EXPERT: Why temperature matters when brewing espresso

Thursday, 28 May, 2020

How Water, Group, and Steam Temperature Can Improve Beverage Consistency

Consistency is critical. Without it, espresso quality will fluctuate, recipes will be hard to refine, and returning customers looking for another one of those “amazing coffees” they drank last time will end up leaving disappointed.

Even small fluctuations in water, group head, and steaming temperatures can cause varying extraction yields and flavour profiles. Here’s why, and how to control them.

How Water and Group Temperature Affect Espresso Consistency and Flavour

We all know that the ideal temperature comes down to the beans’ solubility and that the lighter the beans are roasted, the less soluble they will become and therefore the higher the temperature we should use. However, it’s not as simple as it sounds.

The hotter the grinder, the higher the temperature of the ground coffee. This increases its solubility. Unless your grinder has temperature stability, like the Mythos 2, brewing temperatures should be decreased during peak periods to maintain consistent extraction yields.

What’s more, changing the water temperature affects the flow rate. During pre-infusion, the coffee puck releases gases, mainly carbon dioxide. Some of these gases dissolve in the water, but bubbles are also created that block the water from passing through the puck, decreasing the flow rate.

Gases become less soluble at higher temperatures, which results in more bubbles, further decreasing the flow of water. The flow rate will then increase significantly during the rest of the brew time. This could be a result of channelling as the bubbles may cause small dry patches in the puck that water will bypass.

To avoid these issues, baristas need to pay careful attention not just to the brew recipe but how conditions are changing during the day. This will allow them to adjust the water temperature appropriately.

How Steam Temperature Improves Milk Consistency and Flavour

Small variations in steam temperature can have a big effect on the beverages that you’re serving. Milk that’s too cool will result in poor foam and latte art, while overheated milk will have a thinner, more watery consistency and a potentially disappointing mouthfeel.

The SCA recommends steaming milk to 55–65°C, but the ideal temperature will depend on the milk’s protein and fat content as well as your aim for the beverage. The higher the protein and the lower the fat, the easier it is to create foam at slightly lower temperatures – but the pay-off is a less creamy body.

A dual-boiler machine will mean you can keep the steam wand at a consistent temperature and pressure, ideally slightly lower than the group head. Our T3 technology will also make it easier to set the water, group, and steam temperatures at the individual group heads.

From the team at Nuova Simonelli

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