By Eric Dixon and Sylvie Van Zandycke, Lallemand Brewing

Brewers are always looking for ways to make consistent and flavorful beer. The ever-changing state of the world these days presents newer challenges to producing beer, gathering raw materials, and distributing a finished product; using dried yeast can be a small step with considerable benefits throughout the brewing operation.

Stability, versatility, and consistency are just a few attributes that make dried yeast a dream come true for any brewing setting.

In recent years, many advancements in the industry have helped to elevate dried yeast to the Premium product it is today. A better understanding of brewing yeast’s nature, its ability to be dried while maximizing viability were key towards achieving the quality product the brewers were waiting for.

The Relevance of the Drying Process for Yeast Health

Before we talk about some of the things that make dried yeast beneficial, let’s talk about how it’s made (Figure 1).

Production can be a very stressful process for the yeast. Growing cells starts in a lab where they are moved to large scale production using filtered air and a sugar source as food.

As a yeast producer, the challenge is to work with 100% sterile material to keep the culture as pure as possible during its propagation process from the yeast inoculation slant (stored in the culture collection in liquid nitrogen -196°C to preserve genetic integrity) until the end of the process.

Saccharomyces cerevisiae has the potential to use two different pathways when consuming sugars – a respiratory one (with oxygen/aerobic) or a fermentation one (without or with minimal oxygen/anaerobic). Yeast’s choice of pathway has a significant effect on how the fermentation will proceed.

Yeast multiplies through a respiratory pathway (with oxygen) and low sugar concentration (below 0,1 g/L). Those cells are healthier due to their ability to accumulate energy, vitamins, sterols, and micronutrients. They are actively multiplying and producing biomass, and there is a repression of the fermentative metabolism (i.e., no alcohol production).

Conversely, during the fermentation pathway (no or minimal oxygen), and when the substrate has more than 0,1 g/L of sugars (like beer wort), the yeast cells produce alcohol instead of dividing. It’s due to the Crabtree effect. The yeast cells eventually deteriorate due to the increase of alcohol, and the quality of the yeast cells is affected.

Figure 1: Dried yeast production. Starting in the lab with a seed cell and moving to a fed-batch propagation. Followed by separation of the cream yeast and, lastly, filtration and drying.

The challenge during production of beer yeasts (active dry yeast) is to control yeast growth through the aerobic pathway (respiration) for optimal health while avoiding fermentation.

We want the yeast to multiply and remain as healthy as possible (Figure 2). This is done through a fed-batch fermentation, using a computer-controlled process for specific sugar feeding rate and nitrogen.

At Lallemand, yeast growth is monitored to ensure the best quality yeast. Before drying, the yeast cream is evaluated. Protein content, mature cells, trehalose, unsaturated fatty acids, and sterols content (ergosterol) are the main parameters that will determine the drying process’s efficiency and reliability in diverse brewing conditions.

Figure 2: A fed-batch propagation used in the production of dried yeast. The goal is to produce cells instead of ethanol like in a standard fermentation.

Why is active dried brewer’s yeast the best choice for quality beer?

Dried yeast is the most stable form of brewer’s yeast. The purity of the culture limits the risk of contamination found in other types of culture products (e.g., frozen or liquid forms). The way the yeasts are cultivated is designed to ensure good implantation after inoculation and thus dominate the beer wort media, allowing better fermentation control.

Dried yeast is stable in time (2-3 years depending on the brewing strain). Other advantages include:

• Pure and clean of contaminants (including diastatic yeasts)
• Low footprint for storage
• No need for a starter
• High concentration of viable cells
• Can be propagated and/or reused
• No need for oxygen
• Can be pitched dry without the need for extra equipment
• Increasing number of strains available for specific styles

Lallemand Quality Specifications

Each yeast production undergoes approximately 24 rigorous quality tests before leaving the Lallemand plant. Viability, vitality, wild yeast, and bacteria contamination, DNA fingerprinting, and application tests are some of them.

Since dry yeast is stable, a more in-depth characterization can be performed over several weeks to ensure that only production lots meeting our higher quality specifications are released for sale.

Production facilities are separated for all strains exhibiting diastatic ability and brewing bacteria to eliminate the risk of cross-contamination. Furthermore, all Lallemand dried yeast is traceable for each production lot, which is useful for troubleshooting any problems in the brewery, whether related to yeast and fermentation or not.

Shelf-Life and Consistency

Two of the most important attributes of dried yeast, especially when compared to liquid cultures, are shelf life and fermentation consistency.

When properly stored at refrigerated temperatures or lower, fermentations of a dried lager strain are similar over three years after production. You can see in Figure 3 different fermentations over time with the same strain of yeast. This particular strain (LalBrew Diamond™) has a two-year shelf-life since the fermentation takes an extra 24h after 3 years.

Figure 3: The fermentation of the same production lot of Lalbrew Diamond™ lager yeast over 3 years.

Dried yeast is incredibly reliable in fermentation performance. You can see in Figure 4 how different production lots of dried yeast strains display similar fermentations. One reason for this consistent fermentation performance is how dried yeast is produced and packaged.

The ability to know that your fermentation can be so similar over time brings an added level of value to using dried yeast.

Figure 4: The fermentation of 5 different production lots of LalBrew Nottingham™

Rehydration

If you have used dried yeast or are thinking of using dried yeast, you’ve probably heard the term rehydration. Most dried yeast strains can be pitched directly into wort without rehydration (Table 1 illustrates each method’s pros and cons). No loss of activity will accrue if the wort is not too cold, above 15°C, and the conditions not too stressful.

Rehydration is recommended when starting Plato is higher than 16 degrees and for bottle conditioning. Figure 5 shows a graph of four fermentations; two of these were performed with rehydrated dried yeast while the other two were inoculated directly with dried yeast. The results indicate no significant difference between the fermentation profiles inoculated with dried yeast and rehydrated yeast.

Figure 5: Four different fermentations performed side by side with two different yeast strains. In two of the fermentation, the yeast was rehydrated, and in the other two, the yeast was dried pitched.

Table 1: Some of the pros and cons between rehydration and dry pitching of dried brewer’s yeast. While both present good options, it is ultimately up to the preference of the brewer and the brewery setting on how the yeast will be used.

When choosing to rehydrate or bottle condition beers (a process where rehydration is necessary), following a few simple steps can increase success and make the process easier.

– Sanitize the upper part of the pack (e.g., ethanol 70%) and the scissors before opening.
– Sprinkle the yeast on the surface of 10 times its weight in clean, sterilized water at 30-35°C (86- 95°F).
– Leave it undisturbed for 15 minutes, stir gently to suspend yeast completely.
– Leave it for 5 more minutes at 30-35°C (86- 95°F).
– Attemperate in steps at 5-minute intervals of 10°C to the temperature of the wort by mixing aliquots of wort to adjust the temperature of the hydrated yeast, with no delay.

Avoid using revised osmosis or distilled water, as this could lead to a loss of viability. Do not stir right away, as this could break the yeast membrane. Lastly, do not let the yeast come down to wort temperature naturally, as this will take too long and lead to a loss of viability and vitality.

What’s Next? All Eyes on Innovation

Having discussed some of the things that make dried yeast an excellent choice today, you may be wondering what’s next for dried yeast?

Here at Lallemand, we feel that this is a very exciting time with so much innovation on the horizon. The idea of co-fermentation has become more and more popular over the last few years, using two or more strains of yeast during fermentation to produce interesting flavors, stabilize haze, or taming the acidity in sour beer.

This has led us to explore the idea of hybrid strains and how they can be beneficial to the brewer. A hybrid strain is a unique single strain of yeast created through natural cross mutation, combining two relevant traits present in two different strains (i.e., performance and flavor).

Our partnership with Mascoma Labs in the USA has led to the first commercially available dried bio-engineered yeast strain, Mascoma Sourvisiae®. This strain allows brewers to create sour beer during fermentation using the sugars in the wort to produce both lactic acid and ethanol simultaneously.

It is just the first of many new strains created to simplify processes and produce unique flavors. Our innovation doesn’t stop there and includes research and development in non-alcoholic beer and flavored malt beverages, such as hard seltzer. With a future as bright as the one dried yeast has, it is truly an exciting time to be a brewer.

References & further reading:

1. Lallemand Brewing Best Practices – Shelf-life, storage, and pitch rate
2. Lallemand Brewing Rehydration protocol
3. Lallemand Brewing 10 reasons to used dry brewing yeast