The roasting of coffee

Roasting: this heat treatment causes significant chemical and physical changes in the structure and composition of raw coffee, causing the beans to darken and emit the characteristic aroma of roasted coffee.

1. The purpose of coffee roasting

The main purposes of coffee roasting are: a, aroma; B, increase the complexity of coffee; C, get color; D, form the unique flavor of coffee and so on.

2. The way coffee is roasted

According to the baking time, it can be divided into two types: fast baking and slow baking. According to the baking machine, it is divided into two types: family workshop type and industrial type. We mainly know about industrial baking.

Project

fast

Slow speed

Baking machine

Hot gas stove, also known as flow bed (HOT AIR ROASTER)

The beans are baked by a vortex formed by a high-temperature air. due to the strong air flow, the coffee beans are constantly blown up and suspended in the furnace without the need for metal blades to stir.

Roller furnace, also known as roller type (DRUM ROASTER)

When the gas is heated through the bottom of the furnace, the coffee beans are gradually heated by the air, and the metal blades in the furnace keep stirring the beans.

time

As short as 90 seconds (traditional time is 12 minutes)

Up to 40 minutes (traditional 12 minutes)

Production scale

Large, high output, about 1500-4000 kg / h.

Small, low output, about 700 kg / h.

Advantages

The strong hot air conducts heat well, and the coffee beans are heated more evenly, and the desired baking degree can be achieved in the shortest time, thus reducing the disappearance of coffee oil and cell tissue damage, and the baking time is mostly within three to eleven minutes. Due to the short time, the weight loss of coffee beans is less, which can save money, so most of the people who use this processing method are large companies.

Just start baking at a warm heat, and then slowly increase the heat after an explosion, so as to prevent the water in the beans from evaporating too quickly and minimize the damage to the cell and tissue. Only by heating step by step can the flavor of coffee beans be fully displayed.

Areas with poor economic conditions usually use long-term baking because most consumers can only afford low-cost, defective coffee beans.

Shortcoming

Without sufficient reaction time, the residue of polyphenols leads to a metallic bitterness. At the same time, due to high-speed processing, volatile aroma molecules are not formed.

Baking for a long time can drive out the bad taste and smell. But the favorite smell and aroma are also gone.

Flavor

Sour taste is more obvious, more layered.

It suppresses the sour taste and the taste is low and sweet.

Chlorogenic acid

There are many residues.

Less residue

3. The roasting process of coffee

The first stage of baking is endothermic, in which raw coffee beans are slowly dried until they change to a yellowish color, and the baking smells like toast or popcorn.

The second stage, commonly known as the first crack, usually occurs at about 205C, during which the coffee beans double in size, change to a light brown color and lose about 5 per cent of their weight.

The third stage is the first explosion to the second explosion, the temperature rises from 205 degrees Celsius to about 220 degrees Celsius, the color changes from light coffee to moderate coffee, and the weight loss is about 13%. This chemical process is called pyrolysis, which converts the chemical composition of coffee beans and releases carbon dioxide. The third stage is the second endothermic period, followed by the second exothermic period (exothermic), called the second explosion (second crack). The second pyrolysis takes place at about 225-230 degrees Celsius, baking a medium-deep brown color, and the sound of the second explosion sounds dense and fast, and the surface of the coffee bean is covered with a layer of oil.

In the process of segmented heating in a bean dryer (usually using a large, hot rotating cylinder), the remaining water in the coffee bean cells turns into steam, prompting the rich carbohydrates, proteins, lipids and minerals to undergo a variety of complex chemical reactions. Coffee beans begin the caramelization process between 170C and 200C. At 185240C, carbohydrates combine with amino acids, peptides and proteins for caramelization, also known as the Mena reaction (maillard's reaction).

Caramelization is one of the most important factors affecting the flavor of coffee. After baking for 6-7 minutes, raw beans absorb a lot of heat and start the pyrolysis reaction.

Pyrolysis can last until the second explosion, although caramelization is an important process to awaken the aroma of coffee, but with the extension of baking time, some ingredients will also be carbonized to form a bad astringent bitter substance, how to get the highest caramelization. At the same time, carbonization should be reduced to the lowest point, which is the highest technical link of roasting coffee beans.

During the roasting process, the volume of coffee beans increases by at least half, while the weight of beans decreases by 1. 5%.