Yeast is the unsung hero in the world of spirits production, especially in whisky.
While enthusiasts may discuss the quality of raw materials, the craftsmanship involved in distillation, or the casks used to mature the whisky – it’s the tiny, single-celled microorganisms known as yeast that create the alcohol and the complex flavour profiles we enjoy.
You can’t make good whisky without a good wash!
This article aims to shed light on the crucial role of yeast plays. It touches on how it influences fermentation and the factors you should consider when selecting yeast strains.
If you are new to the distilling process, the following will increase you base knowledge. If you are planning a new whisky distillery, it’s help form some opinions on what you need to get right for your budding operation (yeast pun intended!).
The biology of yeast
Yeast belongs to the Saccharomyces genus, with S. cerevisiae being the most commonly used in distilled spirits production.
To state the idiotically obvious here… but yeast cells are extremely small and require a microscope to be seen. To understand it, you’ve got to look at the cellular components that enable it to grow and ferment.
The yeast cell consists of an outer cell wall and an inner plasma membrane. These serve as structural support and a regulatory barrier for material exchange. The internal components of yeast cells—like the nucleus, vacuole, and mitochondria—are essential for their growth and fermentation processes.
For those interested in finding out more on this, we will have a separate expert article on the subject soon.
Yeast’s role in fermentation
The fundamental role of yeast is to convert fermentable carbohydrates into alcohol and other flavour compounds. Yeast can function in both aerobic and anaerobic conditions, but it’s under anaerobic conditions that alcohol is produced.
In this exothermic reaction, yeast transforms carbohydrates into alcohol, carbon dioxide, and other flavour compounds while releasing energy in the form of heat. For more on this, see our article on Fermentation. We also have a specific one for Whisky Fermentation.
The key takeaway – strains matter!
Distillers often employ various strains of Saccharomyces cerevisiae to influence the taste, aroma, and overall profile of their spirits. Each yeast strain comes with its own unique set of characteristics, such as alcohol tolerance, fermentation speed, and flavour contributions.
For example, there’s the off the peg DADY Yeast (Distillers Active Dry Yeast). This is a general-purpose variety, used for multiple types of spirits with high alcohol tolerance and ferments sugars quickly. Alternatively, there’s California Ale Yeast produces clean flavours with a balanced profile. Meanwhile British Ale Yeast produces a slightly fruity and more complex flavour profile by comparison.
There are so many more making a list would be endless. For example, there’s the esoterically named Pepenero or Toro Nero and Pinnacle M/MG+ and those fresh out the lab (who have little sense for the grandiose and stick to digits in their naming conventions) DY379, DY502, US-05, S-04 and N379.
There are specialist yeast suppliers that can provide a variant that will bring out the full-bodied nature of a malt, or work well at a wide temperature range. Some can even isolate and cultivate pure culture yeasts. These offer the chance for more consistent fermentation performances, predictable alcohol concentrations and the ability to produce specific flavour compounds.
The strain you choose will depend on your desired fermentation speed, flavour profile, and the specific requirements of your raw material. If you are planning your process, it’s time to nerd out and trial a few variants.
Yeast types: Cream, pressed, and dried
Irrespective of the specific strain of Saccharomyces cerevisiae, Yeast can be sourced in various forms (types) — cream, pressed, and dried — each with its own storage requirements.
Most distillers opt for either dried yeast or pressed yeast. Dried yeast has a longer shelf-life and is often preferable for smaller operations with limited storage facilities. Meanwhile, pressed yeast requires cold storage, and is better suited for medium-scale productions.
All those who ferment their base spirit need to put in practices to ensure that theirs remains potent and viable.
Start with maintaining the right temperature in a Temperature-Controlled Environment. The temperature should be constant to avoid fluctuations that can reduce yeast viability. Humidity levels need to be controlled to prevent the yeast from deteriorating too. High humidity can lead to moisture seeping into the yeast storage containers, which can activate the yeast prematurely or cause mould growth.
Ensure that older stocks are used before newer ones, it’s essential to have a well-organised stock rotation system. This sounds obvious, but it is easy to overlook when you are having to monitor a dozen things and this is just one of the morning’s dozen urgent jobs.
Local and global considerations
It’s important to consider local climatic conditions when selecting and storing yeast. It’s clear to see how ambient temperature will play a role during fermentation. Too cold, and yeast activity slows down, prolonging the fermentation process, too hot, and the yeast can die or produce undesirable flavours due to the overproduction of certain compounds. These can be easily mitigated however.
There are also regulatory and commercial aspects (supply chain) to consider within each region. For example, there may be regulations may limit the types of yeast and additives you can use.
More difficult (read expensive and time consuming) to alter is a region’s water quality.
Water influences yeast selection
Water is a fundamental ingredient in whisky production, making up the majority of the mash that will be fermented by yeast. The quality of water used can have a profound impact on the activity of cultured yeast. Ultimately this affects the efficiency of the fermentation process and the final flavour profile of the whisky.
High concentrations of minerals like calcium, magnesium, and sulphate can affect yeast metabolism. While some minerals like calcium and magnesium can positively influence yeast health and flocculation, excessive amounts might lead to off-flavours or even hamper yeast activity.
Meanwhile, Chlorine and Chloramine are commonly found in tap water and can be detrimental to yeast health so they need to be removed through filtration.
Don’t forget that water pH can influence the pH of the mash and subsequently, the yeast environment. The hardness of water, which is a measure of dissolved calcium and magnesium ions, can influence yeast performance.
High levels of dissolved oxygen can adversely affect yeast during the anaerobic fermentation phase too.
Where you distil, the water and the climate affects your choice of yeast as much as the type of product you want to make. Look at it holistically to ensure our selection is both compatible and compliant!
The building block to great spirits
Yeast is more than just a catalyst in the production of spirits. It’s a critical ingredient that influences everything from alcohol content to flavour profile.
By understanding the biology of yeast and the factors that influence its effectiveness, distillers can make more informed decisions that elevate the quality of their spirits. Considering local conditions and regulations, and keeping an eye on advancements in yeast technology can make a significant difference in the quality and uniqueness of your product. Therefore, the importance of selecting the right yeast strain for your distillery cannot be overstated.
For those interested in continuing their research into making whisky, have a look at our Whisky Fermentation article. For those whose interest is more rum or brandy lead, there are articles on Rum Fermentation and Brandy Fermentation too.
