Brewers go to great lengths to ensure yeast remain healthy, viable and perform optimally during fermentation. Brewing yeast nutrients can further minimise the risk of any problematic fermentations by providing the essential nutrients yeast need to stay in peak condition. But what if the yeast nutrients also enhance the aroma profile of the beer and boost flavour? And what if you can choose the aromas, you want enhanced? Andrés Furukawa, Brewing Technologist at the AEB Group, explains all.

Yeast nutrients will ensure a healthy fermentation, meaning that, the yeast has what it needs to perform at its absolute best and in doing so deliver the results you want. They can guard against poor fermentations and off flavour formation.

Many brewers will often use yeast nutrients as a matter of course – a better-safe-than-sorry measure – which is perfectly fine. Afterall, a yeast nutrient is considered a natural product. They are essentially yeast hulls and autolysates of yeast, and contain diammonium phosphate (inorganic nitrogen), vitamins and minerals. 

In peak condition yeast provide consistent, reliable fermentations and create rich complex aromas and flavours. However, nutrient deficient wort or one in which the nutrients have limited bioavailability for the yeast cells, can create a sub-optimal environment for the yeast. 

This is compounded by the presence of alcohol and carbon dioxide, and a less than ideal wort pH. These factors lead to yeast stress causing stuck (or slow) fermentations, inconsistent attenuation rates, off-flavour formation, and reduced yeast cell viability. High gravity worts (high alcohol fermentations) or high adjunct fermentations can also be challenging. Particular attention needs to be given to how yeast is propagated, the re-pitching rates, how, when, and where active dry yeast and yeast nutrients are added, and the temperature control during fermentation.

Aroma boosting

At AEB we know that in wine production yeast nutrition is of vital importance not only for ‘healthy’ fermentations but also for aroma and flavour development. Yeast nutrition plays a key role in supporting the biosynthesis of aroma-active compounds, known as thiols, during fermentation. Thiols are organosulphur compounds, also called mercaptans. Aroma- and flavour-active thiols, long known for their sensory impact in wine, have been identified only relatively recently in beer.

When created/released they give intense floral, fruity, and tropical aromas and flavours. These highly volatile aroma-active compounds are becoming more relevant, especially in craft brewing, as consumer demand for tropical aromas in hop-forward beer styles, such as West Coast and New England IPAs and modern lagers, continues to rise. 

Taking lessons from wine

Originally identified in wine, three potent thiols are known to give tropical fruit-like aromas to beer. Briefly, these are: 4MMP (blackcurrant-like), 3MH (grapefruit and gooseberry-like) and 3MHA (passionfruit and guava-like). They exist in free and bound form in hops, often variety-linked; and to a lesser extent in malted cereals such as barley and wheat. Their release is linked to a yeast gene (IRC7) which encodes an enzyme responsible for cleaving thiol precursors and their biotransformation into aroma-active forms.

Wines made from Sauvignon grapes are rich in aroma-active thiols, yet the grape itself has predominantly the bound forms; prompting brewers to add Sauvignon grape skins to the mash rather than late hop. In contrast to wine yeast, most brewing strains lack the gene, which has led to the development of ‘thiolised’ yeasts using gene editing. Yeast strains have also been altered with GM or hybridisation techniques to promote thiol expression in beer.

So much more than just a yeast nutrient

Building on our extensive knowledge of aroma-active compounds in wine, we’ve been collaborating with brewers to enhance beer aroma and flavour, sustainably (and more naturally), through the complex interactions of yeast nutrition including amino acid composition, wort composition, pH in wort fermentations, point of application, and hop variety. The aim being to reduce high hopping rates, negate the use of grape-skin based aroma boosting products, and avoid the use of GM yeast.

The yeast nutrients we’ve developed for winemaking can enhance a brewing yeast’s ability to convert malt- and hop-derived aroma-active thiol precursors, and other relevant fermentation flavour active by-products, such as esters, terpenes, and higher alcohols, via the process of biotransformation, to release intense and pleasant floral or fruity aromas in beer. 

There’s no doubting the appeal of designing and creating beers with distinct aroma profiles using yeast nutrients. And for low and no alcohol beer that appeal is even greater.

About the author: Andrés Furukawa is Brewing Technologist at the AEB Group. He has a keen interest in wine yeast and yeast nutrition for beer brewing and for creating and enhancing aroma and flavour. Andrés is also the founder and head brewer at Macken Bryggeri in Sweden, and brewmaster at Nils Oscar Brewery.

What’s in a yeast nutrient?

The main nutrients yeast need are carbohydrates, in the form of glucose, fructose, maltose, maltotriose, various amino acids and other nitrogen containing compounds collectively known as Free Amino Nitrogen (FAN), vitamins (biotin, pantothenic acid, thiamine, inositol), and minerals (zinc, phosphate, potassium, calcium, magnesium). 

A typical yeast nutrient contains:

• Amino acids – although yeast make their own amino acids, some are taken in from the wort
• Phosphate – or diammonium phosphate (DAP) is a water-soluble salt that delivers valuable nitrogen
• Vitamins & minerals – including thiamine (vitamin B1), pantothenic acid (vitamin B5), biotin (vitamin B7), inositol (B8), ascorbic acid (vitamin C) and essential minerals (zinc, manganese, sodium, potassium, calcium, and magnesium). All necessary for the metabolic reactions yeast need to do their job. They function as catalysts during fermentation and protect yeast cell walls and support flocculation. 
• Yeast hulls – these are water-insoluble inactivated yeast cells. Live yeast feed off the nutrients they contain.