The Beginner Brewer: 2 Calculations to Improve your Homebrew

Friday, 27 September 2013

2 Calculations to Improve your Homebrew

Most home brewers I know find brewing beer at home to be one of the most relaxing hobbies out there. The world disappears and work-related stress blow off along with the DMS wafting away from a good, rolling boil.

So if math feels like work to you, introducing calculations into homebrewing can seem like a pain. But have no fear--the following two calculations are simple and best of all--will help you to improve your brews and gain greater control over the final product!
Time to Calculate!

Calculation #1: Attenuation

Attenuation is the percentage of fermentables that were converted due to fermentation. Confused yet?

No need to be: It's actually quite simple. After you've pitched yeast into your wort, these marvelous little organisms start to convert simple sugars like maltose and dextrose into alcohol and CO2, neither of which are sweet to the taste.

More complex sugars like lactose are not converted in this way, and contribute their sweetness directly to the final beer. Also, not all the fermentable sugars are converted, thus contributing their sweetness to the final beer as well. Attenuation is determined by a number of factors, chief amongst these being the strain of yeast you used and the composition of your wort. 

Some yeast strains, like certain Saisson yeasts, have very high attenuating properties, which means that they will aggressively convert fermentable sugars until almost none are left. This results in a less sweet, drier mouthfeel in the final product. Other strains, like those used in traditional British Ales, are less attenuating, and will leave far more sugars unconverted, resulting in a full bodied, sweeter mouthfeel.

Of course, the actual percentage of fermentable sugars in your wort also plays an important role in attenuation, and that's why all grain brewers are often concerned about their mash temperatures, since these influence the percentage of fermentable sugars created during the mash.

Calculating attenuation is an after-the-fact deal. Once you've measured your Original Gravity and Final Gravity, you can calculate the Attenuation, thus:


So, as an example, if your beer had an OG of 1.050 and a FG of 1.011, your calculation will be:
(50-11) / 50 = 0.78, or 78% attenuation

Becoming familiar with the different attenuation rates of different strains of yeast, as moderated by your beer recipe and things like mash temperatures, is a good way of becoming a more consistent homebrewer!

Calculation #2: Bitterness Ratio

I can't over-emphasize the utility of calculating bitterness ratios. Once you start targeting specific bitterness
ratios with your brewing, you'll really get to grips with producing a wide variety of taste profiles in your homebrew, as well as mastering the multitude of beer styles available to the home brewer.

Bitterness Ratio: It's about Balance
Bitterness Ratio is a two-step calculation, as follows:

Step 1

First, divide the total IBU of the beer by the Original Gravity:

Step 2

Then, plug that result, which we'll call BR1, into this calculation:


So, let's imagine that our previous example beer (the one we calculated the attenuation for), has a total of 30 IBUs. It's OG is 1.050 and FG is 1.011. We've already calculated the attenuation, and that's come to 0.78.

Now let's calculate BR1: 30/50 = 0.600. (Note that for this calculation, we use only the numbers after the decimal for OG and FG).

We are now ready to calculate the Bitterness Ratio of this beer:
0.600 x (1 + (0.78 - 0.7655) = 0.608, which is the Bitterness Ratio of this beer.

If you use a software package like Beersmith, you'll soon realize that different beer styles have different bitterness ratio ranges, and so if you really want to nail a particular style of beer, knowing how to calculate bitterness ratios is a must!

For more details on Bitterness Ratio, I recommend the excellent Mad Alchemist beer blog. 

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{Picture credit: abacus by Anssi Koskinen}

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