It’s cold so let’s talk about temperature, in brewing coffee. Ever noticed that it's harder to extract more complex flavours from your filter coffee in colder weather? In this quick post, we explain why that happens and how to avoid an under-extracted brew.
Brewing filter coffee is fraught with variables. The key to making consistently delicious coffee is to control as many of these variables as you can.
Some, are easily controllable like coffee choice, brew method, (immersion, gravity filter, manual pressure) filtering your water and your recipe - the coffee to water ratio which will mostly dictates strength.
Grind size is somewhat controllable. Adjusting your grind to slow down or increase the flow of water through the coffee and increases/decreases surface area of the coffee - resulting in more or less extraction. However, this very much depends on the quality and consistency of your coffee grinder. The finer you grind the more fines you get which can stall your brew by clogging your filter and cause over extraction.
Turbulence is crudely controllable. Think about the water interacting with the coffee from an aggressive or gentle pour, stirring or agitating the coffee with a spoon or pressure, like an Aeropress.
Temperature of water we think of as a choice, we can set the boiler or maybe our kettle at home, or use a thermometer.
In reality we are never brewing anywhere near as hot as we think we are.
Here are some of the ways you lose temperature throughout your brew.
- When brewing coffee using a pourover method, like V60 or Chemex, we use small amounts of water, 50-100ml at a time, usually between 250-500ml in total. That isn’t a lot of thermal mass, so it cools quickly.
- We decant our water into coffee kettles or jugs that are easy to pour carefully from - but in a thin stream that has lots of contact with the air and cools quickly.
- Small, open topped methods like a V60 or Chemex allow heat to escape.
- We don't always preheat our brewing equipment properly.
- We don’t heat our stirring spoon!
We first suspected that temperature was a problem in manual brewing when measuring the taste balance and extraction of an Aeropress when supporting baristas in their practice for the UK Aeropress championships.
We were changing variables and tasting the resulting changes, but struggling to get an increased extraction without bitterness. I suggested checking the temperature, not at the boiler, but in the brewing chamber.
Turns out using 96° water, into a preheated pouring kettle, into an Aeropress gave 86°- 88° water at the start of the brew which decreased with time and turbulence (especially if you, like me, like to stir it up to fully saturate the grounds).
We tried preheating the Aeropress, but plastic doesn’t hold much heat and the hottest we got was 91°. That was pouring 98° water directly into the brew chamber with minimal stirring.
For reference SCA guidelines state to use 93° +/- 3° water for brewing filter coffee
A variance of 8 to 10 degrees between the temperature of your kettle, and the temperature of your coffee as it brews has a huge impact on your extraction.
The temptation in these scenarios is to grind more finely to extract more flavour from the coffee but the risk here is that you go too fine, and the fines clog your brew, resulting in over-extracted, bitter tasting coffee. (No thanks).
Actually, taking some steps to better control temperature during your brew can be more effective.
These tips have helped us brew fuller, tastier coffees in cold environments without having to grind finer and risk clogging up our brews and over-extracting the coffee.
Golden rules for brewing filter coffee in cold weather
- Preheat the hell into your brewing equipment. That's cups, cafetieres, kettles and spoons.
- Use hotter water than you think you can.
- Get the coffee hot and wet, keep it that way throughout your brew.
All that reading made you thirsty?
Well done, you've made it to the end of our filter brew guide for cold weather. If all that reading has left you craving a coffee, we've got some outstanding new filter coffees available on the website now.