Author Topic: Estimated Attenuation Calculation Step Mash  (Read 1220 times)

Offline Dirtywaltzer

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Estimated Attenuation Calculation Step Mash
« on: May 28, 2020, 11:39:58 PM »
I have an issue with Beersmith3 and the parameters it uses to calculate the estimated attenuation. My mash profile is a step mash with rests at 61degC (142degF) and 69degC (156degF). It appears that BeerSmith3 is using the lower temperature step in its formula and calculating an abnormally high estimated attenuation of 88.4%. The yeast strain I have loaded into the recipe has a fermentation range of 72-82% attenuation. I suspect there may have been an update to the formula BeerSmith uses to calculate estimated attenuation as in past recipes it appeared to only use the higher mash rest temp when calculating the estimated attenuation.

My question is what parameters/ formula is it using to estimate attenuation?

Is there a setting somewhere where I can limit or adjust the parameters used for this calculation?

Offline Oginme

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Re: Estimated Attenuation Calculation Step Mash
« Reply #1 on: May 29, 2020, 06:24:21 AM »
There is a general misunderstanding of the numbers that the yeast companies publish for apparent attenuation range.  This range given is a test specification of the expected attenuation of that strain when used on a standard laboratory wort.  Your actual wort may vary greatly in content from what this standardized laboratory wort contains for sugars, dextrins, and non-fermentables.  Given this, it is very possible to have a wort which will attenuate much higher (or lower) than the attenuation range for a given strain.

Simple sugars will attenuate completely greatly increasing the attenuation.  Your mash temperature will determine the ratio of fermentable sugars versus longer dextrins which are unfermentable by the yeast.  Your fermentation temperature will have some affect on how much of the sugars get consumed before the yeasts run our of gas and cannot process more.

Add to this that the model used in almost every brewing software (all of the ones that I have trialed for sure), estimate the fermentability of a wort based upon a single rest temperature.  The main reason for this is because there are no good details on how much of an impact multiple rests in the saccharification range will have.  There are just too many variables to take into account (time at temperatures, mash thickness especially if the raise in temperature is due to further infusions, decoctions, pitch rate, etc.) for anyone to model accurately.

The change from BS2 to BS3 is that Brad removed a limitation on the fermentability range.  Previously, he had set a limit where temperatures below 146F (63.3C) were not considered as affecting the fermentability of a wort.  In your previous cases, this means that your 61C (142F) rest would not have been taken into consideration and the program would have used the only rest in the saccharification range [69C/156F] to estimate the fermentability of the wort.

Personally, I don't place a lot of stock in the FG estimations when I do step mashes, as there are too many other variables which the program simply cannot predict.  If I want to know the bottom limit a wort will achieve, I run a fast ferment test and use that as a guide.
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Offline Dirtywaltzer

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Re: Estimated Attenuation Calculation Step Mash
« Reply #2 on: May 29, 2020, 11:50:54 AM »
Quote
Posted by: Oginme
? on: Today at 06:24:21 AM ?Insert Quote
There is a general misunderstanding of the numbers that the yeast companies publish for apparent attenuation range.  This range given is a test specification of the expected attenuation of that strain when used on a standard laboratory wort.  Your actual wort may vary greatly in content from what this standardized laboratory wort contains for sugars, dextrins, and non-fermentables.  Given this, it is very possible to have a wort which will attenuate much higher (or lower) than the attenuation range for a given strain.

Simple sugars will attenuate completely greatly increasing the attenuation.  Your mash temperature will determine the ratio of fermentable sugars versus longer dextrins which are unfermentable by the yeast.  Your fermentation temperature will have some affect on how much of the sugars get consumed before the yeasts run our of gas and cannot process more.

Add to this that the model used in almost every brewing software (all of the ones that I have trialed for sure), estimate the fermentability of a wort based upon a single rest temperature.  The main reason for this is because there are no good details on how much of an impact multiple rests in the saccharification range will have.  There are just too many variables to take into account (time at temperatures, mash thickness especially if the raise in temperature is due to further infusions, decoctions, pitch rate, etc.) for anyone to model accurately.

The change from BS2 to BS3 is that Brad removed a limitation on the fermentability range.  Previously, he had set a limit where temperatures below 146F (63.3C) were not considered as affecting the fermentability of a wort.  In your previous cases, this means that your 61C (142F) rest would not have been taken into consideration and the program would have used the only rest in the saccharification range [69C/156F] to estimate the fermentability of the wort.

Personally, I don't place a lot of stock in the FG estimations when I do step mashes, as there are too many other variables which the program simply cannot predict.  If I want to know the bottom limit a wort will achieve, I run a fast ferment test and use that as a guide.

Thanks for the summary Oginme. That change in the fermentability range explains the output I am getting. I have a pretty good idea of what to expect from this yeast from previous brews. Hopefully someone can come up with a model to account for step mashes in the future. Cheers.