Predicting attenuation?

Hi all,

Are there formulas for predicting the apparent attenuation of a beer, give the estimated attenuation characteristics of the yeast being used, mash temperature and grain bill? I know that there are other factors that come into play - pitching rates, fermentation temps, etc. - but I'm looking for something just a little more sophisticated than multiplying the OG by the apparent attenuation characteristics stamped on the yeast packet.

This would be useful for setting the mash temp when developing recipes.

The info stamped on the yeast is there for a reason. It's pretty much what you should expect. Taking the OG and the yeast's known attenuation is going to tell you what you need so I'm not sure why you feel the need for any other method. You could achieve results besides what the package says but I believe your best bet is to try and figure out how to hit the exact percentage on the package. Work on your process so that it lines up with what the yeast is designed to do. Knowing what you're going to get before you start is what will help you design the right recipe!

Hope this helps.

cvstrat said:

The info stamped on the yeast is there for a reason. It's pretty much what you should expect. Taking the OG and the yeast's known attenuation is going to tell you what you need so I'm not sure why you feel the need for any other method. You could achieve results besides what the package says but I believe your best bet is to try and figure out how to hit the exact percentage on the package. Work on your process so that it lines up with what the yeast is designed to do. Knowing what you're going to get before you start is what will help you design the right recipe!

Hope this helps.

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No, it doesn't help at all.

Clearly the yeast's attenuative properties are a significant factor (I said that in my original post) but there's much more to it than that. A beer that is mashed at 148 dgf is going to finish much drier than a batch that's mashed at 155. Mash a beer at 170 and you'll get almost no attenuation, no matter what's printed on the yeast packet. Similarly, the FG of a wort made entirely of pale malt will be lower than that of a wort with lots of carafoam in it; a wort with lots of corn sugar will finish lower.

Maybe these equations don't exist yet, but we should be able to do better than just using estimated yeast attenuation and OG to predict FG. I suspect that there's an equation or table floating around that at least factors in mash temp.

TD

ToledoDave said:

No, it doesn't help at all.

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"....thanks, though"? Sounds a bit rude otherwise

If you knew the exact amounts of fully-fermentables and partially-fermentables and the attenuative power of the yeast and the exact temperature you mashed at (minute by minute, unless you held a single temp for the whole time) and exactly how much fermentables you will get at that temperature and how much attenuation you should expect from the yeast at whatever temperature you ferment at and....

Should I go on?

Reno_eNVy_446 said:

"....thanks, though"? Sounds a bit rude otherwise

If you knew the exact amounts of fully-fermentables and partially-fermentables and the attenuative power of the yeast and the exact temperature you mashed at (minute by minute, unless you held a single temp for the whole time) and exactly how much fermentables you will get at that temperature and how much attenuation you should expect from the yeast at whatever temperature you ferment at and....

Should I go on?

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I think that's what the OP is trying to ask, if there is something out there that could take all of these variables into account and spit out an answer. It would be great if one of the programs(Beersmith, promash, Beer tools, etc.) could upgrade to handle this calculation. just a thought.

Reno_eNVy_446 said:

If you knew the exact amounts of fully-fermentables and partially-fermentables and the attenuative power of the yeast and the exact temperature you mashed at (minute by minute, unless you held a single temp for the whole time) and exactly how much fermentables you will get at that temperature and how much attenuation you should expect from the yeast at whatever temperature you ferment at and....

Should I go on?

Click to expand...

You could say the same thing about the formulas we use to estimate OG, bitterness, color, or any other part of the brew process. Just because we don't know every last bit of information about our processes doesn't mean that equations or tables for estimating these processes can't deliver good approximations.

The point is that we do know that mash temps have a significant influence on the FG, and in general what those influences are. We can also do a reasonable job of estimating mash temp, even if it's just the average temp over the duration of the mash. I'm surprised that there aren't formulas available that factor this in.

Does beersmith, promash or any other brewing tool estimate FG? Does varying the mash temp have an effect in these tools?

So I found a couple of excellent resource:

• Homebrew Wiki: The Theory of Mashing

and on Kaiser's site (Thanks Kai!):

• Understanding Attenuation - this is a slightly different version of the Homebrew Wiki of the same name.
• Effects of mash parameters on fermentability and efficiency in single infusion mashing - this is a set of experiments performed by Kai where he varies different mash parameters - time, temp, pH, grind, water/grit ratio, and grain bill diastatic power - does a fast ferment and plots the attenuation of the resulting beers. This is exactly what I'm looking for.

Based on Kai's research we should be able to develop an equation to estimate FG based on OG, yeast attenuative properties and avg. mash temp (assuming a single infusion mash.) Of course this doesn't take into account mash length, grain bill, or anything else, but it should give us a little more accuracy than leaving the temps out.

I'll take a shot at fitting an equation to Kai's data. It's been over 15 years since I did one; hopefully I won't embarrass myself.

I was able to fit a rough curve to Kai's experimental data for attenuation vs. avg. mash temp to come up with a correction factor to attenuation for single infusion mashes:

For avg. mash temps (T) in deg CNote that mf=~1.0 for a mash temp of 66C, less than 1 for other values. This fits reasonably well with the data in the range 60C to 75C

For avg. mash temps (T) in deg FNote that mf=~1.0 for an avg. mash temp of 150.5F, less than 1 for other values. This fits reasonably well with the data in the range 140dgF to 167dgF

This factor can be applied to the standard SG estimate:

SG = (1-mf*AA)*OG

Where AA is the optimal apparent attenuation of the yeast.

Below is the correction factor applied to Kaiser's data. Note that I have taken the optimal apparent attenuation as 90.5%, the average of the two data points at 65.9C
What do you folks think, am I on to something here?

ToledoDave said:

Code:

Batch   temp C   OG    SG    AA%     mf    calc SG
  12     59.9   13.0   2.4   81.5   0.922     2.2
  11     61.9   10.2   1.2   88.2   0.972     1.2
  10     63.3   11.7   1.1   90.6   0.993     1.2
   8     65.9   11.8   1.3   89.0   1.000     1.1 
   9     65.9   11.2   0.9   92.0   1.000     1.1
   7     69.3   14.0   2.1   85.0   0.948     2.0
   2     70.5   13.1   2.6   80.2   0.914     2.3
  15     71.0   16.5   3.8   77.0   0.897     3.1
  13     74.7   15.4   5.0   67.5   0.724     5.3
   6     74.9   13.5   5.0   63.0   0.712     4.8
  14     78.6   16.7   8.9   46.7   0.453     9.9

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I have been trying for the past 20 minutes to figure out what "mf " stands for. Mash something?

toastermm said:

I have been trying for the past 20 minutes to figure out what "mf " stands for. Mash something?

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Sorry - I was thinking 'mash factor', but it's really just an arbitrary symbol.

Coming up with an equation that would work for different people brewing all sorts of different gravities, with different mash techniques, with different pitching rates, different aeration techniques, different pitching/fermentation temps, etc. would probably be very difficult.

But with experience we all are able to predict our apparent attenuation fairly accurately so for a given person/process/etc. (i.e. keeping much of the above constant) and staying within a reasonable range you should be able to come up with an equation.

I just eyeball all the factors and decide that "about 76% for this one sounds about right"...and it's usually close enough. If I were to try a new process; then I'd just be taking an edumacated guess at my %AA. But an equation probably wouldn't be anymore accurate because it wasn't derived from that process.

I guess it just seems that by the time you've come up with an equation you should already have a really good feel for what your %AA will be...and at that point the equation is telling something you already know.

I know this is an old thread, but BackAlleyBrewingCo asked precisely the question that has been on my mind. Using the Brewing Classic Styles recipes, I created a spreadsheet that correlated the mash temps with the expected attenuation for each recipe, and tried to figure out the logic behind it. Some of the recipes are quite confusing -- for instance, all of the Bocks suggest mashing at around 154 - 155, and yet this is supposed to achieve 75% attenuation. In my experience, that mash temp would be way to high for that attenuation level. Anyway, I have been basing my mash temps on the equation I derived from Brewing Classic Styles, and am getting quite variable results. For instance, I just used a single infusion mash at 150 for an APA and obtained 85% attenuation from the fast ferment! No brewing book I have ever read discusses how to approximate your desired attenuation. Clearly this is a fundamental part of all-grain brewing, and any brewer who is not simply following a recipe must have some kind of algorithm that they use to calculate their mash temp based upon their desired attenuation. However, it seems to be a topic that is rarely discussed. Everyone knows that higher mash temps mean less fermentability and lower mash temps mean higher fermentability, but clearly that is not enough information on which to base recipe formulation. What factors do you guys use to estimate your attenuation? What factors that you can control do you take into account?

the best way to predict your attenuation for a given beer it to preform a Fast fermentation test. This way you will know with in a day what the lowest final gravity a given beer will ferment to.

http://braukaiser.com/wiki/index.php/Fast_Ferment_Test

I think there are too many variables calculate any better estimates than what is already available from the yeast data sheet.

Bsquared said:

the best way to predict your attenuation for a given beer it to preform a Fast fermentation test. This way you will know with in a day what the lowest final gravity a given beer will ferment to.

http://braukaiser.com/wiki/index.php/Fast_Ferment_Test

I think there are too many variables calculate any better estimates than what is already available from the yeast data sheet.

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+1 on the FFT.

I do an FFT for every batch I brew and it gives me a much quicker answer to the question of where a beer will finish given the recipe/mash/yeast. I think that gives a better mental association of the process/recipe to the actual result.

The numbers they give you on yeast packs is VERY general. You can very easily get attenuation numbers outside those ranges.

SpanishCastleAle said:

+1 on the FFT.

The numbers they give you on yeast packs is VERY general. You can very easily get attenuation numbers outside those ranges.

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Not only that, but each person's system is different. I have a tendency to overattenuate with every beer I make. Since I know this, I always compensate by using a warmer mash and a less attenuative yeast unless I'm making something that I do want to ferment down to 1.006!

I've been using the same basic setup now for about 1 1/2 years, so I'm accustomed to what I need to do if I want a beer to finish at 1.010-1.012. It's not scientific, but it's predictable.

Yooper said:

Not only that, but each person's system is different. I have a tendency to overattenuate with every beer I make. Since I know this, I always compensate by using a warmer mash and a less attenuative yeast unless I'm making something that I do want to ferment down to 1.006!

I've been using the same basic setup now for about 1 1/2 years, so I'm accustomed to what I need to do if I want a beer to finish at 1.010-1.012. It's not scientific, but it's predictable.

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My beers/system are the same way Yooper, higher attenuation for a given recipe/process than most recipes expect.

I have a theory on this: most start with extract or PM and often struggle to get enough attenuation. So we fudge things (perhaps adding a bit of sugar) to get higher attenuation. As we get more experienced and go AG, our techniques/process improve but we are still fudging things elsewhere (like mashing low) and over-attenuate. So then we have to adjust again because over time we've improved our techniques/process. There can be an element of 'dog chasing his own tail' in this hobby!

SpanishCastleAle said:

My beers/system are the same way Yooper, higher attenuation for a given recipe/process than most recipes expect.

I have a theory on this: most start with extract or PM and often struggle to get enough attenuation. So we fudge things (perhaps adding a bit of sugar) to get higher attenuation. As we get more experienced and go AG, our techniques/process improve but we are still fudging things elsewhere (like mashing low) and over-attenuate. So then we have to adjust again because over time we've improved our techniques/process. There can be an element of 'dog chasing his own tail' in this hobby!

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Interesting thought! I kept trying to fix it- a new thermometer, water chemistry, looking at ingredients, changing mash thickness, etc- but then just said "heck with it" and just always mash a bit higher than I "should".

I know can easily predict my probably FG within a couple of points.

Guys, sorry I was somewhat unclear by referencing attenuation instead of fermentability. What the original poster and I were interested in is how to influence the conditions of your mash such that your wort will acheive a certain level of fermentability. Ultimately what I care about is the attenuation % -- how much residual extract remains in the beer after fermentation -- but my experience is that almost all of my fermentations obtain the limit of attenuation -- i.e. the same attenuation % as my fast ferment test.

So I was wondering what factors you take into account in order to hit your final attenuation? If you are basing your attenuation % on what the yeast packet says, you are probably rarely acheiving your target attenuation, as the yeast have very little to do with the final attenuation. If you habitually underpitch and under-oxygenate, they may have more of an impact, but the mash conditions are what is controlling the fermentability of your wort and the limit of attenuation.

Obviously time and temperature are the two major factors under your control, and your mash pH should be in the appropriate range regardless of what fermentability you want to obtain. So that basically leaves you with the decision about WHAT time and temperatures to use, given the diastatic power of your grist (i.e. whether you are using a 100% pils grain bill, a mostly Munich grain bill, etc.)? What kind of correlations have you found between your mash times / temps / grain bills and the final attenuation that you achieve? Again, there should be rules of thumb for this, but I have not been able to find them. For instance, if you take a Pale or Pils malt, high in diastatic enzymes, and hold it at a given temp for a given amount of time, you theoretically should not see a lot of variation between systems. Different systems differ greatly on their efficiency, but I wouldn't think they would differ a lot in terms of fermentability.

Yooper, since you have repeatability on your system, what is the base mash temp that you adjust up or down, depending on the attenuation % you want to hit? Do you take the diastatic power of your grain bill into account, or do you find that it doesn't make a huge difference?

stoutaholic said:

What kind of correlations have you found between your mash times / temps / grain bills and the final attenuation that you achieve? Again, there should be rules of thumb for this, but I have not been able to find them. For instance, if you take a Pale or Pils malt, high in diastatic enzymes, and hold it at a given temp for a given amount of time, you theoretically should not see a lot of variation between systems. Different systems differ greatly on their efficiency, but I wouldn't think they would differ a lot in terms of fermentability.

Yooper, since you have repeatability on your system, what is the base mash temp that you adjust up or down, depending on the attenuation % you want to hit? Do you take the diastatic power of your grain bill into account, or do you find that it doesn't make a huge difference?

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The DP of the grain doesn't seem to matter in the least. I mean, conversion is conversion. If you get conversion, the DP is adequate. It doesn't seem to affect fermentability in the least.

Also, when I use corn/rice I tend to mash lower and longer. Not because of the corn/rice per se, but because it is almost always a cream ale or another beer style that I want to be more fermentable and finish at a lower FG.

In my experience, using 100% pilsner malt vs 100% other base malt doesn't affect the FG much at all. It's more of the "others" like crystal malt, corn or rice, etc.

If I mash one hour with 1.5 quarts per pound of grain at 153, using just about any base malt, I can plan on getting 1.010-1.012. Using windsor yeast will change that to about 1.017 or so, and pacman will get me to 1.008 or so, but other yeast strains don't seem to matter much.

Adding crystal malts, etc may change that a bit. But not appreciably in small amounts. Simple sugars will, as will a lower mash temp or higher mash temp.

Not Yooper but; I usually hit my FG within a point or two, and it's almost always right at the FG of the FFT. But I mash so differently every time I brew I don't really have a 'base' mash temp. I'll Hockhurz one brew, decoct the next, ramp another, and single-infuse another. If I'm doing a single-infusion, I 'd say 155* F is my 'base' temp. That will get me attenuation near the top end of the 'range' for the yeast, which ime isn't always the same range as the yeast mfr suggests (just look at the alleged identical strains between Wyeast/White, their ranges rarely agree).

Regarding the DP, now that I think about it if I'm using a really low DP/uber-highly modified malt like Maris Otter I generally mash a bit differently than if I'm using a domestic 2-row with really high DP (eg - I'm much more likely to just single-infuse the MO). Or...comparing MO to a less-modified continental Pils; the extra modification of the MO helps it compensate for it's lack of DP but again, I'm much more likely to be decocting/Hockhurzing continental Pils.

That's one of the reasons I change my mashes so much, so I get a really good 'seat-o-the-pants' feel (helped by doing FFTs every batch) for how a mash will affect the fermentability. I don't think I could put it into an equation, it's just a feel thing. Generally I'd rather under-attenuate than over but years ago when I started it was just the opposite.