What do brewers mean by attenuation and how does alcohol tolerance come into play?

[Yuri]

Alright so I'll get straight into it. I'm a microbiologist and I feel like the concept of attenuation means something completely different to me, but probably from similar etymology. I was wondering which of the following scenarios is correct. Let's say we have a hypothetical yeast strain which has an alcohol tolerance of 14%. Let's also say it has a very tight fixed 90% attenuation level. You put in enough sugar to theoretically hit 14% ABV when the gravity goes to 1.000, does attenuation now mean it will not ferment to 1.000 and not hit the 14% cap? I ask because "attenuation" in biology refers to the loss of genes not under selection pressure (for example enzymes that are able to hydrolyse sucrose keeping these sugars in solution). This is confusing because brewers refer to 100% fermented sugars as high attenuation?? If you ferment all sugars that would be more like no attenuation as the yeast is completely competent (has all necessary genes).

I guess my question is, if I use a strain that is said to have attenuation, but I don't add enough sugars for the alcohol cap to be reached, will my batch (in this case mead) always cap out at 90% sugars fermented? Or does attenuation only happen once the strains alcohol tolerance has been reached. I hope to predict the ending gravity with reasonable precision.

*on a side note, if anybody knows the attenuation of Mangrove Jack's BV7 please do let me know as I cannot find it in the specs of the strain.

 

[Stu's Brews]

Attenuation in brewing is used to describe how much of the available sugar has been fermented into alcohol.

If a beer had an original gravity of 1.040 and finished at 1.000, then it would have 100% attenuation as all of the sugars have been consumed.

A more typical result would be a final gravity of 1.010, which would be 75% attenuation.

The level of attenuation you get is dependent on yeast strain, wort composition (the types of sugar in the wort) and yeast health.

 

[Yuri]

Right, I understand that, I just mean, how fixed is this number? Can I reasonably predict a 90% attenuation strain to always go to 90% sugars fermented or are there special cases like really low sugar. Perhaps simpler: Are the attenuation and alcohol tolerance related at all?

 

[Stu's Brews]

Right, I understand that, I just mean, how fixed is this number? Can I reasonably predict a 90% attenuation strain to always go to 90% sugars fermented or are there special cases like really low sugar. Perhaps simpler: Are the attenuation and alcohol tolerance related at all?

Assuming a relatively standard wort composition, then provided you don't exceed the alcohol tolerance for the yeast, you'll get the expected level of attenuation.

Exceeding the alcohol tolerance can reduce attenuation, as the yeast can no longer ferment sugars due to the high levels of alcohol present. However, this is only a problem if making something like an Imperial Stout with a double-digit ABV.

 

[Yuri]

Assuming a relatively standard wort composition, then provided you don't exceed the alcohol tolerance for the yeast, you'll get the expected level of attenuation.

Exceeding the alcohol tolerance can reduce attenuation, as the yeast can no longer ferment sugars due to the high levels of alcohol present. However, this is only a problem if making something like an Imperial Stout with a double-digit ABV.

Thank you! One more question, do you know the exact mechanism for attenuation? Does it have to do with yeast being unable to ferment some sugars? For example, if you add pure glucose would you still see attenuation?

 

[Stu's Brews]

Thank you! One more question, do you know the exact mechanism for attenuation? Does it have to do with yeast being unable to ferment some sugars? For example, if you add pure glucose would you still see attenuation?

Not sure of the full scientific details but different yeast strains are better at consuming some types of sugars than other.

For example, a yeast strain that has the diastaticus gene will have a high level of attenuation as during fermentation it releases an enzyme that breaks long-chain sugars into shorter chains that can then be fermented.

 

[foxy]

Alright so I'll get straight into it. I'm a microbiologist and I feel like the concept of attenuation means something completely different to me, but probably from similar etymology. I was wondering which of the following scenarios is correct. Let's say we have a hypothetical yeast strain which has an alcohol tolerance of 14%. Let's also say it has a very tight fixed 90% attenuation level. You put in enough sugar to theoretically hit 14% ABV when the gravity goes to 1.000, does attenuation now mean it will not ferment to 1.000 and not hit the 14% cap? I ask because "attenuation" in biology refers to the loss of genes not under selection pressure (for example enzymes that are able to hydrolyse sucrose keeping these sugars in solution). This is confusing because brewers refer to 100% fermented sugars as high attenuation?? If you ferment all sugars that would be more like no attenuation as the yeast is completely competent (has all necessary genes).

I guess my question is, if I use a strain that is said to have attenuation, but I don't add enough sugars for the alcohol cap to be reached, will my batch (in this case mead) always cap out at 90% sugars fermented? Or does attenuation only happen once the strains alcohol tolerance has been reached. I hope to predict the ending gravity with reasonable precision.

*on a side note, if anybody knows the attenuation of Mangrove Jack's BV7 please do let me know as I cannot find it in the specs of the strain.

https://brewhq.com.au/blogs/beer-resources/beer-yeast-guide

 

[foxy]

https://brewhq.com.au/blogs/beer-resources/beer-yeast-guide

As BV7 is a wine yeast, wine yeast is 100% attenuation, but not sure how it will go in mead.

 

[Yuri]

As BV7 is a wine yeast, wine yeast is 100% attenuation, but not sure how it will go in mead.

I actually went through the trouble to email Mangrove Jack's and talk to some of my old biotechnology professors. The reason attenuation happens is (as I expected) to do with complex sugars that cannot be hydrolysed by that particular yeast. This attenuation number only counts for the sugar source the yeast are bred for (beer: wort, mead: honey). Because wine is mostly fructose an "attenuation" number usually isn't given as it is irrelevant, wine doesn't contain complex sugars so it will always ferment completely. It doesn't mean wine yeasts don't have attenuation in other types of media. In other words, attenuation is conditional, not fixed. I have set up to test the apparent attenuation of BV7, once I have some results I'll post it back to this thread for anyone looking for it.

 

[Agentgonzo]

If a beer had an original gravity of 1.040 and finished at 1.000, then it would have 100% attenuation as all of the sugars have been consumed.

It's mildly more complicated than that. If it started at 1.040 and fermented all the sugars, the FG would be below 1.000 (because it'd be a mix of water and alcohol and alcohol has an SG of below 1.000). The "real attenuation" would be the percentage of sugars used and in the scenario of 1.040 --> 1.000 it would be less that 100%.

The "apparent attenuation" is what you mention - 1.040 --> 1.000 is 100%.

Apparent attenuation is what brewers mean when they say "attenuation"

 

[Stu's Brews]

It's mildly more complicated than that. If it started at 1.040 and fermented all the sugars, the FG would be below 1.000 (because it'd be a mix of water and alcohol and alcohol has an SG of below 1.000). The "real attenuation" would be the percentage of sugars used and in the scenario of 1.040 --> 1.000 it would be less that 100%.

The "apparent attenuation" is what you mention - 1.040 --> 1.000 is 100%.

Apparent attenuation is what brewers mean when they say "attenuation"

Good catch... I'd had a few beers when I replied

 

[foxy]

I actually went through the trouble to email Mangrove Jack's and talk to some of my old biotechnology professors. The reason attenuation happens is (as I expected) to do with complex sugars that cannot be hydrolysed by that particular yeast. This attenuation number only counts for the sugar source the yeast are bred for (beer: wort, mead: honey). Because wine is mostly fructose an "attenuation" number usually isn't given as it is irrelevant, wine doesn't contain complex sugars so it will always ferment completely. It doesn't mean wine yeasts don't have attenuation in other types of media. In other words, attenuation is conditional, not fixed. I have set up to test the apparent attenuation of BV7, once I have some results I'll post it back to this thread for anyone looking for it.

Something you will have to read up on. Last time I looked using a wine yeast in beer got about 50% attenuation. You want to ferment mead. Google it.

 

[Yuri]

Something you will have to read up on. Last time I looked using a wine yeast in beer got about 50% attenuation. You want to ferment mead. Google it.

Well there is no data on BV7 in mead, or any data on BV7 attenuation at that. The best I could do is run the BV7 genome through Galaxy if it publically available lol

 

[obscure]

Well there is no data on BV7 in mead, or any data on BV7 attenuation at that. The best I could do is run the BV7 genome through Galaxy if it publically available lol

Purely from a practical standpoint mead assuming you are just using Honey is mostly simple sugars glucose and fructose so you will get pretty close to 100% of the sugars being converted to alcohol. If you want a sweet mead you will either need to use a stabiliser to stop the fermentation, or make the mead so high in alcohol that you go beyond the yeasts alcohol tolerance.

Basically much like wine yeasts the assumption is 100% attenuation (also a beer yeast will almost certainly achieve 100% attenuation in a mead unless it gets above the alcohol tolerance of the yeast, as it’s just simple sugars.

 

[YeastFace]

This podcast may be worth a listen -

 

[Yuri]

Purely from a practical standpoint mead assuming you are just using Honey is mostly simple sugars glucose and fructose so you will get pretty close to 100% of the sugars being converted to alcohol. If you want a sweet mead you will either need to use a stabiliser to stop the fermentation, or make the mead so high in alcohol that you go beyond the yeasts alcohol tolerance.

Basically much like wine yeasts the assumption is 100% attenuation (also a beer yeast will almost certainly achieve 100% attenuation in a mead unless it gets above the alcohol tolerance of the yeast, as it’s just simple sugars.

I'm gonna roll with that for the BV7. thanks!

 

[Yuri]

This podcast may be worth a listen -

Will definitely check it out

 

[An Ankoù]

It's all very rough and ready. We don't even measure attenuation accurately we go by "apparent attenuation".
It's not unusual for the FG to be less than 1000 free alcohol is less dense than water. Wines, meads, cider will often end up this way. Beers fermented with "diastaticus" variety yeasts, such as saisons, might, too.
Another factor is the availability of suitable nutrients to the yeast: check out "keeving" in cider production.
So what's the plan, @Yuri? Are you going to make some mead or something else. What are your thoughts on a recipe.
It's a funny business this brewing lark; half way between the kitchen and the lab with some parameters controlled very tightly and others quite roughly if at all. Some of us like to emulate industrial processes down to the nth degree while others rely on sorcery and black magic. What is your motivation. We've had a couple who are fadcinated by yeast properties and they've benefited us all.

 

[matt.]

This podcast may be worth a listen -

That's spooky-- I listened to it last night. Excellent info.

 

[Yuri]

It's all very rough and ready. We don't even measure attenuation accurately we go by "apparent attenuation".
It's not unusual for the FG to be less than 1000 free alcohol is less dense than water. Wines, meads, cider will often end up this way. Beers fermented with "diastaticus" variety yeasts, such as saisons, might, too.
Another factor is the availability of suitable nutrients to the yeast: check out "keeving" in cider production.
So what's the plan, @Yuri? Are you going to make some mead or something else. What are your thoughts on a recipe.
It's a funny business this brewing lark; half way between the kitchen and the lab with some parameters controlled very tightly and others quite roughly if at all. Some of us like to emulate industrial processes down to the nth degree while others rely on sorcery and black magic. What is your motivation. We've had a couple who are fadcinated by yeast properties and they've benefited us all.

Honestly, thinking about it a little bit more there are so many factors (especially the percentage of non-fermentable sugars in honey). And you're right, what's the use testing these things if you are going to neglect other factors? I feel like malt is the same as honey in the non-fermentable regard, although a lot more predictable. What I was going to do was simply ferment with the yeast at different levels of ending ABV under similar conditions and looking at ways to measure the residual sugars, but I am realising now that (as you mentioned), the gravity alone won't do to calculate how much actual sugar is left very accurately. You would basically have to run a GC-MS or something and know exactly the sugars you are targeting for an internal control. Perhaps I will send some samples to a lab to have a GOPOD done or something similar, although an assay for higher sugars of course.

What is my motivation? Honestly I just want to make good meads reliably, using some of my knowledge about biochemistry in the process. If I can help others with that by spreading some of what I have found for myself that would be ideal. I was thinking of running different yeast strains through my software to find out things like what esters or glycerols/polysaccharides they produce under what conditions (if they are inducible etc), but manufacturers are naturally quite secretive about their yeast so I doubt their sequencing data will be publically available. I'm going to experiment a little as I am new to this stuff outside of the lab and have a good think about how I can achieve finding these things out.

Thank you for the suggestion of keeving, I'm going to look into that. Sorry for the rambling!