"Coffee roaster companion" the chemical substances of raw beans the structure and changes of coffee beans

Chapter 2: Raw Bean Chemicals

Written by Scott Rao

Translator: Chinese

Green coffee beans are hard, green seeds, 50% of which are different types of carbohydrates, and the other 50% are composed of water, proteins, lipids, acids, and various biological bases. Coffee roasters don't need to know the many chemicals in green beans to make good coffee, but knowing them will help them judge the quality of coffee beans and greatly improve roasting techniques.

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Carbohydrate

chemical structure

The structure of green coffee beans is a three-dimensional cellulose compound, or a polysaccharide, with each proton containing about a million individual cells. Cellulose in the matrix of green coffee beans interconnects hundreds of chemicals, which are converted into fats and water-soluble substances through the roasting process, thus determining the different flavors in brewed coffee. The cellulose structure in green coffee beans contributes half of its weight, but it doesn't play a big role in the flavor of roasted coffee, but it does capture volatile compounds that affect coffee aroma and add viscosity to brewed coffee, which is to increase the body we perceive through touch.

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Cellulose cellulose

Polysaccharide polysaccharide

Soluble Material Soluble substance

Volatile Compound Volatile compound

Viscosity viscosity

Body mellow

sugar

Sugar, mainly sucrose, accounts for 6% to 9% of the net weight of a coffee green bean, providing sweetness for our cup of coffee. Sucrose contributes to the development of fruit acids during coffee roasting, because during roasting, there is a reaction called the caramel reaction, in which sucrose produces a substance called acetic acid.

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Sucrose

Sweetness

Acidity

Caramelization

Acetic Acid Acetic acid

esters

Esters, mainly triglycerides, account for 16% of the net weight of a green coffee bean. Although esters are not soluble in water, they are present in coffee solutions extracted, especially in cups, espresso, French press, flannel, and other hand-brewed coffees. Esters help the extracted coffee retain its aromas (dry and wet) and add flavor. The ester content in coffee beans is directly related to the quality of coffee beans. The higher the content, the better the quality of coffee beans. Unfortunately, its presence in green coffee beans also affects coffee quality relatively, as it makes roasted coffee beans susceptible to oxidation and rancidity during storage.

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Lipids esters

Triglycerides

Mouthfeel

oxidation reaction

Rancidity reaction

Storage Storage

protein

Protein and free amino acids account for 10% to 13% of the net weight of green coffee beans. Amino acids and reducing sugars in coffee beans are pyrolyzed during roasting and polymerized in a series of non-enzymatic browning reactions often referred to in China as Maillard reactions. The Maillard reaction produces glycosamines and melanoids, which give coffee its bitter, sweet, brown, roasted, and roasted aromas.

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Protein Protein

Free Amino acids Free Amino acids

Reducing Sugars

Nonenzymatic Browning Reactions

Maillard Reactions Maillard reactions are called Maillard reactions in Taiwan.

Glycosamines Glycosamines

Melanoidins

Bittersweet sweet

Alkaloids: caffeine & trigonelline

Coffee contains two major alkaloids, caffeine and trigonelline, which each make up 1% of the net weight of a green bean and are one of the sources of bitterness in a cup of coffee and a major source of mild irritants. Caffeine accounts for 10% of coffee bitterness and plays a stimulating role in the body. Coffee trees produce caffeine to fight pests. The higher the elevation at which a coffee tree is grown, the lower the caffeine content of its coffee berries, because higher elevations have a lower risk of pests.

Trigonelline is perhaps the biggest contributor to the bitterness of the coffee we drink! However, it contains many directional compounds. During baking, trigonelline degrades to pyridine and nicotinic acid at high temperatures. Nicotinic acid is also known as niacin, or vitamin B3. Niacin causes a counter-cavity effect in 200 grams of coffee solution containing 20 to 80 milliliters (depending on the degree of roasting).

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Alkaloid alkaloids

Caffeine

Trigonelline trigonelline

Stimulating Property

Insect

Aromatic Compound Aromatic Compound

Degradation

Pyridine

Nicotinic Acid Nicotinic Acid

Niacin

Vitamin B3 Vitamin B3

Anti-Cavity Effect

moisture content

Ideally, the moisture content of the processed green coffee beans should be 10.5% to 11.5% of the net weight. If the moisture content is too low, the color of the green beans will fade, and the brewed coffee will have straw and hay flavors. To be a good roaster, you must be extremely careful about the fire control of low-moisture green coffee beans, which heat up quickly. If the moisture content of the coffee beans is higher than 12%, the coffee beans will grow hair and the brewed coffee will have a grassy smell. The moisture in green coffee beans slows heat transfer during roasting, so heat needs to be increased to evaporate. When roasting high-moisture green coffee beans, not only do you need more calories, but you also need to adjust the roasting time and heat.

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Fade

Moisture content Moisture content

Hay hay

Straw

Grassy, grassy

Heat Transfer

Evaporate

organic acid

Organic acids, mainly chlorogenic acids (CGAs) account for 7%~10% of the net weight of raw beans. Chlorogenic acid makes a cup of coffee sour, fruit acid, astringent and bitter. The high chlorogenic acid content of Robusta coffee beans makes it more bitter than Arabica coffee. Chlorogenic acid not only has antioxidant properties for coffee, but also has antioxidant benefits for the human body. There are also other organic acids in coffee, such as quinic acid, citric acid, malic acid, acetic acid, tannic acid, and formic acid.

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Organic Organic

Chlorogenic Acid Chlorogenic Acid

Astringency convergence

Antioxidant

Citric acid

Quinic

Caffeic tannins

Malic acid

Acetic acid

Formic acid

Gases & Aromatics

Volatile aromatic compounds provide aroma to our coffee. Green coffee beans contain more than 200 volatile substances, but they provide almost no aroma. Roasting coffee creates a large number of aromatic compounds, and so far scientists have extracted more than 800 volatile aroma factors from roasted coffee beans.

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Gas

Aromatics Aromatics

Volatile volatile