Zymurgy's Geeks Article: Hitting your Target Gravity

[Kaiser]

I just got around to browse through the latest Zymurgy and found the target gravity article by Steve Holle. And this article could almost be based on my efficiency work. Only that he assumes that brewers can easily get to 100% conversion efficiency and that the grain absorption rate is 0.115 gal/lb. Both assumptions are not correct. I had to introduce the idea of the conversion efficiency which can be significantly less than 100% if the mashing conditions are poor. And the 0.115 is the apparent wort grain absorption if the volume increase that is caused by the dissolved sugars is neglected. The real wort absorption is closer to 0.19. This actually matters as it changes the efficiency numbers.

Just in case anybody cares.

Kai

 

[JMSetzler]

Rdwhahb

 

[z987k]

Rdwhahb

no, this is rather important to us that really care.

 

[Edcculus]

Good point Kai. Like you have said in previous threads, we shouldn't assume 100% extract efficiency.

Specifically, what mashing conditions would cause lowered extract efficiency? Unstable temp, uncalibrated temp, wrong water/grist ratio?

Also, about grain absorption. I don't know what I have set up in beersmith. I know its at default. Should I go back and change it to something closer to 0.19?

 

[Boerderij_Kabouter]

Just use Kai's efficiency spreadsheet from his site. It is cool to have as a record from brewday.

 

[Laughing_Gnome_Invisible]

Rdwhahb

When Kaiser speaks it is time to listen.

This is not a topic that concerns me too much right now, but one day I hope I will know enough about brewing that the finer points like this will be gold.

 

[Edcculus]

Just use Kai's efficiency spreadsheet from his site. It is cool to have as a record from brewday.

I'll have to check that out. I'm always on a Mac with no excel at work and keep forgetting to download it when I'm at home.

 

[AnOldUR]

Also, about grain absorption. I don't know what I have set up in beersmith. I know its at default. Should I go back and change it to something closer to 0.19?

I've always calculated it manually and added it to BeerSmith's "Boil Volume" to figure how much water I need. I've adjusted the other settings so that this method comes pretty close every time. Is there a default value for grain absorption in BeerSmith that I missed? I don't see it in the Equipment Details.

(I've been using .18 gal/lb)

 

[Edcculus]

I don't have it up. I thought I remembered seeing something to account for grain absorption though. I'll look when I get home.

 

[Kaiser]

Thanks for the support. I posted this in the science forum for a reason. There is no RDWHAHB here , it is about the science and not so much about making beer. I have a little more relaxed attitude when it comes to making beer. Hard to believe but true.

Do NOT change the water absorption in Beersmith to 0.19 gal/lb. The absorption rate in there wants to be around 0.12 gal/lb, which is what I call the apparent absorption as it does not account for the volume of the dissolved extract (more general word for sugars, dextrins, proteins and other stuff dissolved in the wort). And you want it that way. It is much simpler. You only need the real absorption (0.19 gal/lb) when you are trying to predict no- and batch sparging efficiencies.

I e-mailed Steve and he was very quick in his reply. There was no intention on his side to assume that brewers would get less than optimal conversion in the mash but we are still in disagreement over the grain absorption rate that should be used. The reason why I’m so picky and stubborn about this is b/c I started out with that assumption (0.12 gal/lb) when I analyzed a batch sparging model but was not able to make the numbers match my measurements until I accounted for the volume that is contributed by the dissolved extract.

Kai

 

[Kaiser]

Btw, this is the same author who wrote the controversial batch vs. fly sparging article in BYO.

Kai

 

[Edcculus]

I missed that one. Do you have a link?

 

[Kaiser]

This is the discussion we had here: https://www.homebrewtalk.com/f36/batch-vs-fly-steve-holle-article-byo-55164/

there were more lengthy discussions on other boards.

Kai

 

[bob1852]

Thanks for posting this Kai - when I read the article today, I thought: hmmm, I wonder what Kai thinks about this, as some of it didn't make much sense to me compared to what you've posted here, on your blog, and on wiki.

thanks.

 

[Kaiser]

Last night I finally took the time to recalculate Steve’s table and I also noticed another rather confusing point. The efficiency that he is giving is based on the total weight of the grain and not the extract potential of the grain. If you base your efficiency on the total weight of the grain the best you can get will be the grain’s extract potential (generally between 76 and 80 for base malts when you take moisture content into account). If you based the efficiency on the extract potential the limit is 100%. It is common practice in German brewing (home and commercial) to base efficiency on the grain weight but this is unheard off in American home brewing. As a result his efficiency numbers are by a factor of 0.75 lower than they should be.

Attached is my version of the table. OBY is overall brewhouse yield and the efficiency based in the grain’s extract potential. “efficiency” is the efficiency based on the grain weight . The columns headed “w/o considering wort volume increase” match Steve’s calculations where he did not account for the fact that the wort volume in the mash will increase when sugars are dissolved. The columns headed “w/ considering wort volume increase” consider that volume increase and would be the efficiencies that you see if you were to no-sparge a mash and had 100% conversion of the grain’s starches in the mash.

Kai