There are three roast parameters that influence the calibration of the coffee and its final cup attributes. We cover all three in our Ultimate Coffee Roasting Course. One of these parameters is the Agtron colour of the coffee.
Agtron colour is the measurement of how light or how dark a roast is. It has a linear correlation with the required calibration style. We define light, medium and dark roasts as
a) Light Roast - above Agtron 75,
b) Medium Roast - between Agtron 50 - 75
c) Dark Roast - below agtron 50 respectively.
These are based on agtron measurements of finely ground coffee, not whole bean.
Calibrating to color
Assuming standard brew ratios are 1:2 (espresso) and 1:18 (filter), darker roasts generally perform best with shorter brew ratios/higher dose, coarser grind sizes and shorter contact time. The darker the roast, the bigger the impact. This explains why ristrettos used to be so popular since majority of espresso roasts lean towards the darker end of the spectrum in the past.
Conversely, lighter roasts generally perform better using longer brew ratios/lower dose, finer grind sizes and longer contact time. The lighter the roast, the bigger the impact. The reason we use the term “generally” is because the correlation between colour and calibration requirements are loose and there are other additional factors which influence the extraction of the coffee. Within a single colour category, there can still exist a deviation in terms of calibration parameters.
For example, a medium roast (agtron 65) can be made to taste good at both a slightly longer or shorter ratio than the standard. (e.g. 1:1.8 to 1:2.2 for espresso)
So, colour is not a very accurate determinant but can provide a good starting point. Now let’s discuss how this impacts the final cup attributes.
Results in the cup
In general, a darker roast should bring about lower acidity and higher bitterness. This helps to balance out coffees more easily and create sweeter coffees. Saltiness is generally a result of under-extraction or under-developed roasts so it should not be present in a properly executed dark roast.
By its nature, darker roasts will tend towards riper flavours with a strong flavour structure and intensity. This comes at the cost of cleanliness and clarity in the cup as there tends to be more pyrolysis and melanoidins present in the coffee. At the same time, these same brew colloids that impact cleanliness also adds to a heavier body weight and fuller mouthfeel.
However, as we’ve noted, darker roasts perform better using coarser grind sizes, smaller brew ratios/higher doses with shorter contact times. This runs in contrast to the nature of the roast. Coarser grind sizes and shorter ratios and contact times all serve to extract less of a coffee and in turn create thinner, higher acidity coffees. We’ve noticed this same pattern in calibrating lighter roasted coffees as well. The calibration settings are inversely related to the roast style.
Lighter roasts generally bring about higher acidity and lower bitterness. This creates brighter and less sweet coffees with a chance of saltiness if incorrectly executed. The benefits of a lighter roast are the increased cleanliness and clarity in the cup. There can still be good flavour ripeness but overall structure will be weaker and breaks down as the cup cools. The reduced pyrolysis and melanoidins present mean that there tends to be a lighter body weight and thinner mouthfeel.
But the calibration settings to showcase this roast colour best requires finer grind sizes, higher brew ratios/ smaller dose and longer contact times. These settings are meant to help extract more of a coffee and create heavier, more bitter-sweet coffees. Completely opposite to what the roast is meant to present.
Ultimately, there seems to be a theme whereby calibration settings are inversely related with roast. This is meant to help bring about balance in the final cup. A light roast brewed using coarse grinds and short ratios would be immensely sour and not taste very good.
Applying it to your work
As a roaster, if you are roasting towards a particular colour, it would be prudent to communicate with your baristas what would be the best direction for adjusting their calibration settings to match your roast colour. Or if you are trying to match their calibration settings, then you would know which direction to adjust your roast to create a well-balanced cup.
If you are a barista, talk to your roaster. Find out the direction that they are going with the coffee so that you better understand how to calibrate in line with the coffee's roast parameters. We also covered how coffee roasting affects your brew recipe in an earlier article. You will learn how to adapt to different roast styles much better if you understand the ingredient you are dealing with.
At the end of the day, even though the calibration settings are meant to run counter to the roast colour, the roast still plays the major role in deciding the final taste attributes of a cup. The calibration settings are there to balance and smoothen out any rough edges in the roast. If the coffee still tastes wrong despite your best efforts, you might want to check out what makes your coffee bitter and how to fix it.
Colour no doubt plays an important role in affecting the calibration of a coffee, but it is not the most important factor. There are actually TWO additional factors that plays a huge part in influencing the coffee calibration. We cover these two factors in our Ultimate Coffee Roasting Course if you want to upgrade your coffee skills. If not, you can also enjoy some of our latest coffee releases over at our online shop. Stay safe!