Terminology question

[lapaglia]

In relation to yeast, what does attenuation mean? How can I use this information to make better wines and ciders?

 

[michael88n]

Attenuation:

Yeast is responsible for turning sweet wort into what we call "beer". Yeast consume the sugar in wort, and turn that sugar into CO2, alcohol, and flavor compounds. When yeast finish the fermentation process, they shut down, clump together, and fall to the bottom of the fermentor, or "flocculate". When yeast flocculate, it is easy to see that fermentation is done. But how can the brewer be sure? What if the flocculation is minimal, and yeast and CO2 stay in solution. How does the brewer really know when fermentation is done? The answer: by testing the degree of attenuation. Apparent attenuation percentage is the percentage of sugars that yeast consume. Attenuation varies between different strains. The fermentation conditions and gravity of a particular beer will cause the attenuation to vary, hence each strain of brewers yeast has a characteristic attenuation range. The range for brewers yeast is typically between 65-85%.

How does a brewer calculate attenuation?

First, the specific gravity must be checked with a hydrometer before the yeast is pitched. Specific gravity is a measurement of density. The specific gravity of water is 1.000, and wort has a higher density relative to water because of the sugars present in wort. As these sugars are consumed by yeast during fermentation, the density and therefore specific gravity measurement lowers. The yeast also produce alcohol, which is lighter than water, so to obtain the "actual" attenuation, alcohol must be removed by heat and replaced by water. Only large breweries go to such lengths to report the "actual" attenuation, while the attenuation most homebrewers measure is "apparent" attenuation. The specific gravity measured before pitching, after correcting for temperature, is called the "OG", or Original Gravity. The OG needs to be logged into a brewers notebook. Then during fermentation, the specific gravity can be re-checked. The specific gravity will fall towards 1.000 during fermentation, and a brewer can learn much about the fermentation by checking the specific gravity of the beer daily. Once the gravity remains the same for 3 days in a row, the yeast is most likely done with fermentation. The specific gravity at the end of fermentation is called "FG", or Final Gravity. To calculate attenuation percentage, the following equation can be used:
[(OG-FG)/(OG-1)] x 100

The only way to know if a yeast has completed fermentation is to check the expected attenuation. Many homebrewers make the mistake of worrying about a beer before they even check the attenuation. A simple check of the specific gravity at the end of fermentation will help in this regard. It is not completely accurate without computing the attenuation. For example, if a high gravity beer is made, the FG will be higher then normal, but the expected attenuation for that yeast strain may have been obtained. To obtain expected attenuation numbers, consult a list of yeast strain attenuation figures.

Most manufactures of brewers yeast list the attenuation ranges of their yeast strains. This can be very useful to a brewer in matching a yeast strain to a beer style. An example would be a brewer wishing to make an American-style Pale Ale. A yeast strain should be selected that will produce a dry finish, and allow for hop flavors to come through. A good choice would be a neutral yeast with an attenuation of 70-80%. If a brewer wants to make an English style mild ale, a yeast strain that does
not attenuate as much would be desired. An attenuation range of 65-70% would be more appropriate. Would a yeast strain that attenuates to 80% taste bad in an English style mild ale? No, but the beer would not taste true to style.



As found here: White Labs

 

[lapaglia]

Thanks for that response. Of course with answers come questions. I used some K1V-1116 with a OG of 1.056 and current SG of 1.002. Using the formula from the article [(OG-FG)/(OG-1)] x 100 I plugged in the actual numbers. ((1.056-1.002)/(1.056-1))*100 = 96.42% attenuation.

1116 has an attenuation of 70%-80%. This is where I am still confused. I currently have 96% and its not done yet. Shouldn't it have stopped at about 80%? Or is it that I didn't have an high enough FG for attenuation to be an issue?

 

[michael88n]

Don't have an answer for that one, but this... I'm not too good at math.

The hydrometer don't lie.

Hopefully a smart person will see this thread and give a good answer.

 

[homebrewer_99]

Thanks for that response. Of course with answers come questions. I used some K1V-1116 with a OG of 1.056 and current SG of 1.002. Using the formula from the article [(OG-FG)/(OG-1)] x 100 I plugged in the actual numbers. ((1.056-1.002)/(1.056-1))*100 = 96.42% attenuation.

1116 has an attenuation of 70%-80%. This is where I am still confused. I currently have 96% and its not done yet. Shouldn't it have stopped at about 80%? Or is it that I didn't have an high enough FG for attenuation to be an issue?

I'll take your word that the math is correct and use your answers...if you kegged the brew at say 75% attenuation and placed it into the cold it would have been fine. If you had bottled at that time and kept the bottles at room temp for a week means it could produce some overcarbonated bottles, but not necessarity gushers.

This is why you should periodically check (sample) bottled brew to make sure it's carbonated at/near a level you like and/or make sure it doesn't become overcarbonated.

By allowing the yeast to attenuate to 1.002 just means it'll have a higher alcohol % and taste "drier" than normal.

 

[lapaglia]

If I have to manually stop the attenuation whats the point of caring what it attenuates at? With my level of understanding it doesn't make any sense yet.

 

[lapaglia]

Is attenuation tied to the alcohol tolerance of a yeast? I notice that those that have a lower alcohol tolerance also have a lower attenuation. As you can see I'm just plain confused. :cross:

 

[perrypainter]

If I have to manually stop the attenuation whats the point of caring what it attenuates at? With my level of understanding it doesn't make any sense yet.

That's exactly the point of knowing the attenuation of the yeast. If you have to manually stop the yeast, to hit a certain gravity without going past it, then you need to get a yeast that doesn't attenuate as much. So that you do not have to "manually stop" a beer.

It's just another "beer nerd" number to pay attention to if you want to completely replicate or control your brew.

At least that's how I look at it.

If you want to know and control EVERYTHING about your beer, then one more thing you need to know the expected attenuation for the yeast you have chosen.

All this is of course IMHO

 

[wildman]

I know this is a 3 year old thread but since its up here I need to clarify that none of this applies to cider. All the sugars are simple and completely fermentable. Attenuation does not apply here.

 

[dinnerstick]

since there's nothing left to say about attenuation, i'll just offer the contentious opinion that cider is indeed delicious. furthermore, tomorrow is september, and the apples are ripening
great thread, see you all in 2014