How do you calculate beer colour? This is a key consideration especially when you are adding coloured malt into your home brew recipes. If you are not to over shoot and add too much coloured malt to your grist recipe it is useful to have a method to calculate the colour contribution of a certain quantity of malt. It is also useful to have an idea of the likely end colour of your beer.
Therefore it is a very important consideration for a home brewer. Therefore how do you calculate beer colour?
Working out the colour of your beer should be easy and in some respects it is. However, before we discover how to calculate the colour of beer it is perhaps worth considering the history of colour measurement in beer, which is convoluted to say the least and just a little bit subjective.
The first quantitative method for measuring colour in beer was devised by Joseph William Lovibond in Greenwich in 1893. The method he developed involved comparing beer samples to standardised coloured glass discs.
A bit like the paint colour charts you get from you DIY shop the Lovibond method involved matching your beer sample against various glass discs that had a known colour value. The glass disc that best corresponded to the colour of the beer therefore gave the colour value of the beer.
The Lovibond method became the standard method for determining colour until 1950 when L.R. Bishop proposed the use of a revised set of coloured glass slides. Bishop’s revised system of colour determination was adopted as the standard method for beer colour analysis by the European Brewing Congress (EBC) and therefore the standard method of analysis for European brewers.
However, because this is a visual method, that is a human has to decide which colour slide best matches the colour of the beer, the method is highly subjective. This means that the colour analysis can be quite inconsistent from one lab technician to another and certainly between different laboratories.
To take account of the inconsistencies of this visual method US brewers use the Standard Reference Method (SRM), which rather than using a human to judge the colour uses a spectrophotometer instead to gain a value of beer colour.
To perform this method the beer sample is placed in a glass cuvette which goes into the spectrophotometer. The absorbance of the sample is then measured at 430 nm and the colour calculated taking into account the path length of the cuvette and any dilution factors that may have been used on the original sample. The EBC have also adopted a spectrophotometric method but because of slight method differences the EBC colour is roughly twice the SRM colour. To be precise the EBC colour is 1.97 times the SRM colour. Therefore a colour of 8 on the SRM is:
EBC colour = 1.97 x SRM
EBC colour = 1.97 x 8
EBC colour = 15.76
However, really I don’t think that there is much need to go to this level of precision.
There are still issues involved with the spectrophotometric methods and the main issue is if the beer has a slight haze or turbidity issue. If it does have a haze the colour reading can be impacted.
This is more important when it comes to the analysis of malt for its colour. When determining malt colour the malt sample is mashed and a wort produced. It is the wort which is then analysed for colour. The problem is that very often the wort will be hazy which impacts on the assessment of colour.
To account for this in the EBC method there is a requirement to measure the sample in a spectrophotometer at 700 nm to see if there is a haze. Generally if the absorbance value at 700 nm is greater than 0.02 the beer sample is deemed to have a slight haze. If the sample does have a haze it therefore needs to be either filtered or centrifuged to remove the haze.
As you can see there are some issues with trying to measure and understand the colour of the beer that we want to make. This is especially true when it comes to the measurement of hue. The subtle variations in the hue that the human eye can see, which give us copper red or chestnut brown beers for example, cannot be easily translated into a single number. I would therefore suggest that when you calculate the colour of your beer this can only be used as guidance for the rough level of colour. However, by experimenting with the colour values that you get and the type of coloured malts that you use in your recipes you will quickly gain experience as to what colour value you are likely to achieve.
Now having gone through some of the complications of analysing colour it is worth considering our original question – How do you calculate beer colour?
For this calculation you can use either the EBC colour or the Lovibond colour of the malts that you want to use. The colour values of the malt that you are using should be clearly stated on the certificate of analysis that you asked for when you purchased the malt.
To estimate the colour of your beer you need to know the colour value of the malt that you will be using, the weight of malt and the volume of beer you want to make. Using this we can work out the Malt Colour Value or MCU.
Therefore going back to our original simple recipe where we were making 25 litres of beer at 5% abv using 100% ale malt.
The recipe calls for 4.6 kg of ale malt which has a colour of 7 EBC or approximately 3.5 Lovibond.
The calculation we use to work out the colour value for our beer is:
MCU = weight of malt (in lbs) x malt colour (in lovibond) / volume (in gallons)
To convert our recipe from kg and litres into US gallons and lbs we use the following conversion factors:
1 litre = 0.264172 US gallons
1 kg = 2.20462 lbs.
25 litres = 6.6 gallons
4.6 kg = 10.1 lbs
Therefore the MCU will be:
MCU = (10.1 x 3.5)/6.6
MCU = 5.3
To calculate this as an EBC colour you need to multiply the MCU by 1.97. Therefore an EBC colour for this recipe will be:
EBC colour = 5.3 x 1.97
EBC colour = 10.4
There you have it that is how we calculate the potential colour of beer. However, sadly it is not quite as simple as that.
What happens if we want to use different types of malt in our recipes and also use coloured malt? How do you calculate the colour of beer for a more complex recipe?
In this case we have to work out the individual MCU for each malt type and then add them together.
Let’s take a look at the more complicated recipe we calculated which used ale malt, torrefied wheat and crystal malt.
If you remember for this recipe we required:
Ale malt = 3.9 kg (8.6 lbs)
Torrefied wheat = 0.5 kg (1.1 lbs)
Crystal malt = 0.25 kg (0.5 lbs)
For these individual ingredients the colour values are:
Ale malt = 3.5 lovibond
Torrefied wheat = 2 lovibond
Crystal malt = 140 lovibond
Therefore to calculate the MCU for each of these components we use the calculation above:
MCU = weight of malt (in lbs) x malt colour (in lovibond) / volume (in gallons)
For the ale malt this will therefore be:
Ale malt MCU = (8.6 x 3.5) / 6.6
Ale malt MCU = 4.6
For the crystal malt this will therefore be:
Crystal malt MCU = (0.55 x 140) / 6.6
Crystal malt MCU = 11.7
For the torrefied wheat this will therefore be:
Torrefied wheat MCU = (1.1 x 2) / 6.6
Torrefied wheat MCU = 0.33
The total MCU for the recipe is therefore:
Total MCU = 4.6 + 11.7 + 0.33
Total MCU = 16.6 Lovibond
Or as an EBC colour this will be:
EBC colour = 16.6 x 1.97
EBC colour = 32.8
Hopefully you have followed the calculation this far and you are happy with the colour value calculated.
There is one last thing to take into consideration and that is the simple issue that light absorbance is not linear so when we are measuring the colour with a spectrophotometer this need to be taken into account. The calculated value above would be fine if the colour of the beer was between 1 – 5 units on the SRM. However, between 6 – 8 SRM the estimate of colour starts to breakdown and we need to adjust for this. We therefore need to apply the Morey equation which is below:
Colour = 1.4922 x (MCU^0.6859)
Therefore if we insert our colour of 16.6 into this equation we get the following:
Colour = 1.4922 x (16.6^0.6859)
Colour = 1.4922 x 6.86
Colour = 10.2
And as an EBC colour we again must multiply by 1.97.
EBC colour = 10.2 x 1.97
EBC colour = 20.1
There we have it a simple, ok not so simple, calculation of how to measure the potential colour of your beer. Remember this value comes with some caveats which are:
- The colour methods are not fantastic
- The colour does not take into account the subjective quality of colour hue
- The brewing process has an impact on colour. For example when you boil your wort the colour is likely to darken due to interactions between proteins and sugars to give highly coloured compounds.
Now for those of you who have an aversion to calculations at the end of this series of articles we have a downloadable spreadsheet which will do all the calculations for you.
Next up we will consider how to calculate the quantity of hops required to achieve a particular bitterness in your finished beer.