What makes coffee so aromatic and gives us the morning fix? This section highlights the chemical composition of the bean.
Arabica contains more lipids and trigonelline, while robusta contains more caffeine and chlorogenic acids.
Coffee bean is best stored to achieve humidity of between 10% to 12.5%, beyond where there may be risk of microbiological spoilage.
Coffee contains about 4% minerals of which potassium takes up 40% of its total.
Processed coffee bean contains about 50% carbohydrates as compared to green bean
Sugar content of coffee bean: arabica: 6-9% while robusta: 3-7%. Glucose content has been negatively correlated with aroma level and positively with cup sweetness, while fructose content has been negatively correlated with sweetness.
There are several types of acids in coffee beans: carboxylic acids, chlorogenic acids and amino acids.
Carboxylic acid content between arabica and robusta is about the same. Major carboxylic acids include quinic acid, malic acid, citric acid and phosphoric acid. Quinic acid content is affected by factors such as processing, fermentation and age. It can increase to 1.5% in old beans. These acids contribute to the acidity of the coffee. Quinic acid imparts a slightly sour and sharp quality, but it adds cleanness to the cup. Malic acid, though more acidic than citirc acid, is only 0.3-0.7% in green bean and can lose around 30% at medium roast. As an inorganic acid (due to absence of carbon in its structure), phosphoric acid contributes significantly to the acidity of coffee.
Chlorogenic acids are a group of phenolic acids esterified to quinic acids. They made up to 10% of the green bean weight.
Amino acids are present in raw bean at about 1%. But these are easily loss during green bean storage at elevated temperature due to enzymatic browning effect
Fatty acids are present as glycerol esters in triglycerides. Examples of fatty acids are the stearic acid and oleic acid where the proportion of stearic acid is less than the oleic acid in robusta, but about the same in arabica. The ratio of stearic to oleic acids may give an indication of robusta content in coffee blend
Raw bean contains trigonelline at 0.6-1.3% in arabica and 0.3-0.9% in robusta. It contributes to bitter taste in the brewed coffee.
Caffeine content in arabica is about 1.2-1.3%, while robusta contains about 2.2-2.4%.
There is about 10% proteins in green bean.
Coffee oil, or lipids, averages around 15% in arabica and less than 10% in robusta
