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Old 02-14-2013, 05:53 PM   #1
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Default Yeast Attenuation Versus Mash Temperature

I'm still confused by this issue. Yeast seem pretty hardy and seem to eat all available sugar. My second extract was a sweet stout that finished WAY to high yet every time I have a brew that doesn't finish as low as I think it should the yeast still eat the priming sugar.

I know the higher the mash temps the longer the sugars get. Do different strains of brewers yeast simply stop eating at different points on this chain of sugars. If I took a high attenuating yeast and a low attenuating yeast and split a batch of sugar water would they still finish different?

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Old 02-14-2013, 06:03 PM   #2
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Yeast are mighty little creatures bu they are not fool proof in what they do and require some help.

When you mash at higher temperatures the sugars that are created are more complex sugar chains that yeast find more difficult to consume while at lower temperatures the chains become simpler-this is a very basic explanation to say the least.

It takes a lot of work for the yeast consume the more difficult sugars and in cases they tend to get tired and quit leaving the beer less attenuated than desired. This is especially true if liquid strains are used and no starter was made to ensure proper pitch rate for the given beer.

Priming sugar is a very simple sugar and that is why regardless of what the beer did the yeast have no issues consuming the priming sugar. Simple sugars in the recipe can also pose problems for attenuation if the amounts are large and added in the boil. The yeast will consume these simple sugars first and rapidly and if there is a lot they may not have enough energy to then consume the more difficult sugars leaving the beer stuck or poorly attenuated as well.

SOme strains of yeast are better attenuators than others and this is given as a percentage range and can be found on the manufacture's websites. However, if you don't treat the yeast well they can still have issues with individual grain bills depending on the mash schedule and other factors like pitch rate, temperature, etc.

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Old 02-14-2013, 08:31 PM   #3
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I guess my question becomes, "Is there a standard mash used for testing attenuation across all strains and what are its parameters?"

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Old 02-14-2013, 08:37 PM   #4
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Originally Posted by Hermit View Post
I guess my question becomes, "Is there a standard mash used for testing attenuation across all strains and what are its parameters?"
There probably is/was a very controlled temperature that led the yeast mfrs. to come up with the "average attentuation" for each strain, but keep in mind the word "average". YMMV, which is why one cannot always predict their FG.

In general, mash lower for more attenuation and/or use a higher attenuating yeast, but the complex sugars will almost always produce a less attenuated wort. The grain you use also plays a role as some are not as fermentable (some hardly at all fermentable). Darker grains tend to be this way, roasted grains, etc.

If the yeast poop out due to high OG and increasingly high ABV, sometimes a slight temp raise and agitating of the fermentation vessel can be beneficial, but not always.

The last solution is to add a few drops of amylase enzyme to chop down the long chain sugars and let the yeast chew them further (if you have a stalled beer).
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Old 02-14-2013, 08:48 PM   #5
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Well, you give a good argument for the reason the manufacture gives a range and I understand all of that. The question is why do some yeasts 'eat more' in the same wort split into separate batches. Are they simply eating more complex sugars that the other strain can't or is something else going on?

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Old 02-14-2013, 08:53 PM   #6
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Well, you give a good argument for the reason the manufacture gives a range and I understand all of that. The question is why do some yeasts 'eat more' in the same wort split into separate batches. Are they simply eating more complex sugars that the other strain can't or is something else going on?
Strains are like people, no two are the same. The same height/weight man might be able to lift more weight, or run for longer, strictly due to genetics (without any previous training taken into account). Much like animals have different skills, so do yeast.

Some work fast, others slow, some work a long time, others not so much, some chew a lot of sugars, others don't. Attenuation tells you which will chew the most in general, and which are also alcohol tolerant (so they keep working in a big beer).

You still need to look at recipe and mash temps though because some complex sugars will almost always remain in a beer, so how many you have to begin with is key.

To completely answer your question though, I don't think I've seen yeast mfrs. publish info on "this one eats complex sugars really good!"
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