Selecting the right yeast strain

Selecting the right yeast strain

Published : 01-04-2020 - Categories : Fermentation

The enormous variety of strains on the market can be a bit daunting. At distillique, we sell about 15 yeast strains alone.  We have seen that some people are quite hesitant when we suggest using a different strain than what they are used to. This article will hopefully educate our readers what characteristics to look at when it comes to choosing a yeast strain for a specific style or type of beverage.  

Setting aside preferences for very specific strains from particular companies, there are some general guidelines we can follow when selecting a yeast strain for a particular product. These guidelines are not rules, however, and there is plenty of room for experimentation!

The names or categories used for commercial yeast strains can be a useful starting point, especially for alcoholic beverages in general. Some packaging will specify if it is intended for wine, beer, or spirits. Some will make life even easier and specify the type of spirits (Fruit brandies, Grain-based spirits, Tequila, Molasses and Sugar cane, etc), the type of wine (Cabernet Sauvignon, Merlot, Shiraz, Sauvignon Blanc, Chenin Blanc etc) or even the type beer (Ale, Lager). These are quite self-explanatory. Things can become tricky, however, when making a product with few or no specific yeast, such as mampoer, or when looking for alternatives to the specific yeasts available, such as when using wine yeast for rum production. In these cases, we need to consider several factors. 

Attenuation 

Attenuation is a measure of how much available sugar a yeast strain ferments into ethanol (potential alcohol yield). This may be represented as a percentage or described as high, medium, or low.  

The higher the attenuation, the more sugar has been converted into alcohol and carbon dioxide and vice versa. 

Yeast strains with a low attenuation might leave some residual sugar in your product, meaning not all of the available sugar has been consumed. For beverages such as wine and beer, any residual sugar will influence the taste and mouthfeel, and thus the style of your product. If a dry wine or beer is required, it is best to use a yeast strain with a medium to high attenuation. 

Attenuation is also a big factor to consider for distillers. Although residual sugars won't influence the taste of your spirits, it is still important for economic reasons. Low attenuation means wasted sugar, and this is best avoided if possible to reduce unnecessary costs. As such, distillers would generally prefer highly attenuative yeast strains to minimise sugar waste.

Alcohol Tolerance 

Alcohol is toxic to all microorganisms, and this includes yeast. The alcohol tolerance of a given yeast strain determines how much alcohol it can produce before it reaches toxic levels and kills the yeast cells. 

Yeast has adapted to tolerate higher percentages of alcohol than most other microbes, and some strains tolerate alcohol better than others. This is a result of the selection pressure imposed on the yeast used for different beverages. For example, wine yeasts can tolerate a high percentage (around 15% ABV). Beer yeasts are generally less tolerant, with some examples tolerating 8% ABV but some others up to 18% ABV. Baker’s yeast can be highly resistant to heat but cannot resist high alcohol concentrations (between 6-8 % ABV). Distillers Yeast and turbo yeast can tolerate up to 18% and 21% ABV respectively. The higher the alcohol tolerance (and sugar tolerance) of the yeast, the more sugar you can add to your wash before fermentation in order to have a higher alcohol yield during distillation. 

Yeast producers will specify the alcohol tolerance of a given strain. Although strains can be made to push their tolerance limits slightly, doing so, however, will often produce off-flavours as the yeast become stressed. It is best to choose a yeast that will be able to handle the target alcohol percentage.

Sugar Tolerance

It is important to understand how much sugar (brix) a yeast strain can tolerate. While it may be tempting to aim for a high alcohol percentage in all our fermentations, some yeast cannot handle the osmotic stress created by high levels of sugar. Excess sugar, as well as other dissolved solids in a fermentation medium, will pull water out of the yeast cells, desiccating and killing them.

While Turbo Yeast might happily tolerate 35 Brix, a red wine strain may only ferment at a Brix below 27. It is also important to make sure that the potential of yeast with high alcohol and sugar tolerance (brix tolerance) is not wasted. If a yeast strain can ferment at 35 Brix and produce 20/21% ABV, it would be a waste of the yeasts' potential to only ferment at 20 Brix, unless specific flavour from a strain is the main consideration and lower alcohol content is desired.

Ideal Fermentation Temperature Range 

All yeasts strains function at their best within a certain temperature range. High temperatures, when not controlled, will negatively affect the aromas and flavours of your wine since yeast cells can become stressed. Below the ideal temperature, the fermentation rate will become sluggish or stuck since it will slow down the functioning of the yeasts.

The fermentation temperature also plays a critical role in the sensory components formed during fermentation and should be carefully monitored and controlled. White wines are fermented at lower temperatures (usually below 18 degrees C) whereas red wines are fermented at higher temperatures (usually up to 28 degrees C). Some yeast strains are very sensitive towards the temperature at which they ferment and should thus be carefully controlled. 

For distillation purposes, we would usually ferment at a higher temperature range in order to speed up the fermentation rate in order to start distilling as soon as possible. In some products – like Rum and Sour Mash Whisky – fermentation at a higher temperature than normal is desirable, due to the flavour and aroma compounds formed during these “quick and dirty” fermentations. If such fermentations are your goal, conduct a few small-scale experiments to review the outcomes and see whether your desired yeast strain can handle the higher temperatures. 

Sensory Profile

Perhaps the most important factor to consider when choosing a yeast is the collection of aromas and flavours it will produce. Using the same juice but different yeast trains will produce products with different aroma and flavour profiles.  This is due to differences in metabolic activity between strains. Keep this in mind when you want to produce a product with a specific aroma and flavour profile. Many winemakers and rum distillers play around with different yeasts strains in order to achieve a certain taste and aroma profile. 

Some Examples: 

  • Rhone 4600: apricot and tropical flavours and aromas 
  • Vin 13: passion fruit, grapefruit, gooseberry and guava 
  • NT 116: blackberry and blackcurrant  
  • EC-1118: neutral 

Keep in mind that these are mostly wine yeast and these flavours might differ when used in fermentations made from other raw materials. Other external factors such as temperature, pH, yeast nutrition, aeration etc. also contribute to the yeast performance and thus the products produced. 

pH range 

This is more important for ensuring yeast health than for determining the flavour profile. The ideal pH range is strain-dependent and usually falls in between a pH of 3 and 4 for Fruit and Wine Yeasts, but 4-6 for Beer and Grain Yeasts. The higher its tolerance to low pH, the easier it would be able to survive in very acidic conditions.

A problem occurring in sugar washes is that the pH will drop below that what general yeasts strains can tolerate. To increase the pH and prevent the yeast from dying due to extreme acidic conditions, you can add Potassium Carbonate. But this takes constant monitoring and most likely additions each day. We recommend using our black label turbo yeast for sugar washes since it comes blended with an alkaline buffer, thus allowing the sugar wash to complete without having problems with low pH value. 

There are many other factors that can be taken into consideration when choosing a yeast strain and more can be learned in our Y1: Yeast and Fermentation Foundation course. Choosing a new yeast strain is not that scary when you know what factors to look at. 

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