Updated: Sep 1
Have you ever enjoyed a cup of hot coffee and noticed that, as the temperature starts to decrease, the flavors and aromas seem to undergo a transformation?
The changes in these flavors occur due to specific chemical reactions that are activated by the temperature shift. To understand why and how they occur, let's explore the scientific properties behind the impact of heat with iO Coffee in today's blog!
How do we perceive smell and taste?
Coffee is an exquisite and complex beverage. Within it, there are over 1000 aroma compounds contributing to what we perceive while brewing and savoring. Among them, around 40 compounds truly influence the aroma of coffee.
These aroma compounds are primarily formed during the coffee roasting process, as the temperature increases, causing reactions with sugars, carbohydrates, and nitrogen compounds within the green coffee beans. According to James Hoffman in his book, "The World Atlas of Coffee," sugars break down due to the heat during roasting. At this stage, they can either create caramel candy-like flavors (leading to familiar caramel notes) or transform into a brown color through the Maillard reaction.
This process generates volatile compounds, transitioning into gaseous form at room temperature. In this state, our ability to perceive them becomes heightened. We perceive these flavors and aromas through our tongue and nose as a range of fragrant compounds linked with sweetness; from chocolate notes to fruity undertones.
The tastes of sourness, bitterness, and sweetness reside on the surface of cells on our tongues. They react with the presence of specific chemical compounds and then transmit the sensation of these tastes to our brains. Volatile compounds move from the mouth to our nose to stimulate the olfactory system; a set of organs located in the nasal cavity. This process is also crucial in determining flavors and aromas.
When discussing other flavors we perceive, organic acids, sugars, oils, and caffeine contribute to what we experience when savoring. As Hoffman explains in his book "The World Atlas of Coffee," chlorogenic acids in green coffee beans can create bitterness, and quinic acid can generate an unpleasant bitter and sour taste.
Verônica Belchior, a coffee expert, explains that this perception can be learned through association. "If we perceive the acidic aroma in coffee, it can enhance our perception of acidity. This is because we learn about those volatile compounds through their combination with basic tastes... we are always exposed to citrusy aromas along with the acidic taste. When we have both together, the perception increases."
The impact of temperature on the coffee extraction process
We often know that the extraction process greatly influences the flavors and aromas when enjoying coffee. However, the temperature of the water used for brewing coffee also plays a crucial role in this.
"For each molecule, there's an optimal temperature for the best extraction. Hot water can extract more compounds from coffee, and as the water gets hotter, the compounds are easier to extract," explains Verônica.
Increasing the temperature makes the molecules in the water more energetic. They move faster, resulting in more interactions between the water and coffee. This interaction leads to greater extraction. The water dissolves more compounds from the coffee, impacting the flavor and aroma of the cup of coffee.
"However, if cold water is used, we don't extract the intriguing volatile compounds of coffee," Veronica says. But this changes for cold-extracted coffee like cold brew, which is extracted at low temperatures (from 22°C to 5°C) over several hours. This extended low-temperature extraction process allows sugars to fully dissolve, creating a beverage with a sweet and creamy flavor, along with caramel notes. The levels of bitterness and astringency are typically low with this cold extraction method.
Flavor and aroma at high temperatures
According to the World Coffee Association, the ideal temperature for enjoying coffee ranges from 82°C to 85°C. However, this temperature range has the potential to burn your tongue, as it surpasses the threshold of heat pain your body can endure. A refined way to savor coffee at this temperature is to take small sips or perform gentle "slurps." This implies taking a small amount of coffee into your mouth, accompanied by a light breath to cool it quickly.
Around 76°C, the perception of flavor and aroma starts to become distinct. At this point, coffee releases more steam, creating conditions for perceiving rich aromas, but simultaneously limiting the full presence of flavor. Volatile compounds increase rapidly and evaporate quickly in this environment.
Higher levels of aroma are often sensed at temperatures around 70°C and can persist down to 60.4°C. These aromas are often described as ' 'earthy,' and 'bold.' Flavors are usually harder to perceive here, particularly the delicate notes of coffee.
The flavors we perceive at 70°C are predominantly bitter, and similarly, with aromas, they relate to strength and roast character. These notes might still linger until the coffee cools by about 10°C, after which we can sense an increase in bitterness. It has been found that bitterness is at its highest around 56°C.
Flavor and aroma change as the coffee cools
At temperatures below 50°C, you will notice a significant change in the flavor and aroma of coffee. Aromas become harder to perceive, mainly due to the decrease in steam as the coffee cools.
Bitterness starts to diminish, opening up opportunities for more delicate flavor notes. The key range for perceiving various flavors is from 31°C to 50°C. These primarily relate to acidity and sweetness. At around 44°C, sweetness is most pronounced, while bitterness is less noticeable at approximately 42°C.
From 31°C to 37°C is the window where subtle changes with the most intriguing effects can occur. Volatile compounds associated with sweet, fruity, floral, herbal, acidic, and nutty notes become more apparent in this temperature range. This is where we truly experience the defining characteristics of a cup of coffee.
Acidity is best perceived at lower temperatures like 25°C, compared to 44°C or 70°C. For example, drinking a cup of Kenyan coffee at this temperature will make it more vibrant, with a higher acidity level. This allows us to experience the full range of flavors that a single-origin coffee can offer and shows us that the same type of coffee can have different flavors at different temperatures. The same cup of coffee will have fewer flavors at higher temperatures.
Whether you enjoy piping hot coffee or chilled cold brew, understanding the impact of temperature on the flavors and aromas you experience is crucial.
Next time you brew yourself a cup of coffee, take note of the flavors and aromas you can perceive at different temperature ranges. Try to identify the "ideal" ranges for bitterness, acidity, and sweetness.
This can help you determine which coffee origins you should explore (ones with prominent acidity or sweetness), or which characteristics within these attributes you prefer over others. Discover the nuances of your favorite cup of coffee every day!