It’s common when you start brewing to see and hear brewers obsess over what they call their efficiency. I know it’s obvious that they aren’t talking about how organised they are but I want to cover the basics of what your brewing efficiency involves because without knowing this you won’t be able to design a recipe or follow a recipe and hit your target gravity. In other words there will be more or less alcohol than you originally intended.
If you want to formulate your own recipes and to a certain extent follow a recipe then you will want to know your efficiency, in an ideal world everyone would be 100% efficient and but this is impossible even for commercial brewers, although not if you use extract. We will have a look at why in a minute.
For all grain brewers different types of malted grains will only yield a certain amount of extractable sugar, you will be able to find out just how much each variety of malt contains by looking at the specification that each maltster provides or from figures on the internet. When you mash these grains you are attempting to extract as much of these sugars as possible, the amount you extract compared to the amount available is your efficiency and will be expressed as a percentage.
An Efficiency Example
A typical extraction efficiency for all grain brewers will be in the range of 60-80%, if you have an efficiency of 60% and you brew a the same recipe as your friend who has an efficiency of 80% you are going to have less sugar available to the yeast at the end of your brew day. This means you may need to adjust the amount of malt used to achieve the same final gravity as your friend who has 80% efficiency
You can see why commercial brewers would be concerned with getting the maximum efficiency in their brew house because brewing such large volumes means the higher efficiency the less malt will need to be used for each brew. Depending on the size of the brewery this will add up to hundreds or thousands of pounds a year. For the home brewer it doesn’t really matter what your efficiency is, if it’s 75% then increasing it to 80% is going to make little difference to your wallet in an 19 litre brew length.
Working Out You Efficiency
To work out your efficiency requires a bit of trial and error, you will need to know a few things about your recipe. First of all you will need to know the potential extract for each grain in your recipe, then you will be able to determine when brewing 19 litres what the final gravity would be if you managed to extract all these sugars. You can then compare this figure to what you actually achieve when brewing the recipe, a good efficiency to brew your first recipe to is about 75%
It is of course easier to perform your calculations using software but lets take a look at how to work out efficiency using a few simple examples, I think it’s always good to know how to work things out by hand.
First of all lets look at how you would go about adjusting a recipe if you already know your efficiency.
In this simple example let’s say you are brewing a recipe with just two malts; Pale Malt and Crystal Malt. Here are a few key details
Brew Volume: 19 Litres
Target Gravity: 1.050
Recipe Efficiency 75%
Pale Malt: 3.58kg
Crystal Malt: 0.650kg
Now if you already know your efficiency is 82% for instance then you can recalculate the malt you need quite simply, all that you need to do is take each malt and perform the following calculations.
3.58 (weight of pale malt) x 0.75 (percent efficiency as a decimal) = 2.685
2.658kg is the amount needed for 100% efficiency so know we know this we can take this weight and divide it by 82% efficiency to find the weight you need.
2.658 / 0.82 = 3.27kg
So with this calculation if you know your efficiency then you can recalculate the recipe as follows
Brew Volume: 19 litres
Target Gravity: 1.050
Pale Malt = 3.27kg
Crystal Malt = 0.595kg
Now this may seem fairly complex to begin with but bear with me and hopefully it will be clear enough.
To calculate what efficiency you are actually achieving we need to know the potential extract for each type of malt being used. This information is always provided by the maltster making the malt and is also available on the Internet from various sources.
Being British I work in litres and kilograms so when looking at various malts I look for a figure called LDK which stands for litre degrees per kilogram.
You can see an example of this here at Simpsons Malt
Americans tend to measure the potential extract in points per pound per gallon (ppppg) so pale malt for example may be 1.036 ppppg, luckily though we can convert these figures to LDK by multiplying the last 2 digits by 8.3454.
1.036 x 8.3454 = 300 LDK
Let’s work through an example now:
Assuming we brewed the two malt recipe above, got 19 litres and we hit a gravity of 1.057 lets work out our efficiency we achieved at the end of the brew day.
Just to remind you of the recipe:
Pale Malt: 3.58kg
Crystal Malt: 0.650kg
We can calculate efficiency with the following formula Efficiency = Total Gravity of Wort / Total Potential Extract From Grains
The total gravity of the wort in this case is 57 x 19 Litres = 1083
The total potential extract from the grains is as follows:
3.58 (weight of pale malt) x 300 (LDK) = 1074
0.650 (weight of crystal malt) x 292 (LDK) = 189.8
Total Potential of Grains = 1263.8
So your efficiency = 1083/1263.8 = 0.86
There we have it the total efficiency equals 86% lucky you.
There are two types of efficiency people talk about and they are brewhouse efficiency and Mash efficiency. The difference between the two are the brewhouse is the efficiency of the volume and gravity of wort in the fermenter so this would include any wort lost to hops, boiling and so on, mash efficiency is the efficiency of the volume and gravity of wort before boiling.
I don’t really want you to get too bogged down in this for now but as long as you measure your efficiency in the same way consistently for every brew then it doesn’t really matter. You’ll calculate your recipe according to whatever you efficiency is.