Author Topic: Final Gravity Design Calculations  (Read 1061 times)

Offline jpsantacruz

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Final Gravity Design Calculations
« on: February 26, 2017, 05:00:25 PM »
I'm new to Beersmith, tried putting in a partial mash recipe that have already brewed. Everything looks good, except for the final gravity number in the design tab of the program.  I'm starting at 1.050OG, and pitching from a 1.6L starter, on a stir plate, using both Wyeast 3711 + WL565.  The starter tab is optimistic about cell count, but either underestmates the attenuation, or doesn't carry it back to the design tab.  In real life, I got 1.002FG, but the program suggests that I'm designing for 1.015FG, which I am not.  The whole idea is that this beer is supposed to be super dry, (and carbonated at 3.2 volumes of CO2.)  It looked like attenuation was grayed out, and I'm not sure how I would know to input specific percentages from intuition.

As a first time user, I'm sure that I'm missing something.  I want to understand this part of the program, because this isn't the last time I'm going to try to design a low Final Gravity beer. 


Offline GigaFemto

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Re: Final Gravity Design Calculations
« Reply #1 on: March 02, 2017, 11:49:25 AM »
Attenuation is a calculated value, not a direct input, which is why it is grayed out. BeerSmith calculates the attenuation based on the yeast information and the mash temperature. For extract it must use some default fermentability number. It then uses the estimated attenuation to calculate the FG. If you are absolutely sure you know your attenuation and want BeerSmith to use that, then you could edit the yeast entry. I would leave the original untouched and make a copy of the yeast with your information. There are fields for maximum and minimum attenuation. If you make them both the same. then BeerSmith uses that as the starting attenuation and adjusts the attenuation up or down based on the mash temperature. You could iterate a few times until you get the predicted attenuation you want. That may or may not work for a different recipe.

BeerSmith is good at giving reasonable estimates for cases where you have no idea what to expect, but it doesn't always give the exact correct result for a process that you have precisely dialed in. There is enough flexibility that in those cases you can usually go in and force it to give the answer you want.  For equipment profiles getting it right once will usually mean you get it right in the future, but I am not sure that will work as well with yeast attenuation.

-GF

Offline jpsantacruz

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Re: Final Gravity Design Calculations
« Reply #2 on: March 15, 2017, 02:35:18 PM »
I guess your suggestion is to monitor my process until I'm able to use the the yeast input to force BeerSmith to back into a known correct answer.  At that point, BeerSmith isn't really helping me with that aspect of the design.  I felt that the difference between 1.015 and 1.002 was not minor, relative to a dry Saison.  The IBU and OG calculations are still helpful, I suppose.


Offline GigaFemto

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Re: Final Gravity Design Calculations
« Reply #3 on: March 15, 2017, 08:44:07 PM »
You're right that playing around with the inputs to get BeerSmith to predict the result you want to get is a bit perverse. If you were only using the software for that one purpose it would be a waste of time to do this, but BeerSmith does a lot of things and it may be that you find enough of the features to be useful that they make up for having to force it in one area. The database of grain, hops and yeast with all their characteristics is something that I find very valuable even if I can do the OG and IBU calculations myself.

 

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