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Best Practices for Hard Seltzer Fermentation

Last Updated: 6/2021

Applies to: Producers experienced in grain or fruit-based fermentation who are fermenting sugar substrates to produce alcoholic bases for hard seltzer and other ready-to-drink alcoholic beverages. This article serves as an introduction to the pdf downloads which are complete process and product recommendations for fermenting hard seltzer.

pdf Downloads

QUICK GUIDE

Printable one-page guide including yeast/dosage rates and rehydration instructions

Download

FULL GUIDE

Complete guide for hard seltzer fermentation process and product recommendations.

Download

What's so Hard about Hard Seltzer?

Hard seltzer and other ready‐to‐drink blends of carbonated water, alcohol, and flavoring are popular with consumers looking for low calorie, low carbohydrate, gluten‐free alcoholic beverages. Several challenges need to be addressed to produce fully fermented bases in a reasonable time frame from low nutrient sugar substrates. Without intervention, sugar fermentations are notoriously slow, unpredictable, and differ significantly from malt-, fruit-, or grape-based fermentations.

NUTRIENTS ARE IMPORTANT

Yeast require a balance of vitamins, minerals, survival factors and nitrogen in addition to an energy (sugar) source to properly grow and survive during fermentation. Malt- and fruit-based ferments typically have ample amounts of nutrients, but sugar-based ferments are nutrient deserts and supplementation is essential. Nutrients decrease fermentation time and promote complete (dry) ferments.

NOT ALL NUTRIENTS ARE THE SAME

Nitrogen is one of the most important yeast nutrients. Yeast use assimilable nitrogen to synthesize cellular proteins, enzymes, and nucleic acids. Without adequate nitrogen, fermentation slows because yeast cannot maintain their cell function or reproduce.

We advocate using two types of nutrients for seltzer ferments: GO-FERM PROTECT EVOLUTIONTM used during dried yeast rehydration and NUTRI2TM added at the start of fermentation. GO-FERM PROTECT EVOLUTION is a cell protectant that provides natural micronutrients and survival factors directly to the yeast during rehydration. NUTRI2 is a complex yeast nutrient that delivers 100% natural organic nitrogen in the form of highly assimilable amino acids for growth and survival during fermentation.

Inorganic nitrogen sources, such as diammonium phosphate (DAP) or urea, can be used to overcome some nitrogen deficiencies. However, these chemicals cannot be used in organic-labelled seltzers and, in the case of urea, there is a high risk of ethyl carbamate formation, a compound classified by the FDA as a probable carcinogen.

Note: Nitrogen supplementation recommendations for malt-, fruit-, and grape based fermentations are based on targeting a certain Yeast Assimilable Nitrogen (YAN) or Free Amino Nitrogen (FAN) content. However, when YAN/FAN targets developed for malt-, fruit-, and grape based fermentations are used for calculating nitrogen supplementation for low nutrient sugar ferments, satisfactory fermentation outcomes are rarely achieved. We have found that a more complex nutrition strategy is necessary to achieve good results and that YAN/FAN availability is only part of that strategy.

YEAST STRAIN & DOSAGE MATTERS

Adequate yeast dosage produces better results and higher gravities require higher dosage rates.

High gravity seltzers are especially difficult to ferment due to increased osmotic pressure from high sugar at the start of fermentation and elevated alcohol at the end of fermentation. Even with nutrient supplementation, sugar ferments struggle when dosage rates are too low.

Strain kinetics and sensory impact determine suitability for seltzer.

Yeast strains vary in alcohol tolerance, nutrient requirement, temperature tolerance, ability to breakdown disaccharides, fermentation speed, and many other traits. Many strains are not robust enough to ferment seltzer bases. Therefore, VI-A-DRY BOSS™ yeast is recommended for its strong fermentation kinetics, low nutrient needs, neutral sensory effects, and ability to breakdown sucrose and other sugars.

SUGAR SOURCE MATTERS

Sugar source can affect fermentation rate and monosaccharide sugars may be faster to ferment.

Common sugar sources used for seltzer fermentation include:

  • Sucrose (table sugar/cane sugar) – disaccharide of glucose and fructose
  • Dextrose – glucose derived from corn
  • Invert sugar – mixture of glucose and fructose made by sucrose hydrolysis
  • Agave – sugar from the agave plant consisting primarily of fructose
  • Maltose – disaccharide of two glucose

Yeast are only able to utilize monosaccharide (single unit) sugars of glucose and fructose. For yeast to use disaccharides (sucrose, maltose, etc.) the sugar must first be broken down into monosaccharide units. Yeast’s ability to break down di- and trisaccharides into useable glucose and fructose varies and is strain dependent. Most yeast can break down sucrose into glucose and fructose by producing invertase. However, in difficult fermentation conditions, the additional yeast energy required to produce invertase may slow fermentation. Other sugar and yeast strain combinations may not be compatible and enzyme additions may be necessary to break down larger sugar molecules into glucose and fructose.

FERMENTATION TEMPERATURE MATTERS

Identifying optimal fermentation temperature can be tricky.

Temperature affects fermentation rate, yeast health, and sensory impact. Despite its importance, the numerous factors affecting low-nutrient sugar fermentations make it difficult to provide clear temperature guidelines. Yeast strains vary in their temperature tolerance and can be stressed when fermenting at the upper or lower end of their recommended temperature range, especially as alcohol increases. Though fermentation is faster at warmer temperatures, the risk of yeast stress leading to stuck ferments and off-odors also increases. Finding a fermentation temperature that balances fermentation speed and yeast health will likely require experimentation for any given process.

DOES PH DURING FERMENTATION MATTER?

Sudden drops in pH during fermentation have been known to cause yeast stress and could be an issue depending on many factors (nutrition regimen, water chemistry, etc.). In trials with our recommended products, we found fermentation is unaffected by decreases in pH. If you are experiencing fermentation difficulties following other protocols, pH may be an issue and using a buffer such as potassium bicarbonate may be useful.

pdf Downloads

QUICK GUIDE

Printable one-page guide including yeast/dosage rates and rehydration instructions

Download

FULL GUIDE

Complete guide for hard seltzer fermentation process and product recommendations.

Download