Have you ever been enjoying a hot cup of coffee, but noticed that once it starts to cool, the flavours and aromas seem to change? 

When this happens, you’ll probably start to pick up on nuanced and delicate flavour notes and aromas that you wouldn’t have been able to detect beforehand. You may find that your coffee now has a pronounced sweetness, fruitiness, or floral taste to it.

This change in flavour takes place thanks to specific chemical reactions that are triggered by fluctuations in temperature. To understand why and how they occur, you need to understand the science behind it.

Lee este artículo en español Cómo la Temperatura Afecta tu Experiencia al Tomar Café

Each cup of coffee contains dozens of aroma compounds that make up its unique smell and taste. Credit: Neil Soque

How Do We Perceive Flavour And Aromas?

Coffee is an incredibly complex drink. It has over 1000 aroma compounds that contribute to what we smell and taste whilst brewing and consuming it. Of these 1000 compounds, 40 significantly contribute to the aroma of coffee. 

Most of these aroma compounds are created during the roasting process, when the increase in temperature causes reactions with the sugars, carbohydrates, and nitrogen compounds in the green beans. As James Hoffman states in his book, The World Atlas of Coffee, the sugars break down due to the heat of the roasting process. At this point, they’ll either caramelise (resulting in those familiar caramel notes) or brown through the Maillard reaction. 

This process creates volatile compounds, which turn into gases that evaporate at room temperature. In this form, our ability to sense them is enhanced. We perceive these flavours and aromas through our tongues and noses as a variety of aromatic compounds associated with sweetness; ranging from chocolate notes to fruit notes.

The taste receptors for acidity, bitterness, and sweetness are found on the surface of the cells on our tongues. They react to the presence of certain chemicals and then forward this flavour perception to our brains. The chemicals in volatile compounds travel from our mouths to our noses to stimulate the olfactory system; a collection of organs in the nasal cavity. This process is also crucial in determining flavour and aroma.

When it comes to other flavours we perceive, various organic acids, sugars, oils, and caffeine contribute to what we taste. As Hoffman explains in the World Atlas of Coffee, the chlorogenic acids found in green beans can create a bitter taste, with quinic acid creating a bitter and astringent taste.

I spoke with Verônica Belchior, a certified Q-grader and coffee researcher, about what this means. She explained to me that this perception can be learned through association.

“If we have an acid aroma in our coffee, it can increase our perception of the acidity. This is because we learn [about] those volatile [compounds] in association with [their] basic tastes…we’ve always been exposed to a lemon aroma together with [an] acid taste. Once we have those together, the perception increases.” 

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You can’t enjoy a cup of coffee without relying on both your sense of smell and taste. Credit: Fernado Pocasangre

How Does Temperature Affect Extraction?

We all know that extraction can have a big effect on what flavours and aromas we perceive when drinking coffee. Here, the temperature of the brewing water can also have a significant impact on the coffee’s extraction rate.

“Each molecule has an optimum [amount] of extraction [it’s capable of] according to the water temperature. The hot water can extract most of the compounds we perceive in coffee, and…[the] hotter the water [is], [the] more extractable the compounds get.” Verônica explains.

When there’s an increase in the temperature of the water, the water’s molecules begin to gain more energy from the heat. They start moving faster, increasing the interaction between the water molecules and coffee molecules. 

The more these two molecules interact, the more extraction occurs. When this happens, the water molecules dissolve more compounds from the coffee molecules, affecting what we taste and smell in the drink.

“If we use low temperature water…we won’t extract [the] volatile [compounds] that are interesting for the full perception of coffee” Verônica states.

However, research indicates that this changes when it comes to drinks such as cold brew, that are extracted at low temperatures (ranging from 22°C to 5°C) for hours at a time.

Verônica tells me that “this leads [to] a complex sensory profile, since [the] balance of extraction of most of the compounds is achieved. [There] is a maximum…extraction of sugars, organic acids, chlorogenic acids, caffeine, [and other] less soluble compounds that need [more] time [to extract]”.

This long, low temperature extraction allows the sugars to fully extract, resulting in a mostly sweet, caramelised tasting beverage. Levels of bitterness and astringency also tend to be lower in cold brewed coffee.

Using heated water to brew coffee can dramatically impact both extraction and flavour. Credit: Neil Soque

Flavours And Aromas at Higher Temperatures

According to the National Coffee Association, the ideal serving temperature for coffee is between 82°C and 85°C. However, this would scald your tongue as temperatures in this range can exceed your thermal pain threshold. The most approved method of consuming coffee this way is through small sips or cupping ‘slurps’. This is where you only take in a small amount of liquid along with an inhale of air to cool the liquid down quickly.

Around 76°C is where flavour and aroma perception starts to take place. At this temperature, coffee releases a lot of vapour which enhances your perception of aromas, but can inhibit flavour perception. The volatile compounds are released faster and evaporate quicker here as well.

Higher aroma levels are perceived at temperatures around 70°C and can be maintained down to 60.4°C. These aromas tend to be described as ‘roasted’, ‘earthy’, and ‘intense’. Flavour tends to be trickier to perceive here, especially with more delicate notes of the coffee. In fact, research has suggested that various coffees roasted at a similar level are more likely to taste the same at higher temperatures.

The flavours that we perceive at 70°C are mainly bitterness, and as with the aromas, flavours associated with intensity and roastiness. 

These notes can linger until the coffee has cooled another 10°C, upon which we may detect an increase in bitterness. Bitterness has been found to be most intense at around 56°C.

As brewed coffee cools down, its aromas become harder to detect. Credit: Neil Soque

Flavours And Aromas Whilst Cooling Down

At temperatures below 50°C, you’ll see a significant change in the flavours and aromas of coffee. Aromas become harder to detect; mainly due to the reduction in vapour being produced as the coffee cools.

Bitterness starts to decrease, allowing for more intricate flavour notes to come through. It’s between 31-50°C that the highest number of flavours can be detected. These will mainly be those associated with acidity and sweetness. Around 44°C is when sweetness is at its most prominent. Bitterness is least detectable around 42°C. 

Between 31-37°C is when the smallest changes with the most interesting impacts can occur. Volatile compounds associated with sweet, fruity, floral, herbal, acidic, and nutty tasting notes are more prominent within this temperature range. It’s here where we really get to experience the defining characteristics of a coffee.

Acidity can be perceived best at lower temperatures such as 25°C, compared to at 44°C or 70°C. For example, drinking a cup of Kenyan coffee at this temperature will allow it to become more vibrant, with higher acidity levels. It allows us to taste the full range of flavours that a single origin coffee has to offer and shows us that the same coffee can taste different at different temperatures. The same cup of coffee would be less flavourful at a higher temperature.

Different blends of coffee will be more or less flavourful, depending on what temperature they are. Credit: Fernado Pocasangre

Whether you prefer your coffee scorching hot or as a cold brew, it’s important to understand the impact that temperature has on what flavours and aromas you perceive in it.

The next time you brew yourself a cup, make a note of what flavours and aromas you can perceive at different temperature ranges. Try to identify the ‘ideal ranges’ for bitterness, acidity and sweetness. 

it could help you determine what kinds of origins you should explore (ones with more pronounced acidity or sweetness), or which of these characteristics you prefer over others.

However you choose to do it, you’re bound to end up with a heightened appreciation of your favourite cup of coffee, at any temperature!

Enjoyed this? Then read What Temperature Should Your Cappuccino Milk Be?

Featured photo: Neil Soque

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