Understanding Attenuation

[Fly_Guy]

I am not sure if anyone will have insight into this however last time I brewed I was looking up details on a the yeast I was using and it stated then attenuation was around 65%. I understand what that means.

However is it theoretically possible to get all yeast strains to attenuate to 100% if the conditions were perfect? I understand that this would not be ideal due to how dry the beer would be, but I'm curious what they would need to push attenuation limits of any given yeast strain.

Does anyone know why or what makes some yeast attenuate less than others? Does it have to do with the size of sugars different strains are capable of eating and digesting?

Thank you!

 

[day_trippr]

The only way to achieve 100% attenuation is to eliminate all unfermentables from the wort.
A bit difficult to accomplish if malted grains are involved, even using extraordinarily low mash temperatures for extraordinarily long rests...

Cheers!

 

[Northern_Brewer]

However is it theoretically possible to get all yeast strains to attenuate to 100% if the conditions were perfect?...

Does anyone know why or what makes some yeast attenuate less than others? Does it have to do with the size of sugars different strains are capable of eating and digesting?

Attenuation is a function of yeast strain and wort, so even a poorly attenuating yeast will record an attenuation of 100% if you feed it 100% glucose. So when people say that a yeast has an attenuation of say 65%, they mean in a "standard" wort which is far from 100% glucose.

But yep, it's to do with whether they produce the enzymes needed to unlock glucose from things like maltotriose, which is the big one distinguishing the "69%" yeasts from the "75%" yeasts.

 

[paneubert]

This is why so many people call BS on things like WLP773 and it's claimed 80% attenuation in apple juice. How does it stop when 100% of the sugars are fermentable?

 

[Fly_Guy]

Even if 100% of the sugars are fermentable you would need the perfect amount of oxygen, FAN, and other nutrients to keep them alive and reproducing long enough to eat it all. That's why it was with the caveat of 'in theory'.
Now I'm even more curious to play around with yeasts and compare my attenuation rates with the actual rates. Too bad home brewer is not a career path hahaha

 

[paneubert]

Even if 100% of the sugars are fermentable you would need the perfect amount of oxygen, FAN, and other nutrients to keep them alive and reproducing long enough to eat it all. That's why it was with the caveat of 'in theory'.
Now I'm even more curious to play around with yeasts and compare my attenuation rates with the actual rates. Too bad home brewer is not a career path hahaha

I smell a 773 experiment in my future (when they release it from the vault). I will do my best to use the crappiest store bough apple juice, adjust to the Plato they say gets 80% attenuation, try my best not to introduce any extra oxygen, wont add nutrient, and will keep the temp low. See if it stops at 80%. Haha. I doubt it stops at 80%, but it might be fun to do a side by side with a gallon that I aerate, add nutrient to, etc...

 

[Fly_Guy]

I think many of us would be very curious to see the results of that! Especially if they are significantly different. I'm no statatician, but a few points won't mean as much as a 10% difference between stated aytenuation and actual.

Another interesting experiment would be test how much yeast nutrients do for the actual yeast in a beer with a normal grain bill based only on attenuation.

 

[Northern_Brewer]

This is why so many people call BS on things like WLP773 and it's claimed 80% attenuation in apple juice. How does it stop when 100% of the sugars are fermentable?

"fermentable" is something that depends on the individual organism, it's not a general property of the sugar. So for instance, most yeast can chew up most monosaccharides, but if you had a yeast that ate glucose and fructose, but not galactose, and the apple juice was mostly fructose with some lactose, then you could see that even though it was 100% disaccharides that most yeast would ferment 100%, this particular yeast would only see a 80% fermentable mix.

Alternatively, you just have something that's really sensitive to alcohol and dies when it's only fermented 80% of the typical apple juice.

 

[dmtaylor]

Amylase enzymes such as Beano can be added to any brew to make it up to 90-100% fermentable by most yeasts. This will work, however I do not recommend it. In my opinion, Beano ruins an otherwise tasty beer. It will turn out very dry and watery. I know this from experience. Might be okay for a saison type thing, but not for most other styles.

 

[ESBrewer]

I agree that fermentability of the wort by the yeast in question is the key. But there are more factors than just sugars composition. If the alcohol concentration becomes too high for the strain before 100% is reached it is not going to proceed. Even in the purely hypothetical wort that contains only glucose. In theory, it is the same thing with key nutrients, if yeast runs out of something else before it runs out of glucose, it may stall.

Actually, in such a high glucose wort the apparent attenuation could be even more than 100% as the gravity might go below 1.

But in general, yes, yeasts have the potential to ferment further than the general attenuation estimates suggest. And on real life they often do that.