Why Coffee Tastes Better as It Cools | Jasper Coffee Melbourne

You put your coffee down for one email. It became five. By the time you look up, the coffee has cooled off considerably, much like your enthusiasm for the inbox. Take a sip anyway, though, and something odd has happened: it tastes sweeter, fruitier and more interesting than it did when it was hot. You're not imagining it. We've been roasting coffee in Melbourne since 1989, from our first days on Smith Street in Collingwood, and this is one of our favourite bits of coffee science.

Your tongue has a fire alarm

Here's a fact worth bringing out at dinner parties: very hot coffee and a fresh chilli set off the same alarm in your mouth.

Scattered through the tongue and mouth are nerve endings carrying a sensor called TRPV1. It's the one that makes chilli burn, and it also switches on when things get hotter than about 43°C, the point where warmth starts to tip over into 'careful now'. Its job isn't flavour at all. Its job is to tell your brain that something might be about to hurt.

Most people drink black coffee at 58°C to 66°C, according to a UC Davis Coffee Center study that served more than 3,000 cups to find out. That's well above the alarm's trigger point, so for the first few sips your brain is mostly asking one question: is this too hot? Flavour has to wait in the queue.

Researchers also suspect heat simply hogs our attention, and that taste in general fades once things get hot enough. Either way, the scalding first sip is not your coffee at its most talkative.

Sweetness likes it warm, not hot

When something sweet lands on your tongue, it sets off a chain reaction in your taste cells that ends with a tiny gate, called TRPM5, swinging open and sending the 'sweet' message to your brain. In 2005, physiologists at the University of Leuven in Belgium found that this gate is rather particular about temperature: the warmer it gets, up to around body temperature, the more readily it opens. In mice, sweet responses climbed dramatically as a drink was warmed from 15°C to 37°C. Mice bred without the gate couldn't tell the difference at all.

You already know this effect, even if you've never heard of TRPM5. It's why ice cream tastes only faintly sweet straight from the freezer and far sweeter once it melts in your mouth. Or why a flat, warm soft drink tastes alarmingly sugary.

So as your coffee cools towards the temperature of your mouth, your sweet-sensing cells hit their stride. The brown sugar and honey notes that were hiding at first come through, round and syrupy, like caramel loosening in a warm pan. Bitter signals are less affected by temperature than sweet ones, so as the cup cools, sweetness gains more ground than bitterness does.

In people the effect is real but more modest than in the lab, and probably not the only thing at work. Human taste is gloriously complicated: around half of us can taste something just from warming or cooling a bare tongue, a curiosity called 'thermal taste'.

Your nose does most of the tasting

Your tongue can only pick up a handful of basic tastes: sweet, sour, salty, bitter and savoury. Everything else you'd call 'flavour' (the blackcurrant, the cocoa, the toasted almond) is actually smell. When you sip, aromas drift up from the back of your mouth into your nose, a route scientists call retronasal smell. Pinch your nose while you sip and most of the coffee's personality simply vanishes. (Do try this at home. Perhaps not in a café.)

And aromas are very sensitive to heat. In 2017, researchers at the University of Copenhagen served one coffee at six temperatures, from 31°C up to 62°C, measuring the aromas it gave off while a trained panel tasted each cup. The hotter the coffee, the more aroma escaped, with a sharp rise above about 40°C. The big jump at 50°C and over came from roasty, toasty compounds, the ones that smell like the inside of a roaster.

The tasters noticed the difference too. The hottest cups came across as stronger, more roasted and more bitter. Between 31°C and 44°C, the same coffee was described as sweeter and brighter, with a note of tobacco appearing.

So a very hot cup is a bit like a dinner party where the loudest guest is the roast. As it cools, the roast lowers its voice, and the fruit and sweetness that were there all along finally get a word in. One useful consequence: the best time to smell your coffee is while it's hot, and the best time to taste it is a little later.

A cup in three acts

Put it all together and a single cup tells its story in stages. The temperatures are rough guides; every coffee, cup and kitchen is a little different.

Act	Roughly	What's going on	What you might notice
Just poured	60°C and above	The heat alarm is firing and roasty aromas are pouring out	Heat, roast, a firm bitterness. The best moment for a good sniff
Settling in	45 to 55°C	The alarm eases off and the roast aromas start to soften	A rounder, silkier cup, with sweetness starting to arrive
Warm	below 45°C	Sweet-sensing cells are near their comfort zone and the roast has stepped back	Sweetness, fruit and brightness at their clearest

Why coffee roasters taste everything more than once

It's why people who taste coffee for a living never judge a cup on one sip. At a cupping table, roasters and green coffee buyers taste each coffee hot, then warm, then cooler still, slurping noisily from spoons in a way that would get you gently asked to leave most restaurants.

Each stage tells them something different. A good coffee stays sweet and balanced all the way down. A less good one tends to get found out somewhere around the halfway mark, when the heat stops covering for it. Temperature, it turns out, is a very honest critic.

A few small things that change the cup

Milk. It rounds off acidity and adds its own natural sweetness, so a milky coffee changes more gently as it cools. Lovely, just a slightly different conversation.
The cup itself. A thick ceramic mug hangs on to its heat. A thin glass lets it go about as quickly as a Melbourne spring changes its mind. Warming the cup first slows the whole thing down.
How it's brewed. A small, intense espresso cools in minutes. A big pour-over or plunger gives you a much longer, slower stretch to taste your way through.
Patience. Hardest of all, and entirely free.

Try it at home

Next time you have ten minutes and nowhere to be, try this:

Brew a cup black, if you're game. Milk works too; the changes are just softer.
Take a sip straight away and notice what you taste. Don't overthink it.
Sip again at five minutes. Is it sweeter? Is there fruit you didn't find before?
Once more at ten minutes. Note what stayed, what faded and what arrived late.

You may well meet a flavour you've been drinking for years without ever being formally introduced. You may also find that ten minutes is a long time to sit still with a coffee. We'd gently suggest that's the other point of the exercise.

From all of us at Jasper Coffee, Melbourne coffee roasters since 1989. If all this has you curious, have a look at what's fresh from our roastery this week [link to coffees page].