Everything About Beer Yeast Attenuation – Explained

There is a whole whack of new terms that you need to learn when discovering the joys of homebrewing beer. Worts and mash, lautering and sparging, hops – it can be a lot to take in at the beginning! One of these key terms is yeast attenuation, which can greatly affect the final result. 

Beer yeast attenuation refers to the yeast’s capacity to convert sugars into alcohol. Various strains of yeast have different attenuation levels, and depending on the level, the finished product will have a unique taste and alcohol content!

The remainder of this article will give you everything you need to know about beer yeast attenuation – from what it is and how to measure it to why it’s so important for the final brew!

What Is Beer Yeast Attenuation?

Beer yeast attenuation is a key feature that affects the quality of fermentation. Measured in percentages, it shows how effectively the yeast can consume the sugars in your wort. Some strains of yeast consume more sugars and produce a drier taste; others consume less and offer a sweeter brew.

Knowing the attenuation levels of beer yeast is crucial in the brewing process because it can determine whether you’ll have a sweet or dry brew. 

Aside from the glucose levels in your wort, attenuation can also vary depending on the health of the yeast you’ve pitched. If the yeast is not fresh, its attenuation levels can reduce. 

Varying strains will be low, medium, or high in attenuation levels, commonly posted on the yeast’s packaging. 

Low Attenuating Yeast

Low attenuation levels mean that the yeast will consume less of the glucose molecules during the fermentation process. So, the final brew product will taste sweeter. Low attenuating yeast will fall between 65-70%, meaning the yeast will consume between 65-70% of the wort’s sugars.

Medium Attenuating Yeast

Medium attenuation yeast is ideal because it is in the middle range and thus gives the final brew a balanced flavor. Yeast with medium attenuation will fall between 71-75%. In this context, the yeast consumes up to 3/4 of the sugar enzymes in the wort.

High Attenuating Yeast

High attenuating yeast consumes most, if not all, of the glucose compounds in a wort. As a result, your finished brew will be much more potent and bitter. The percentages for high attenuation range from 76-100%. 

How To Measure Beer Yeast Attenuation

There are a few ways to measure the beer yeast attenuation, which is recorded as a gravity reading. Gravity readings show the sugar content of your brew and determine the quality of your final result. 

You can also use these readings to measure how much sugar the yeast has consumed. By taking these readings before and after the entire brewing process, you can get your yeast’s attenuation level. 

Thus, the first reading is taken from the prepared wort. The second measurement is taken after the fermentation process is complete.

This measurement records how dense (how sugary and boozy) the wort and brew are and can help you decide if you need to add sugar to your brew. You can take a gravity reading in two ways. 

1. Use a Hydrometer

A hydrometer is a digital tool used to measure your brew’s gravity. To use it, you fill the hydrometer with a sample of your wort and let the device do the rest! The density will raise the inner part of the tube to a specific level (marked on the device) to give you a reading.

There are tons of different hydrometers to choose from, and many are calibrated to the gravity levels and temperatures of specific substances. For example, some hydrometers are calibrated to measure the gravity of gasoline, sucrose, or water. 

A hydrometer is a must-have tool for any home-brewing fan. If you are confused by the wide range of products available on the market, check out my complete guide on the best hydrometers for home brewing. 

2. Use a Refractometer

Another method to calculate gravity is by using a refractometer, which uses light refraction to show the sugar contents of liquids. 

A refractometer is quick and incredibly easy to use. It also only requires a few droplets of wort, which reduces the possibility of spilling and/or wasting when trying to extract a sample. 

Regardless of the method, both of these tools will help measure your gravity readings before and after the entire brewing process. To read more about the two devices, check out my article on the differences between a hydrometer and a refractometer. 

How To Take a Gravity Reading

Suppose you’re using a hydrometer to take your wort’s gravity reading. You’ll need a sample of the wort first. Using a mug, mason jar, or small container, scoop out at least ¾ to 1 cup of wort from the main batch.

Pour the sample into the plastic tube 3/4 of the way. Place the hydrometer into the tube and let it rest. The marking on the hydrometer from where it’s fully submerged in the wort is your gravity reading.

If you’re using a refractometer, you only need a few droplets of wort, which provides a faster and more convenient reading. Using a dropper, add your wort sample to the prism of the device. The refractometer will give you the gravity reading on display by looking through the attached eyepiece aimed at a light source.

You’ll need to take readings before and after the fermentation process. The first reading is the Original Gravity (OG) and the second reading is Final Gravity (FG). To get the yeast’s attenuation percentage, subtract FG from OG and divide the result by OG. 

Final Thoughts

In conclusion, beer yeast attenuation refers to how quickly your pitched yeast will eat or ferment the glucose in your wort. The less it does so, the sweeter the final brew will be. However, the amount of sugar and the health of your yeast can affect the attenuation processes. Using a hydrometer will help measure your brew’s gravity before and after the process.