rice, corn, and sugar dilute wort amino acid levels. Because yeast require a source of nitrogen for cell growth, nitrogen-deficient worts can be problematic, especially in high-adjunct and/or high-gravity brews. Brewers use the FAN, or free amino nitrogen, metric as an indicator of wort amino acid content. Unfortunately, this method measures compounds like proline, small polypeptides, and protein, which have no nutritional value to brewing yeast. Winemakers, on the other hand, use the YAN, or yeast assimilable nitrogen, metric to directly measure amino acids that yeast can use. In any case, zinc additions do not address nitrogen deficiencies in wort, but nitrogen-containing nutrients do.
Yeast cells can use nitrogen from amino acids, commonly called organic nitrogen in nutrient jargon, or from inorganic nitrogen sources like urea and diammonium phosphate (DAP) to synthesize amino acids and proteins required for cell growth. Inorganic sources of nitrogen are quickly used by yeast during the growth stage of fermentation and can lead to very fast ferments that sometimes generate more heat than fermenter cooling systems — especially air-cooled carboys, buckets, and plastic fermenters — can remove. Because hot fermentations and excessive yeast growth can lead to flavor problems and reduce ethanol yield, yeast nutrients often contain a blend of organic and inorganic nitrogen with or without zinc.
Although brewers can use zinc-free wine nutrients for brewing, nutrient blends produced for brewing applications always contain zinc. Wine nutrient blends, however, do not contain zinc because zinc is not a TTB-approved nutrient, though there have been petitions to permit its use for wine. The practical point is to read labels to better understand what is being added because all beers benefit from zinc. Blends containing DAP, yeast extract/yeast hulls/yeast cells, and minerals translate to blends with inorganic nitrogen, organic nitrogen, and zinc, plus some other bits and bobs.
Determining the dosage of complex nutrient blends is a challenge for all brewers who do not measure FAN or YAN in wort. The good news is that brewing nutrients are typically targeted to two general types of wort: High-adjunct and moderate-to-no-adjunct worts. And the suggested dosing rate of complex brewing nutrients is based on zinc dosage. For example, the suggested dosage rate of Yeastex 82, a common nutrient used for moderate-to-no adjunct-brewing, is 40 mg/L, and the dosage rate of Yeastex 61, a common nutrient used for high-adjunct brewing, is 70 mg/L. Both nutrient blends deliver similar levels of zinc to wort, but Yeastex 61 supplies more nitrogen.
One of the advantages of using complex nutrient blends is the higher dosing rate, making measurement much easier for small-scale brewing. For example, adding 0.8 grams/5-gallon (19-L) batch of Yeastex 82 is easy to measure and provides zinc, other trace elements like manganese, B-vitamins, and nitrogen to wort. There are many brewing nutrient blends on the market with similar dosage rates. The key benefits to nutrient blends are their ease of use and broad-spectrum composition. A potential downside, however, is adding components to your wort that may not be needed.
No discussion about current brewing trends and nutrients is complete without touching on two beverage types: Big-ass beers (BABs) and seltzers. Both beverage types present challenges to producers and the yeast cells enlisted to do the heavy lifting. Although BABs typically contain a boatload of FAN and seltzers typically contain zero without nutrients, both are made possible through the proper use of nutrients. One nutrient use strategy borrowed from winemakers is to add nutrients in stages. For very high starting gravities, nutrients may be added two to three times over the course of fermentation to keep things moving towards the finish line without overloading yeast cells with too much nitrogen at any given time. Some nutrient blends, like Bevie’s Pathfinder N-Pure, are designed for one addition along with the pitching yeast. This is a deep topic worth diving into if these types of ferments are your jam. Hopefully this sheds some light on the fascinating and diverse world of yeast nutrients.