How important is temperature variation for extracting espresso, and what does it do? Hugh Kelly writes about the relationship between temperature and espresso and how to measure it.
The role of temperature on espresso is a seemingly well understood variable by some in the coffee industry. But for others it can be difficult to know when brew temperature should be considered as an extraction variable.
First lets break down some key considerations to understand when approaching brew temperature in your espresso machine.
Number one is having a basic understanding of what machine you are using and whether it displays a true applied brewing water at the head from machine to machine or whether its an approximation measured further back in the machine.
If you have never seen a PID control, it is essentially a box that attempts to control machine temperature based on the readings it picks up from a temperature probe. The temperature probe can be located in different points of the espresso machine depending on what the manufacturer chooses to measure – some machines place their probes much closer to the output of the brew head, whereas others measure boiler temperature while some are now measuring the slurry temperature from just above the shower screen in the group head itself.
If the measurement is being taken from the boiler than the temperature of the water coming out is almost definitely not the same temperature. In this case in order to achieve a 93.5-94 degree water output you may need to set the PID to more like 96-97 degrees accounting for any loss in temperature in the lines. Be wary of under bench machines where you may need to set temperatures quite different for each head to account for different lengths of line running from the boiler underneath to the group head above.
Other machines have their temperature readings calibrated in the factory using a scace, which is a handle with a probe that can measure water temperature output. What is important to understand here is this also doesn’t necessarily mean your brewing water is what the machine is telling you it is.
Machines being shipped from overseas can see slight movement or even malfunction of temperature probes meaning if machine distributors or technicians aren’t checking machines coming in properly, temperature can run different from machine to machine.
The next consideration involves the correct operation of a scace. There is a specific way to do this properly but not all people follow protocol leading to inconsistent readings and incorrect machine calibration. Technically, a scace handle must be inserted into a hot group head and left for 1 hour to reach temperature equilibrium and only then will temperature be accurately measured by the probe (however 30 minutes is usually fine).
Next is the quality of multimeter being used. Some meters are simply inaccurate showing 3 degrees difference off the same scace between meters. I don’t work for or are affiliated with any manufacturers, but fluke multimeters seem to be pretty reliable but should be sent back for calibration at minimum every year.
From testing machinery i’ve learned there are only a handful of manufacturers that are precise with their temperature stability so speaking with them or your tech on the hows and whys can help you understand if you can simply set your machine to a temperature based on what others have said they brew at or need to start elsewhere.
So, let’s dive into the barista side of the equation. Most espresso coffee should be brewed with 90-95 degrees celsius brewing water. But where should you start?
Brewing coffee within this temperature range will not significantly affect extraction yield. There may be 1-1.25% increase within this 5 degree range but when you are narrowing in on brew temperature we will be talking in 0.5 degree increments and a small change in grind or dose will affect extraction yield far more.
Where brew temperature plays a far bigger role is with the compounds you extract from your coffee. A good way to think of this is that higher temperature has the potential of extracting more. This includes more acids which can include fruit acids and also potentially astringency; this also means more sweetness; and also potentially more dry distillates which can include bitter and drying compounds. Depending on what your coffee has to give, increasing temperature can be a good or bad thing.
Brewing with lower temperature brew water (under 90) has been used by some to ‘increase juiciness and acidity’ in the brew. However the level of acid is actually less than coffees brewed in the 90’s and instead sweet and heavy compounds have dropped in comparison with acid.
Next is considering your roast profile. Darker roasted coffee will generally need a lower temperature 90-92.5 degree water as with higher temperatures we extract more of the heavy ashy and harsh roast compounds from the coffee.
Similarly, in very light roasted coffee it can be more difficult to find compounds contributing to sweetness and body and we are not trying to avoid heavy roast elements because there is usually less of these in lighter coffee. Extracting these coffees at 90-92.5 degrees can yield nutty, savoury, underdeveloped flavours with a very sour acidity. Starting at 93.5 degrees is a good starting point and increase temperature if there is a general tendency of drying and sour acidity.
For medium roasted coffees also start at 93.5 degrees. Increasing the temperature may find more sweetness and texture but it also may find more bitterness, roughness in texture and also astringency (look at the back palate). Lower temperatures may reduce these qualities but also fail to develop enough sweetness to balance acidity giving a dry aftertaste. These changes in taste come with as little as 0.5 degree changes on the espresso machine thats because the effect of every change is amplified under pressure.
What is extremely important to understand is that temperature adjustments are a final tweak once you have general brew recipes close to where they need to be. Often espresso and milk based coffees are roasted differently which may require slightly different temperatures to get the best out of them. Therefore having a more generalised temperature set point and working on other brew variables first is usually the best way to work.
Having machines with dedicated brew boilers and temperature control for each head can allow for more flexibility but if you are working from a single brew boiler, a more generalised approach is best. Before considering temperature as a variable understand your machinery, ensure pressure is correct and not fluctuating and taste regularly.