Beersmith vs. Online Calcs

[LeftyMcGee]

I downloaded Beersmith and have been trying it out. I have noticed the amount of hops needed to meet a specific style is dependent on the boil volume. I have formulated the same recipe on Beersmith, TastyBrew's Calc & BeerCalculus. When I change the boil volume on each to 2 gallons, they differ in the amount of hops required to meet a specific IBU. On an APA I was designing, Beersmith required 1/2oz (bittering hops / 60min) more than BeerCalculus and BeerCalculus required 1/2oz more than TastyBrew. It seemed like TastyBrew's recipe calc didn't even change the calculated IBU's when I changed my boil volume to 2 gallons.

I am new to homebrewing, but it seems to me that calculating IBUs is very mathematical and each of these resources should come up with fairly similar numbers. They all seemed to calculate the OG and FG within a fairly close range.

I was wondering if anyone could shed some light on why these three resources differ in their calculations. It seems like 1/2oz to 1oz difference in a bittering hop with 12.2%AA would make a pretty substantial difference in the taste of the brew.

 

[Yuri_Rage]

You're right in that calculating IBUs is simply math. Unfortunately, it's not simple math. Quantifying bitterness is actually extremely difficult, and there have been many attempts at finding an algorithm that fits. There are at least three different algorithms (Tinseth, Rager, Garetz) commonly used in brewing, and each of them will result in a slightly different answer.

I use Tinseth (set in BeerSmith as the default algorithm), as I've heard that it's the most accurate for small batch brewing. Regardless of the accuracy, I find that I get expected and repeatable results by sticking to a single method.

 

[LeftyMcGee]

That makes sense. I did not realize that there were 3 different accepted algorithms for determining bitterness.

I am not sure what BeerCalculus uses, but I looked at TastyBrew and they also use Tinseth. I just tried their bitterness calculator and it was in the same range as Beersmith (about .4 IBU difference with same OG), but their recipe calculator is giving me way different IBUs. I used the same OG in the recipe and bitterness calculators. Guess their recipe calc is just off when it comes to determining bitterness.

Anyway, thanks for the info!

 

[Coastarine]

I have heard tinseth is best for small batch but full boil. If you're boiling less than the full volume of the batch, I've heard rager is better. Everyone who gets beersmith goes through the same thing, but i really love the program.