Need Help Finding Basic Equations

[Krutt]

Hello all!
I'm trying to find some basic equations for calculating things like ABV potential, hydrometer corrections for temp, etc.; and I was hoping you all might be able to help me. My internet is really slow, so I am trying to make something I can use offline in excel.

Here are the equations I am looking for:
-Determine the ABV potential given the starting specific gravity (or BRIX)
-Determine hydrometer offset based upon the test sample temperature (without knowing the hydrometer calibration temp)
-Determine hydrometer offset based upon the test sample temperature with knowing the hydrometer calibration temp
-How to calculate IBU

I was able to find equations to convert BRIX to SG and vice versa, but if there are any other equations you think would be helpful, please let me know.

 

[BrewnWKopperKat]

-Determine the ABV potential given the starting specific gravity (or BRIX)

The Brewers Friend ABV calculator page includes an explanation of the equations it uses.

-How to calculate IBU

The online How to Brew (1e) has information the Tinseth equation.

but if there are any other equations you think would be helpful, please let me know.

Occasionally people post spreadsheets that they have created in the "Brewing Software" forum.

Some web sites (e.g. home brew finds) provide spreadsheets for download.

Finally, there are a couple of open source projects (github).

 

[dmtaylor]

Following are some super simplified rules of thumb for calculating potential ABV and IBUs. These are NOT exact but will be in the right ballpark for most brews.

Potential ABV can easily be figured by knocking the 1.0 off the front of the OG, and then just move the decimal point over to the left one place. For example, you can expect a beer starting at 1.056 to end up with about 5.6% ABV. It's pretty close for most beers. In equation form, this would look like:

Potential ABV = [(OG * 1000) - 1000] / 10

In Brix, you can use the multiplier of 4 to your advantage. The Brix equation is even simpler:

Potential ABV = Brix * 4 / 10 = Brix / 2.5

Regarding IBU estimation, forgive me if I am a little proud of this one. While Tinseth is the most accurate, I have come up with a very simplified approximation that emulates Tinseth for most beers, AND includes whirlpool hop additions, i.e., hop stand. It should come close, within 5-10 of Tinseth, which for many intents & purposes is "good enough". For each hop addition, calculate what follows, then add up the sum:

IBU = oz * AA% * [sqrt(5*Boiltime) + sqrt(2*Whirlpooltime)] / V

Where the times are in minutes, and the V is flameout volume in gallons. Calculate that for each hop addition and add them all together. I dare anyone to try using this and compare against Tinseth in their favorite software.

My IBU calc does get wonky if you use boiltimes greater than ~80 minutes. Probably okay at 90 minutes but it starts to get weirder above that. But, not too many people are going to (1) use my method, much less (2) use it for batches boiled more than 90 minutes. I like this simplified equation as it helps me to respond to questions on the fly when I don’t have brewing software handy to do all the math. I also have an even simpler method called “Remember the Sixes!” that I can share with anyone interested, which can be done in your head as it doesn't involve square-roots... and still every bit as precise.

Sorry I never did figure out or make equations for temperature adjustment of gravity readings. That would be pretty handy. Maybe I can work on that this weekend.

 

[Krutt]

The Brewers Friend ABV calculator page includes an explanation of the equations it uses.


The online How to Brew (1e) has information the Tinseth equation.


Occasionally people post spreadsheets that they have created in the "Brewing Software" forum.

Some web sites (e.g. home brew finds) provide spreadsheets for download.

Finally, there are a couple of open source projects (github).

Thanks for pointing that out. I didn't find anything on finding the potential ABV, but dmtaylor had some good knowledge on it. AND Brewers Friend did do a good job explaining the difference between the basic and alternate ABV calculators; so I grabbed the alternate formula (since I had the basic).

I still have to check out the other locations you mentioned, thanks for the help!

 

[Krutt]

Following are some super simplified rules of thumb for calculating potential ABV and IBUs. These are NOT exact but will be in the right ballpark for most brews.

Potential ABV can easily be figured by knocking the 1.0 off the front of the OG, and then just move the decimal point over to the left one place. For example, you can expect a beer starting at 1.056 to end up with about 5.6% ABV. It's pretty close for most beers. In equation form, this would look like:

Potential ABV = [(OG * 1000) - 1000] / 10

In Brix, you can use the multiplier of 4 to your advantage. The Brix equation is even simpler:

Potential ABV = Brix * 4 / 10 = Brix / 2.5

Regarding IBU estimation, forgive me if I am a little proud of this one. While Tinseth is the most accurate, I have come up with a very simplified approximation that emulates Tinseth for most beers, AND includes whirlpool hop additions, i.e., hop stand. It should come close, within 5-10 of Tinseth, which for many intents & purposes is "good enough". For each hop addition, calculate what follows, then add up the sum:

IBU = oz * AA% * [sqrt(5*Boiltime) + sqrt(2*Whirlpooltime)] / V

Where the times are in minutes, and the V is flameout volume in gallons. Calculate that for each hop addition and add them all together. I dare anyone to try using this and compare against Tinseth in their favorite software.

My IBU calc does get wonky if you use boiltimes greater than ~80 minutes. Probably okay at 90 minutes but it starts to get weirder above that. But, not too many people are going to (1) use my method, much less (2) use it for batches boiled more than 90 minutes. I like this simplified equation as it helps me to respond to questions on the fly when I don’t have brewing software handy to do all the math. I also have an even simpler method called “Remember the Sixes!” that I can share with anyone interested, which can be done in your head as it doesn't involve square-roots... and still every bit as precise.

Sorry I never did figure out or make equations for temperature adjustment of gravity readings. That would be pretty handy. Maybe I can work on that this weekend.

Thanks for all the great info!

 

[brewSJ]

Google "Brew by the Numbers". It's an old Zymurgy article by Michael Hall and has formulas for all the common fermentation-related quantities (including ABV/ABW).

I'm not sure it is possible to do a hydrometer offset without knowing the calibration temperature because it's not a linear shift. If you do know the calibration temperature, the Hall article has a description of how you can figuring out the right offset calculations.

[Edit: fixed the title.]