Filter brewing
Preheating a brewer
Small brews lose a surprising amount of heat into cold ceramic, metal and glass. Warming everything first costs ten seconds.
- Skill level
- Beginner
- How long it takes
- Ten seconds
- Equipment needed
- Pour-over dripper
- Steps
- 3
In short
Preheating means warming the brewer, and usually the cup or server, with hot water before brewing. A cold object in contact with brewing water takes heat from it, so the coffee extracts at a lower temperature than the kettle would suggest.
How much that matters depends on how heavy the brewer is, what it is made of and how small the brew is. For some setups it is the difference between a sour cup and a good one. For others it makes no detectable difference.
Where the heat goes
CoffeeHQ explanation
Hot water poured into a cold vessel shares its heat with the vessel until the two are at the same temperature. The heavier the vessel and the less water there is, the bigger the drop. A thick ceramic dripper or a large glass press holds a lot of material to warm up; a thin plastic dripper holds very little.
Cooler water extracts less in the same time. So a brew that has lost heat to a cold brewer tends toward the thin and sour that mark under-extraction, most of all with light roasts, which are already the hardest to extract.
Which brewers gain the most from it
Tendency, not a guarantee
| Variable | Typical range | What moving it does |
|---|---|---|
| Ceramic or glass pour-over dripper | Clear benefit | Heavy, starts cold, and a small volume of water passes through it. |
| Plastic pour-over dripper | Little benefit | Takes up very little heat. The filter rinse is enough. |
| French press | Worthwhile | A cold glass or steel jug cools the whole brew for the length of the steep. |
| Espresso portafilter and cups | Clear benefit | A cold portafilter and a cold cup both cool a very small volume of liquid. |
| Moka pot and cezve | Not applicable | The brewer is on the heat throughout. |
| Cold brew | Not applicable | There is no heat to keep. |
Relative tendencies, not measurements. The size of the effect depends on the brewer, the batch and the room, and a larger brew is always less affected than a small one.
How to preheat, by brewer
Widely documented
- Pour-over. Rinse the paper filter in place with plenty of hot water. That wets the paper and heats the dripper and server together. Empty the server before brewing.
- French press and other immersion jugs. Fill a third of the way with hot water, swirl, leave for half a minute and pour it away. Warm the plunger at the same time.
- Espresso machine. Leave the portafilter locked into the group while the machine heats, so it reaches working temperature with it. Warm cups on the machine's tray or with hot water.
- Cups and mugs. Fill with hot water while the coffee brews and empty just before pouring. A thick cold mug takes a noticeable amount of heat from a small drink.
Find out whether it matters for your setup
CoffeeHQ explanation
Preheated against cold
- Change
- Brew the same recipe twice: once with the brewer and cup preheated, once with both left cold.
- Keep the same
- Coffee, dose, grind, water amount, kettle temperature and timing. Brew one straight after the other.
- What to notice
- Whether the cold-brewer cup tastes sharper, thinner or less sweet. If you cannot tell them apart, preheating is optional for that brewer.
When preheating is wasted effort
CoffeeHQ explanation
With a lightweight plastic brewer, a large batch, or an automatic machine that heats its own parts, the heat lost to the equipment is a small share of the total. Dark roasts are also more forgiving of a slightly cooler brew, and some people prefer them brewed cooler.
Preheating is a way to remove a variable, not a way to add quality. If your brewer is warm already, or light enough not to matter, the same effect can come from using slightly hotter water. What counts is that you do the same thing each time, so that a change in the cup can be traced to something you meant to change.
What to do next
- Rinsing a paper filter — For pour-over, the rinse and the preheat are the same pour of water.
- Water temperature — How temperature affects extraction and how much it is worth adjusting.
- Brewing variable explorer — See what a cooler or hotter brew tends to do, method by method.
- Coffee too sour — A cold brewer is one of several causes of a sour, thin cup.
- Become a barista — A structured programme from dose and grind through milk, drinks and maintenance.
Why it works this way
A 250 ml brew has very little thermal mass, and a cold dripper, carafe or cup has quite a lot. The result is a brew that starts at the temperature you chose and finishes several degrees below it, which is commonly blamed for a sour, thin cup. It matters most for small pour-over brews, for manual espresso devices, and for any drink served in a cold cup — including a flat white, where a cold cup can take a noticeable amount of heat out of a small volume of milk.
What you need
Required
Helpful, not essential
How to do it
Run hot water through the brewer and into the serving vessel.
Combines with rinsing the paper if you are using one.
Discard the water immediately before brewing.
Warm, not wet, is the goal.
Warm cups for espresso and milk drinks too.
A cold cup is the most common reason a correctly steamed flat white arrives lukewarm.
How to tell it worked
A brew that tastes the same at the last sip as at the first, and a milk drink that stays comfortable to drink for longer.
If it did not work
What you saw, what to change, and why the change works.
Coffee tastes thin and sour despite a reasonable recipe
Change: Preheat everything and brew again before changing the grind.
A cold brewer is a common suspect. In the one controlled tasting read, a few degrees of brew temperature made little difference once strength and extraction were matched, so treat this as something to rule out.
Common mistakes
Preheating and then leaving everything to cool while grinding
The benefit is gone by the time brewing starts.
Instead: Preheat last, immediately before brewing.
Diagnose a specific problem
The science behind it
- Water temperature
Hot coffee is usually brewed with water just off the boil; in the one controlled test read, a few degrees made little difference.