Attenuation question

[blasterooni]

So I have been reading up on attentuation (apparent attenuation to be clear), and I am finding that the percentage of attenuation is a little confusing to me. For example, say a yeast is rated at 75% attenuation, and if the OG is 1.050 you should expect fermentation to be complete at 1.010. Well, I have a yeast that is 75% but I am already below 1.010. Am I missing something? Further, if this is the case, how can one ferment to complete dryness unless the yeast is 100% apparent attenuation? Or is the hydrometer calibrated to give a reading of complete dryness (when apparently reached) yet there are still fermentable sugars in the wort/must? Or am I way off base and missing the point?

 

[Smellyglove]

So I have been reading up on attentuation (apparent attenuation to be clear), and I am finding that the percentage of attenuation is a little confusing to me. For example, say a yeast is rated at 75% attenuation, and if the OG is 1.050 you should expect fermentation to be complete at 1.010. Well, I have a yeast that is 75% but I am already below 1.010. Am I missing something? Further, if this is the case, how can one ferment to complete dryness unless the yeast is 100% apparent attenuation? Or is the hydrometer calibrated to give a reading of complete dryness (when apparently reached) yet there are still fermentable sugars in the wort/must? Or am I way off base and missing the point?

The yeast spec % is just a number achieved in the lab facilities with a standard wort. Some times they are correct, other times they are not so much correct. It's just a ballpark, which can be pretty off. Look at WLP565 for instance. If one get those numbers something is wrong, as it ferments most often way drier than that.

 

[dmtaylor]

Yeast is a living organism. They'll do what they want, and not always the same thing twice, even if that's what we would prefer. There are also a lot of variables with different kinds of complex vs. simple sugars in different beer worts, depending on grist, mash parameters, etc., which the yeast have an easier or harder time dealing with from batch to batch. Expect final gravity and thus attenuation to vary between batches and from manufacturer specifications. They can only provide an average or a range, not an exact value.

FYI, Wyeast 3711 and Belle Saison yeasts, as well as other so-called diastaticus yeasts, can ferment up to 96% apparent attenuation for a consistent FG of about 1.002, given the right conditions and enough time for them to finish. Patience is also a factor.

Another FYI, if fermenting cider, wine, or mead, it is very common for a final gravity below 1.000 down to about 0.992-0.994. This is because alcohol is less dense than water, and unlike a malt wort, the simple sugars are easier to ferment to high alcohol levels in these beverages. But again, patience is a factor...

If any fermentation is rushed, the "final" gravity can appear higher than expected if a slow fermentation is still going on. When in doubt, ferment longer to ensure FG has been reached. And then also don't be surprised if it's lower than you expected. The yeasts are alive and they'll do what they want. You can try to control final gravity and attenuation via ingredients and mash parameters, and the biggest choice being selection of the yeast strain..... but they'll still do what they want.

 

[Qhrumphf]

You can calculate a ballpark based on how you brew it (gravity, wort composition, mash parameters, etc) but different worts will be fermented different ways by the same yeast. Listed attenuations (or ranges) are "average". You can easily (and predictably) push attenuation well below or above those numbers.

One of my favs is listed as 67-72% apparent attenuation if I recall. I've (deliberately) manipulated it as low as 50% or as high as 85%.

Consistent process and ingredients is really the only way to know where something is gonna finish before you do it- and that's only because you've done it before. Same beer brewed the exact same way with the same yeast should finish about the same (and even then a margin of error based on miniscule differences). If you see wild swings in that case there's something wrong.

 

[balrog]

say a yeast is rated at 75% attenuation, and if the OG is 1.050 you should expect fermentation to be complete at 1.010

I think 75% attenuation would ferment 1.050 down to 1.020.

50-10 = 40
40/50 = 80%

75% would be
50 * 75% = 30
50-30 = 20
FG expected = 1.020

 

[archthered]

One thing I have heard that affects this is that not all sugar is the same, if you mash high or add alot of crystal malt to increase dextrins you have a higher % of sugar that the yeast simply can not eat not matter what so you end up with a lower (or if you do certain things even higher) attenuation than the number given depending on nature of the sugar in your wort. In fact, if I have been told correctly, since a standard wort is used with know quantities of different sugars etc the yeast with a higher attenuation primarily get that higher number by being able to eat more of the bigger sugars than other yeast so you can't expect the % given to be completely accurate. Basically you have to take your worts composition compared to the lab standard in to consideration when estimating what you will get.

Also

I think 75% attenuation would ferment 1.050 down to 1.020.

50-10 = 40
40/50 = 80%

75% would be
50 * 75% = 30
50-30 = 20
FG expected = 1.020

Your math is off 50*.75= 37.5 meaning the FG would be 1.0125, I would assume blasterooni, who was also wrong, was just ballparking the math in his head, ending up pretty close

 

[Jag75]

Sometimes the grain bill or boil additions effect it. For instance I did a pumpkin ale that was supposed to be around 1.053. It came in at 1.058/59. I used wlp001 and was expecting a FG of approx 1.012 . Well it actually got down to 1.003. Maybe it was the 60 oz of pumpkin I used in the mash , maybe it was the lb of brown sugar I used late in the boil.

 

[balrog]

Your math is off 50*.75= 37.5

dang i hate when i calc/type/talk to fast
Thanks

 

[blasterooni]

Ok, I think I have the answer to my question... I think. My confusion was how can a yeast ferment to dryness when it was only expected to ferment X%. It appears that the expectation is based on beer wort, which seems to have more complex sugars than cider (which is what I make), some of which are not fermentable. And, as another member posted above, yeast will eat up the [fermentable] sugar so long as it is available, seems to make sense since, at least with cider, one can get to total dryness or very close. As a noob, I also confused the notion of 'attenuation' and 'alcohol tolerance' and the relation between the two. I assumed that the yeast would consume fermentable sugar to a point that the alcohol volume would essentially "kill off" the yeast thus stopping further fermentation. At the end of the day, it seems that attenuation is not all that important for making cider since we are dealing with mostly simple sugars that the yeast can take care of as long as it is alive and healthy and the alcohol content is still within range such that the yeast isn't killed off. Again, this idea may be due to my noob status.

 

[blasterooni]

To make sure I understand the math here is an example to see if I got it right:
EX.: Attenuation = 67%
SG = 1.060

.67(60)= 40.2
60-40.2=19.8
Expected FG = 1.019

 

[dmtaylor]

FYI to you and to moderators: You initiated this question about cider on the 'Beginners Beer Brewing Forum'. Would be more appropriate on a Cider forum -- cider is not beer!!

Since you are making cider, you should indeed ignore the attenuation rating, and expect every cider to quit fermenting between 0.992-1.000, for a standard strength cider in the 6-7.5% ABV range. If adding a lot of extra sugars to bring alcohol level up above that range, the alcohol tolerance can come into play. Most yeasts can tolerate 8-9% ABV with ease. When ABV gets much higher than that, the tolerance kicks in. When this occurs, the yeast don't die, they just become tired and "drunk" and settle out and won't ferment any farther. Some folks will select a low-tolerance yeast and add sugar to bring final gravity up to 1.010 or whatever. Personally I don't but to each his own. But yeah, I think you understand now... and WE understand that you are making cider, NOT BEER!

 

[blasterooni]

FYI to you and to moderators: You initiated this question about cider on the 'Beginners Beer Brewing Forum'. Would be more appropriate on a Cider forum -- cider is not beer!!

Oops! Sorry about that, meaning putting this in the "beer" section. I figured it was a "beginner" question, and I didn't realize that there was a difference, with respect to the initial question, between attenuation as pertains to beer and as to cider. But, that is all cleared up now

I suppose I could write up a little blurb in the Cider section in the event that another noob cider maker gets tripped up on the attenuation issue