The Science Behind Coffee: What it Takes to Brew the Perfect Cup
Have you ever wondered what’s in your coffee? What gives coffee that complex flavour profile and mouthfeel? Or how your favourite illy blend always manages to taste the same? The secret may well lie in the chemistry of coffee.
Coffee Chemistry 101
So, what's in your cup?
Coffee contains volatile compounds – substances that give coffee its aroma – as well as non-volatile compounds which affect the perceived flavour of the drink and its biological reaction. Green coffee contains approximately 300 volatile substances. During various processes between harvest and consumption, many of these substances go through transformations and chemical reactions that define the final brew.
Caffeine is a natural alkaloid with a very faint bitter taste. It is slightly soluble in cold water and completely so in hot water. The amount of caffeine in a cup of coffee can vary depending on the species of coffee, with Robusta containing much more caffeine than Arabica, and the method of preparation. Water temperature and coffee extraction time greatly influence caffeine content. In general, we can say that the longer the water takes to pass through the coffee panel, or merely come into contact with it, the more caffeine is extracted.
Like caffeine, trigonelline is an alkaloid found in coffee beans. Trigonelline starts to decompose at 160°C. With the roasting process typically reaching up to 200-230°C, a lot of the compound is lost or broken down, producing important aromatic compounds in the process.
The gentle acidity, balanced with a certain level of bitterness, that is often sought-after by coffee aficionados is a result of the presence of acids in green beans. Some main acids in coffee include citric, malic, chlorogenic, quinic and phosphoric acids. As green beans undergo a series of chemical reactions during the roasting process, some of these acids change in concentration, contributing to some wonderful flavours and defining the overall profile of the brew.
Triacylglycerol, sterols and tocopherols, among others, are three lipids that can be found in green beans. They contribute to the texture and mouthfeel of a brew. The crema that floats on top of an espresso and the shiny coat of coffee oil encasing roasted beans are the most noticeable visual indications of lipids in coffee.
From Bean to Cup: Making of a Perfect Cup of Coffee
From the moment coffee cherries are harvested, illy’s coffee beans go through many processes that change the physical and chemical structure and define the sensory attributes of the beverage.
Selection: The Choice of Quality
After harvest and initial processing to extract the green beans, selection is next. Green beans are screened by size, weight and colour to create uniform batches and identify defective beans at their countries of origin. The green beans are then shipped to illy’s warehouse in Trieste, where they go through another round of selection. Any impurities, dirt and other objects that accidentally got into the bags are removed using a vibrating screen, magnets and extractor fans. The green beans then pass through bichromatic sorters that separate defective beans from high-quality ones based on their colourimetric characteristics.
Blending: Key to Consistency
Green beans used to create illy’s signature blend are blended before roasting. It gives the final product a more complex and balanced taste and a wider range of aroma compared to its single-origin constituent part.
As with every agricultural enterprise, each coffee harvest is different from the last. Depending on the harvest location and other environmental factors during the growing and cultivation process, each batch of green coffee illy sources can vary in aromatic properties. Blending ensures consistency in the quality of the coffee, even when the varieties and the characteristics of the individual origins change. That is why the illy blend, which consists of 9 Arabica beans from more than 50 origins in over 20 countries, always tastes the same.
Roasting: Releasing the Aroma Profile
A number of chemical reactions like the Maillard reaction and caramelisation occur in the roasting process, changing the chemical structure of the beans and releasing the blend’s aroma profile. Time and temperature greatly influence the quantity of aroma being released and the balance between acidity and bitterness of the roasted coffee. At illy, roasting reaches up to a maximum temperature of 200-230°C and can take anywhere from 90 seconds to approximately 40 minutes. Insufficient time stops short of completely transforming the chemical precursors and produces a bitter, metallic taste. Excessive time destroys the aromas that have already formed, reduces desirable aromas and brings out more bitterness. Since heating excessively compromises the finished product’s aroma, there is a rapid transition to cooling the beans once roasting is finished.
Pressurization & Ageing: Achieving Full Aromatic Complexity
Roasted coffee must be packaged as quickly as possible since exposing the beans to air leads to the oxidation of lipids (causing unpleasant aromas) and rapid dispersal of the aroma. Using the pressurisation system, patented by Francesco Illy, air (and thereby oxygen) is removed from the packaging. Nitrogen, an inert gas that doesn’t undergo chemical reactions with other elements, is then added to the packaging at a higher pressure than the atmospheric pressure to slow down the release of aromas in fats. This method allows aromas and freshness to not only be preserved but refined and elevated over time, undergoing a form of ageing process similar to wine. This is how the illy blend achieves its full aromatic complexity.
Preparation: Extracting the Essence of Coffee
After undergoing a series of transformations, the coffee beans are finally ready to be converted into a beverage — the coffee brewing itself. This is when water, grinding and extraction time come into play.
As an ever-present ingredient in any coffee-based beverage, water holds a vital role in the quality of the drink. The two important factors here are water hardness and its chlorine content. Water hardness is defined by the amount of certain dissolved minerals in the water. The amount and proportion of minerals and chlorine present in the water have significant effects on the flavour of your brew. For instance, having a certain level of calcium and magnesium can help extract flavours. Water temperature also plays a crucial role in brewing the perfect cup of coffee. The ideal water temperature varies by preparation but mostly lies in the range of 92-96℃, depending on the degree of roasting.
In coffee brewing methods that rely on percolation, such as espresso, water pressure and grind’s coarseness come to the fore. With this method, water passes through the coffee by either gravity, like that of Moka pots or pressure, for example, filter coffee. Even among pressure-based coffee brewing methods, the pressure required varies. Moka pots require substantially lower pressure than espresso machines. Since the pressure utilised is different, a suitable grind must be used. Ground coffee must be able to resist the flow of water adequately to ensure that the water can extract the aromatic substances upon contact.
Another critical variable in brewing coffee is the extraction time. A balanced extraction is packed with an array of flavours aromas with balanced acidity, sweetness and bitterness. Under-extracted coffee is when water is not given enough time to extract just the right amount of compounds. As compounds to balance off the acidity have not been extracted, the coffee may taste sour and salty and has a thin flavour profile. On the other hand, over-extraction also disrupts the balance of flavours as it over-extracts the bitter compounds in the coffee.
The optimal extraction time for each coffee brewing method varies. Espresso takes 30 seconds, while cold brew can take more than 12 hours of infusion.
All these variables and coffee preparation methods produce notably different bodies.
When it comes to taste, the keyword for illy is consistency.
By understanding the chemistry of coffee and using scientific approaches, illy has developed and perfected our processes so coffee aficionados around the world can recreate the signature illy taste wherever they are, day after day.