What are the classifications of yeast?

Although the brewhouse makes wort, it is the yeast that converts wort into beer. Yeast, a fascinating microorganism, has a huge impact on beer brewing. Yeast plays a key role in the unique aroma and flavor of beer and brewing, forming a variety of impressive and unique beer flavors. Without the metabolism of yeast cells, traditional alcoholic beverages cannot be born.
Yeast is a single-celled microorganism belonging to the kingdom of fungi. Unlike plant cells, yeast must not sunlight. Yeast has been a catalyst for making alcoholic beverages for thousands of years. During beer fermentation, yeast converts certain sugars into carbon dioxide, alcohol, and fermentation by-products.
The brewers in the Middle Ages did not know the existence of yeast and its role in beer production. But they often use a “magic” wood pulp to stir a new bucket of wort, and there will be the first few batches of yeast cells on the wood pulp. Next, fermentation will begin within a few hours.
Fortunately, brewers now have deep scientific knowledge of yeast types, metabolism, reproduction, and flavor production characteristics.

Yeast Classification

Long ago, brewers classified two types of brewer’s yeast according to the location of fermentation. The yeast fermented on the top of the fermentor is called the upper fermenting yeast, which is also called Ale yeast. The yeast fermented at the bottom of the fermentor is called the lower fermenting yeast, also known as the large yeast.
Although this classification method can also be used now, it can no longer adapt to the current types of yeast. On the one hand, this classification method cannot cover all Saccharomyces cerevisiae. For example, wild yeast is difficult to be classified as Ale yeast or Large yeast. On the other hand, the simple classification of Ale and Large is of little directional significance for winemakers. Yeast suppliers often use regions and styles for classification and naming. If you want to brew a Belgian-style beer, it is safest to choose yeast with the word Belgium when choosing yeast. But, the negative impact of this “insurance” is to inhibit innovation.

New Yeast Classification

Under such circumstances, George Fix designed a unique classification system for brewing yeast. George Fix divides yeast strains into five major categories and distinguishes them by the flavor characteristics they bring. He divided Al yeast into clean/neutral, wheat-flavored/ester-flavored, and special strains; and divided Lager yeast into dry/refreshing and full/wheat-flavored types.
The classification concept of George Fix focuses on fermentation attributes, not location or style. As a result, slowly more people began to use European Ale yeast to brew an American pastel Al. In this way, the potential of yeast in winemaking can be further developed.

Clean yeast strain

Clean yeast strains are very popular in the United States. As Ale yeast, it has a shorter brewing cycle than Large yeast. But, the wine brewed by this strain has less fruit flavor and low alcohol content, and it can also make people drink some of the clean feelings of Large beer. Also, such yeast strains are relatively easy to control. Its flocculation rate is medium, so it can be kept in suspension for a long enough time and can be adjusted appropriately. But, under high pressure, nutrient deficiency, large temperature fluctuations, or too low fermentation temperature, it is easy to produce trace amounts of sulfur, which will affect the flavor of beer and taste not so clean.

Fruity Yeast Strain

Fruity yeast strains are the type of yeast traditionally used in the UK, but now they are becoming more and more popular in the United States. Compared with Clean yeast strains, Fruity strains can bring more interesting beer, that is, more flavors.
Fruity yeast strains usually ferment quickly and the flocculation time is short. As a result, this type of yeast can make wine faster than Clean yeast strains. These strains tend to form clumps during the flocculation process, and after precipitation, they produce bright, clear beer in a short time.
But, the common disadvantage of rapid fermentation and flocculation is that yeast tends to leave more by-products, such as diacetyl. Depending on the strain, these beers can provide honey, plum, citrus, and sour flavors. Yeast strains in some parts of the UK, Ireland, Australia, and Belgium are usually of this type.

Hybrid yeast strain

The so-called Hybrid yeast strain does not mean that two types of yeast are mixed to ferment, but as Al type yeast, but can be fermented in a low-temperature environment suitable for Lager type yeast.
Traditionally, German old beer and Cologne beer mostly use this type of yeast strain. Because of the characteristics of this type of yeast, Hybrid yeast strains have also been “reused” by more and more winemakers. But, this yeast strain usually has a long fermentation time and a medium flocculation rate, which is not as good as other Ale yeasts. At the same time, it also produces a small amount of sulfur.

Phenolic yeast strain

Phenolic yeast strains are used more in Belgian beer and German wheat beer. Many Phenolic yeast strains usually have high fermentation capacity and low flocculation.
Such strains can produce phenolic and ester characteristics. For example, the pungent sensation and the characteristics of ripe fruits that we taste in German wheat are related to this type of yeast. But the taste of phenols is not a very friendly flavor for people. But skilled brewers can skillfully use these yeasts to produce a pleasant balance of flavors that blend well with other flavors.
These wheat Phenolic beer strains rarely produce detectable levels of diacetyl, but sometimes produce sulfur. Also, most Phenolic beer strains do not flocculate well, so German wheat always looks turbid.

Eccentric yeast strain

None of the beer strains in the above categories fall into this category. Today they are also a type of yeast strain that brewers particularly love. The reason is that they can bring some interesting and strange flavors to beer: for example, soil, barn, leather, a little bit of sourness, etc.
So the representative of this type of strain is what we often call wild yeast. They do not flocculate very well and the degree of fermentation is very high.
These yeast strains are classified according to the previous fermentation position, and all belong to Ale yeast. Below, we will introduce some detailed classification of Large yeast.

Lager yeast

Lager yeast strains are divided into two categories: those that produce drier, cleaner, and refreshing beers and those that are clean but have a richer malt flavor and flavor.
Usually, when choosing to brew most American, Nordic styles and some German rags, brewers will choose yeast strains that are cleaner and have a drier taste. In contrast, yeast strains that can bring more malt flavor are commonly used in Munich Clear Large and Munich Dark Large.

So, how to choose yeast?

When you want to choose a yeast strain for fermentation, knowing your purpose is the first step. Are you going to brew beer that tastes dry or has a heavy body? Is the alcohol content high or low? Are there expectations for the aroma and taste of beer?
Only when you understand what you want to do, can you choose the right strain? Also now, you need to consider the characteristics of yeast:

Apparent Attenuation
Flavor profile
Flocculation
Reliability of supply
Working temperature range

What’s interesting is that winemakers can influence the above five attributes to a certain extent (but very limited) by controlling the recipe, fermentation process, or fermentation conditions. In most cases, changing one fermentation attribute will also result in a change in another fermentation attribute. For example, raising or lowering the fermentation temperature will affect the flavor compounds and the degree of fermentation. All yeast properties are interrelated, and it is almost impossible to change one property without changing the other. So, the application of yeast in winemaking is a test of the level of a winemaker.

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