Depending what coffee machine you own, or what brew device you use, temperature can be a variable you can control to help achieve the cup you are after.
Brew temperature can have a huge effect on the taste of your coffee. It is well known that increased temperatures will increase extraction, this is because most particles in coffee are more soluble at higher temperatures.
However it is not just as simple as that, coffee can be extracted to the exact same rate at varying temperatures, yet have completely different taste profiles. This happens because individual compounds in coffee having varying optimum extraction temperatures. The Coffee Brewing Handbook written by Ted Lingle, preformed a study on this, which can help us understand why the flavours change so drastically. Our aim here is to use this information to help us use brew temperature to tweak the final flavours we want in a cup.
The brew temperature has the following effects on these three key components:
As demonstrated in the graph above, even small 1 degree increments in brew temperature can change not only the extraction rate but the mix of sugars and acids that are in the cup.
Citric Acid: A key acid found in coffee, responsible for adding citrus tasting notes like lemon, lime, grapefruit, orange ect.
Malic Acid: A key acid found in coffee, responsible for fruity tangs and complexity in coffee. Adding tastes of green apple, pear and other fruits.
Sucrose: The main form of sugar found in coffee beans (making up more than 90% of the total sugar content in the beans). Responsible for sweetness and adds to body.
The aim in a well extracted coffee recipe is to find a balance of these components as well as others, to create a taste experience where all elements work in harmony.
Referring back to the chart above, optimum brew temp sits around 93-94 degrees for most coffees. This is the temp that I would recommend setting an espresso machine as a general rule, only differ from this temp if you want to fine tune and manipulate the extraction to bring forward different flavours in the espresso.
If you are working with a lighter roast coffee and you would like to bring out more sweetness, body and increase the extraction, then try working with a brew temp 1-2c higher. This will help bring more sugars into the cup, mellowing out the acidity while also increasing the overall extraction. This can be beneficial with lighter roast coffee as they tend to have a higher acidity and be harder to extract due to their density.
On the other end of the spectrum if working with a dark roast coffee that is imparting a high level of bitterness, overpowering body and lacking in complexity from low levels of acidity, then bringing the temperature down by 1-2c can help overcome these issues.
In a high volume commercial setting bringing brew temperature down slightly can help assist in stabilising extraction consistency. During peak trading times coffee grinders work overtime and can heat the coffee grounds up, effecting extraction rates. This can be counteracted by dropping brew temperature by 0.5-1c during these times, maintaining a more consistent coffee.
Recent experiments have demonstrated that brew temperature in espresso can also have a small effect on flow rate at different stages of the shot. With increased temperature, the start of the shot tends to flow slower and speed up more towards the end of the shot. The theory behind this, CO2 reacts with the higher temperature water increasing resistance at the start of the shot, locking the coffee particles in place, similar to how low flow pre-infusion works. As the gasses disperse and particles are locked into place reducing fines mitigation, the flow rate increases as resistance reduces in the second half of the shot. It should be noted that the change is fairly minimal and more an interesting side effect to take note of.
Keep in mind that using the technique of changing brew temperature should be one of the last methods used to manipulate the extraction. As always with coffee, start simple and consistent, fix as many variables as possible when dialling in a coffee. Usually adjusting grind size, an even distribution and setting a ratio/recipe that works for the the coffee/brew method you are trying to achieve will result in a great cup of coffee. Methods like these mentioned above will help you fine tune difficult or obscure coffee’s that may sit outside the norm.
Small changes are all that’s needed, usually changing the temperature by 1 degree at a time is enough. If you want to to experience and test the differences in flavour vs. brew temperature, try extracting three espressos at 91c, 93c, and 95c. Taste them all and note the different tasting notes, body and overall impression of the coffee. Brew temperature is crucial with manual brews like the v60, chemex, and others, try brewing three pour overs at temps 92c, 95c, 98c and taste the final cups, they will taste very different.
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