Yeast - How to use

How to estimate the amount of yeast for your fermentation

The amount of yeast needed will depend on several factors such as:

• type of yeast

• style of beer

• gravity (OG) of the Wort

• how many liters of beer will be produced.

The main information to be analyzed is the amount of cells that will be needed to ferment the beer in question.

Depending on how many cells are present in the yeast you intend to use, you may be able to assess the need to increase this amount (either using a starter or using more than one packet).

A study by Brewers Friends indicates that a packet of dry yeast has between 8 to 20 billion cells per gram. By then we can already see that it is not a simple matter and that there are very considerable differences.

But then what is the solution?

We can use as a reference the recommended dosage that appears on the yeast package.

According to information from yeast manufacturers, there is a consensus that 1 sachet (around 11g) is enough to make 20 liter brews.

However, we need to take into account some variables before following this reference:

• Is the yeast past the expiration date?

• Has it been conditioned at proper temperatures?

If everything is OK, the next question is:

• What is the original density of your wort?

It is normally indicated that for lighter beers, with OG up to 1030, the dosage recommended by the manufacturer can be followed. The higher density beers will need more yeast.

In this case, for most Ales it is recommended 1 pack for up to 20L, two packs for 25L to 40L, etc.

To be 100% correct, it would be necessary to count the cells under a microscope.

Enough cells in the fermentation prevent off-flavours in the beer. This is because, with the low amount of yeast, they will need to work twice as hard to handle all the sugar, generating by-products that can cause unwanted aromas and flavors.

Therefore, when in doubt, it is always better to use too more yeast than too less.

Main yeasts used in brewing production

Yeasts used in the production of beer belong, in most cases, to the genus Saccharomyces. For the manufacture of Ales, Saccharomyces cerevisae is used , while the species most used in the fermentation of Lagers is Saccharomyces uvarum.

Each of them has different strains, which you must choose according to the characteristics of the beer you intend to produce.

There are yeasts on the market for different styles. When in doubt, seek the manufacturer's instructions. But if you want to know a little more about the subject, it's good to know what are the main elements that make the difference from one yeast strain to another.

Elements that differentiate yeast strains

Before buying a yeast , you need to define some characteristics of the beer you want to make: whether you want a higher or lower alcohol content , with a “cleaner” taste or not, with a “drier” finish or not, and so on.

According to your intentions, you should choose a different yeast. For this, it is necessary to know the main characteristics that differentiate the different yeast strains.

See below what they are and how yeast S-04 and US-05 behave in these terms, the two most used by home brewers for production of Ales.

Alcohol tolerance

There are yeast strains with greater and lesser tolerance to alcohol. Depending on the style of beer you want to make, this data can be crucial.

If you want to produce a beer with 5% or 6% alcohol content, you don't have to worry too much about it, because any strain will work well. Now, if you plan to make a Barley Wine, for example, which has an average of 10% alcohol, you need to choose more resistant strains. Otherwise, the yeasts will die and they won't be able to attenuate your wort.

The different strains have a varied tolerance level to alcohol. To produce beers with high alcohol content, you should use more resistant strains. Otherwise the yeasts will die and will not attenuate the wort. The alcohol tolerance of the US-05 is high, while that of the S-04 is medium.

Atenuation

Yeast can have high, medium, or low attenuation capabilities. The greater this capacity, the greater the potential for consumption of fermentable sugars (maltose, sucrose and fructose, for example).

A yeast with high attenuation will “dry out” a lot , leading to a lower final gravity (FG ) (below 1.0010). Conversely, if the yeast has a low attenuation capacity, the FG will get higher (more than 1.015).

Strains can have high, medium, or low attenuation capabilities. The greater this capacity, the greater the potential for consumption of fermentable sugars . A yeast with high attenuation will “dry out” a lot, leading to a lower final density, whereas a strain with low attenuation will lead to a higher final density. S-04 and US-05 yeasts have medium attenuation.

Flocculation

Flocculation is the ability of yeasts to agglutinate, separating from the wort after some time in contact with it. Like attenuation, it can be high, medium, or low.

The greater the flocculation of a yeast, the faster it will clump together. This means that it will spend less time in suspension in the wort and, consequently, will provide less attenuation.

Yeasts with less flocculating capacity, on the other hand, will remain suspended in the must for longer. This is the case of those used to make wheat beers, known for their greater turbidity.

Like attenuation, flocculation can be high, medium or low. The larger it is, the faster the yeasts will clump together. In other words, the yeast will spend less time in suspension in the must, promoting less attenuation. On the contrary, yeasts with less flocculating capacity (such as those used to make wheat beers) will remain suspended in the wort longer, which is interesting for making beers that need to consume diacetyl at the end to avoid off flavors . The flocculation of the S-04 is high and that of the US-05 is medium.

Fruity character or esterification

Different strains of yeast produce varying amounts of esters during fermentation. The more esterified strains produce more esters which can be off flavors as highly desirable flavors, depending on their concentration and the style of beer in question.

A Belgian Ale , for example, calls for a well-esterified yeast. But if you want a clean beer , with a “pulling” flavor for hops or malt, the request is to use a neutral yeast strain.

A good experience would be to ferment half batch with S-04 and the rest with US-05 and see the result.

This will help you better understand how the fermentation process works and have more sensory input to choose the right yeast strain. And then you can still make a blend and see what happens.

Different yeast strains produce different amounts of esters during fermentation. If you want to make a Belgian ale, for example, you must use a well-esterified yeast. But if you want a clean beer, with a “pulling” flavor for hops or malt, the best option is to use a neutral strain. Esterification is what most differentiates the two yeasts analyzed in this post. While the S-04 has a high fruity character, the US-05 is neutral. As a rule, English-style beers go well with the S-04, and American-style beers with the US-05.