Why does the coffee have to be roasted? The coffee roasting process. The aroma produced by roasting coffee.

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Coffee raw beans are warehouses full of chemicals.

Nutritionist Jonny Bowden lists coffee as one of the 150 healthiest ingredients on the planet and the number one source of antioxidant food in the American diet. Of all the ingredients and drinks, coffee is the most artistic, skillful and changeable, but it is also controversial. The complex composition of coffee, the complicated production process, and the chemical changes produced during processing are all important basic knowledge carefully studied by coffee researchers and enthusiasts.

Coffee raw bean is a warehouse full of chemicals, such as a certain type of Arabica coffee, which has identified more than thousands of ingredients, of which hundreds are aromatic and are the most fragrant in human drinks.

There are only 150 vanilla fragrances commonly used for seasoning in the catering industry, and even wine and tea are far less mellow than coffee. Coffee contains many high-quality acids, such as chlorogenic acid, citric acid, malic acid, acetic acid, phosphoric acid and quinic acid, as well as other organic acids, which are produced with the decomposition of carbohydrates during baking. at present, more than 30 kinds of organic acids have been determined, of which 15 are volatile. Generally speaking, the concentration of organic acid is the highest in moderate baking and decreases with heavy baking.

Carbohydrate

The carbohydrates in coffee beans can be divided into polysaccharides and low molecular weight carbohydrates, which include monosaccharides, disaccharides and trisaccharides, reducing sugars and non-reducing sugars, as well as some carbohydrate derivatives, such as gum. The contribution of carbohydrates to coffee lies in the change of aroma and color. In terms of aroma, carbohydrates will not only emit aroma after roasting, but also absorb other volatile aromas, making the coffee show a different special flavor.

The carbohydrate content of raw coffee beans is about 38.5%, of which about 8.7% belongs to low molecular weight carbohydrates, which will produce caramelization during the baking process and convert into ingredients such as caramel pigments, while polysaccharides and pectin are mainly cellulose (23.1%) or lignin (6.7%) components.

Low molecular weight carbohydrate

Sucrose is the main free carbohydrate in raw coffee beans, and its content varies with different varieties, sources and maturity. Other simple carbohydrates, such as reducing sugar, can also be detected from the extract of raw coffee beans, as well as glucose and fructose.

After roasting, the low molecular carbohydrates of coffee beans change, and the changes vary according to the degree of roasting. Sucrose is lost most rapidly, with a loss rate of 97% for light roasting, 99% for moderate roasting and 100% for heavy roasting. Glucose, fructose and arabinose are also lost to a considerable extent.

Polysaccharides

This is a very important ingredient of raw coffee beans, accounting for about 40-50% of the dry matter. By species, polysaccharides include polygalactose, polymannose, polyarabinose and cellulose, all of which make up the plastids of coffee beans.

Even after baking, polysaccharides will still preserve a certain amount. Previous studies have found that the effect of baking degree is not significant, and the retention rate is about 7075%. The retention rate of cellulose is the highest and that of polyarabinose is the lowest.

Protein and amino acids

The protein content of raw coffee beans is about 14.4%. After deducting nitrogen compounds such as caffeine and trigonelline, the protein content is about 11.9%. In addition to crude protein, raw coffee beans also contain a variety of enzymes, such as lipolysase (lipase), proteolytic enzyme, carbohydrate hydrolase, galactose hydrolase, peroxidase and so on. The coffee raw bean contains about 0.15-0.25% free amino acid, which has a great influence on the coffee flavor, but has a lower effect on the taste. Once the raw bean is roasted, its protein content will be reduced to 3.0%.

Lipids

Coffee oil (coffee oil) in the endosperm of raw beans and the wax in the outer layer of coffee beans together form the lipids of raw coffee beans. Coffee oil contains triglycerides and a considerable amount of other lipids, but its content and composition vary from variety to breed. Generally speaking, the average content of raw beans is about 11.5%. Even if baked, about 97% are still preserved in the form of lipids.

Volatile substances

Volatile compounds are the main source of coffee flavor, which greatly affects the quality of coffee. There are many kinds of volatile substances, and their existence will affect the aroma and quality of coffee, especially when roasting raw beans, especially when the volatile substances are cut off or derived from the reaction. All thermal decomposition or interactions between components, such as carbohydrates, amino acids, organic acids and phenolic compounds, will form the unique aroma and flavor of coffee.

In addition, the factors affecting the volatile components of coffee include the variety of beans, climate, soil conditions, storage of raw beans, baking temperature and time, and baking equipment.

Raw coffee beans must be roasted in order to produce the coffee aroma we usually smell. There is no special aroma of coffee before roasting. At present, it has been determined that the volatile aroma in raw beans can produce at least 650 kinds of aroma after baking, such as hazel, cream, caramel, grass, tobacco, scorch, spice and bitterness, etc. it is the largest variety of volatile aroma components in all food and beverages. in addition, the degree of roasting will also affect the flavor of coffee.

Moisture content

With different processing stages and products, the water content of coffee beans varies greatly. The moisture content of wet coffee beans with film is about 50%, that of dried raw coffee beans is about 11.5%, and that of roasted coffee beans is only about 4.8%. Because raw coffee beans contain a considerable amount of water colloidal macromolecules, such as proteins and polysaccharides, they can combine water in many different physical and chemical ways and exist in beans.