Roasting Chemistry – The roasting process is pure magic for coffee lovers: thick, dull-tasting coffee transforms into ambrosial brown beans with a non-toxic scent. Many reactions occur during the roasting process, including Maillard Rxns and caramelization, browning coffee beans, and creating new taste trams and flavor compounds.
The roasting procedure also makes the seeds brittle enough to ground readily and hollow sufficient for water to enter and extract flavors dissolved in the roots. Let’s learn about chemical composition when roasting coffee.
1. Changes in Chemical Composition
By weight, more than a third of roasted coffee is water-soluble. The glass should be extracted to roughly 19-22 percent of the mass of roasted coffee (or at about 55-60 percent in the water-soluble matter, plus small amounts of lipids and cellulose fragments, aka “fines”).
According to this perspective, the loss of water from the grain (humidity reduces from 12 percent to 2 percent of particle mass) and the rise of CO2 is the most critical changes in particle composition after roasting (from negligible long to 2 percent of the particle mass). Due to dryness, the related quantity of the driest component rises by up to 1%.
During roasting, their bulk does not vary considerably, but the proportion of the total mass of the seeds rises. Note that the values in the pie chart are estimated standards; the actual rate will vary based on the kind of coffee used, the roasting stage, and other variables (from R. Barter (2004). A quick overview of roasting profile theory and practice. Tea & Coffee Trade Journal, vol. 68, no. 34-37, republished in Tea & Coffee Trade Journal).
2. The development of acids during roasting
Acidity adds vitality, refinement, complexity, and brightness to coffee. Even though many coffee consumers believe the edge makes coffee bitter or unpleasant, coffee without acid is flat and dull. By extracting a cup of coffee with chilled water for a few hours, people may get a cup of coffee with minimal acid. Such coffee may taste silky and chocolaty, but it lacks nuance and becomes monotonous.
CGA is the most common acid in coffee fillings, accounting for 6-8 percent of dry weight, and coffee has the greatest CGA of any plant. The CGA adds significantly to the acidity and bitterness of brewed coffee and provides some mild stimulant effects.
The structure of the CGA is progressively disrupted by roasting. There’s around 50% remaining, while in dark roasts, there’s about 20% left in dark roasts. Quinic and caffeine acids, two bitter phenolic chemicals that contribute to the body of coffee, are formed when CGA is broken down. Quinic and caffeinated acids offer helpful brightness and acidity to foods in tiny doses, while significant amounts generate undesired sourness and astringency ( sourness and astringency).
In low quantities, other minor organic acids in coffee enhance the flavor, but they produce an unpleasant taste when imbalanced. The concentration of these acids typically increases and peaks at the light roast level, then steadily drops as the roasting time progresses. Black roasted coffee is less sour than lightly roasted coffee due to decreased organic acids during roasting.
Citric acids give coffee its acidity. Acetic acid contributes to the winey edge in small doses, but vinegary bitterness is generated in insignificant amounts. Clean, sour acidity and apple notes are provided by malic acid. Phosphoric acid, a high-concentration inorganic acid found in Kenyan coffee, might explain the country’s noteworthy edge. The potential amount of acidity is often determined by the height at which the coffee plant is cultivated. At the same time, the whole natural environment, particularly humidity, explains the kind of acid generated.
A lower pH result implies increased acidity, and vice versa, when testing the edge of coffee by pH. The bite of the coffee is most substantial during the first crack phase and gradually lowers as it roasts. The coffee’s pH multiplies to about 5.8, drops during roasting, and troughs (i.e., levels of acidity peaks) in 1st crack, around 4.8, before gradually climbing again as roasting progresses.
The organoleptic impression of acidity is determined by a mix of edges measured in coffee and a unique balance of acids. As a result, a coffee drinker’s true sense of sharpness is linearly proportional to, but not equal to, quantifiable acidity.
The amount of sucrose sugar in the coffee filler significantly impacts the possible acidity and sweetness following roasting. Because Caramelization creates acetic acid, sucrose adds to the edge. As a result, coffee farmers must harvest mature fruits since chin seeds contain more sugar. Light roasting decomposes roughly 87 percent of sucrose, whereas burned/blacker roasts disintegrate nearly 99 percent.
3. Aroma Development
The ideal smell production does not begin until after a few minutes of the roasting process. When the moisture content of the particles falls below 5%, volatile aromatic chemicals form quickly. Aromatics are produced through caramelization and Maillard reactions and the degradation of amino acids, sugars, phenolic acids, and lipids.
Fruit, caramel, and pea tastes are created by Caramelization, whereas savory flavors, flowers, chocolate, soil, and roasted/grilled flavors are produced by the Maillard reaction. Many of the volatile aromatic chemicals in coffee are dissolved by the oils in the beans, which gently release the scent during and after brewing. Mild to medium roasting produces the most odor.
When incense is burnt for extended periods, its destruction outpaces its formation, and the aromatics grow smokey and spicy. The outgassing process causes roasted seeds to lose their scent over time. Roasting produces a more combustible cellulose structure with a weaker and porous cellulose structure, absorbing aromatics faster than mild roasting.
4. Maillard Reactions and Caramelization
MRS in a browning reaction between free amino acids and reducing sugars that do not need the use of enzymes. These processes give coffee its color, sweet bitterness, and a lot of taste. MRS are formed during the cooking of several meals, but most typically during beef browning.
Consider the differences in the impacts of roasting/grilling and steaming up the flavor of the meat to appreciate the relevance of MRS to taste: Roasting/grilling meat produces a wide range of tastes, complexity, and depth of flavor that steamed/boiled meat lacks. For coffee beans, MRS has a similar function.
When the temperature within the seeds reaches a level high enough to boil all of the water in the sources, the temperature rises quicker, causing the Mrs to accelerate. That is why, at medium roasting, the scent proliferates. At temperatures over 160 degrees Celsius, MRS becomes self-sustaining.
Unlike the Mrs reaction, Caramelization takes the form of pyrolysis or thermolysis. Roasting heat breaks down sugar molecules and records hundreds of different compounds, including smaller, sweeter, flavorful molecules and those bigger than brown but tasteless, starting at 171 degrees Celsius.
Although most people associate “caramel” with a sweet dessert, the caramelization process, strangely, diminishes the sweetness of food and drinks while increasing the bitterness. Because of Caramelization, lighter roasting is sweeter, whereas deeper roasting is bitterer and caramelized.
5. Caffeine Content and Roasting
Darker roasting does not diminish the quantity of caffeine in coffee beans, contrary to popular belief. Roasting keeps caffeine levels almost constant since caffeine is stable at any roasting temperature. If you believe that when coffee beans are roasted, they lose mass, then the caffeine-to-weight ratio will rise.
As a result, a person extracting a cup of coffee at any roasting level with a specific proportion of water/amount of powdered coffee, rather than volume, roasted fire, will get coffee with a more significant caffeine percentage.