Coffee roasting is the action of cooking, heating, toasting to transform the green coffee bean into a roasted coffee bean. The material used for this cooking process is called a roaster.
Among the factors that make up the organoleptic characteristics of a coffee we find
- The origin and variety of coffee,
- post-harvest processing conditions,
- roasting parameters,
- the conditions of preparation of the coffee drink.
- dehydration and swelling of the coffee beans at high temperatures,
- the thermal decomposition of certain chemical compounds, in particular, aroma precursors
- the formation of aromatic constituents through the Maillard reactions.
We’ll take a look at:
- 1 Roasting coffee beans processes
- 2 Roasting coffee beans Guide
- 3 Chemical modifications of coffee beans
- 4 Grind coffee beans
- 5 Packaging and storage of coffee beans
- 6 Decaffeination
- 7 To obtain decaffeinated coffee, you can choose one of the three existing methods:
- 8 THE REACTIONS OF MAILLARD
Roasting coffee beans processes
They are carried out by:
- direct heating, the oldest process which is no longer used industrially,
- Indirect heating: the most commonly used process
- fluidization in a hot air stream: recent process.
These processes use different modes of heat transfer: conduction and convection.
Conduction: the heat transfer is carried out by contact between the walls of the roaster and the coffee beans. The roasting conditions, in this case, depend very much on the characteristics of the material used.
Convection: the heat transfer takes place directly between the hot air and the coffee beans. The speed of heat transfer depends on the conduction and absorption capacity of the coffee beans.
Roasting coffee beans Guide
See how to roast the coffee beans like a professional :
Chemical modifications of coffee beans
Apart from the decrease in H2O content, the start of roasting is due to important chemical changes, degradation, polymerization of certain compounds of coffee beans: proteins, sugars, acids, alkaloids, etc….
Proteins: the content in green coffee beans varies from 10% to 13%. They are rapidly denatured by heat (about 30M) and break down into amino acids. These are either degraded or they participate in the Maillard reactions with sugars to give certain aromatic compounds.
Sugars: simple sugars (4% to 8%) disappear completely either by degradation or by participating in the Maillard reactions. Polysaccharides (45% to 55%) are degraded during roasting to water-soluble substances. On the other hand, the contents of cellulose and hemicellulose (fibers) remain practically unchanged.
Acids: The acid content is very important because these compounds actively contribute to the development of aroma and taste. This content varies according to the variety and post-harvest treatments.
Volatile acids develop during roasting at temperatures between 160°C and 190°C. At high temperatures, their content decreases.
The non-volatile acids are degraded and the degradation is a function of the degree of roasting (from 15% to 50%).
Chlorogenic acids, whose contents are high in green coffee (7% to 14%), are partially degraded and their degradation products directly participate in the taste, in particular the astringency.
Caffeine and alkaloids: Approximately 10% of caffeine is lost during roasting by sublimation. This loss is all the more important as the roasting process is pushed forward.
Trigonelline is strongly degraded (70% to 100%) and its degradation products contribute to the development of the aroma.
Grind coffee beans
Just ten years ago, 60% of coffee was sold as beans and 40% was ground. The proportion of ground has increased considerably; the old grinders, stone, or hammer mills, which crushed the coffee giving a very irregular grain size have been advantageously replaced by fluted metal roller mills that cut the coffee and give it a perfect grain size. These cylinders are cooled by circulating recycled water and maintained at a constant temperature of 12 °.
This way, there is no risk of heating or spoilage of the product. The techniques have improved the quality of ground coffees as well as ease of packaging and use for coffees presented in pods or capsules.
NB: A bean coffee will be oxidized in 15, 20 days / a ground coffee in 5 days.
- Powdered or floury grind: it is suitable for the preparation of Turkish coffee.
- Fine or very fine grind: suitable for espresso-type coffee makers and coffee makers using a paper filter.
- Medium grind: grind to be used for vacuum and permanent filter coffee makers.
- Coarse grind: used for traditional, French press and Italian coffee makers.
1 How To Grind Coffee beans at home and Without A Grinder
2 Grind coffee beans: 7 Different Grinding Procedures
2.1 How to grind coffee beans with a blender
2.2 How to grind coffee beans with a Mortar and pestle
3 How to grind coffee beans with a Hammer
3.1 How to grind coffee beans with a Knife
4 Others methods to grind coffee beans at home
5 what size to grind coffee beans
5.1 Use a coarse bean for a plunger coffee maker
5.2 Prepare a medium grain for many methods
5.3 Finely grind the coffee for espresso
5.4 Use a very fine bean for Turkish coffee
Packaging and storage of coffee beans
Coffee should be consumed freshly roasted because after roasting the coffee :
- Releases carbon dioxide (CO2 neutral gas) under internal pressure and therefore loses its aroma.
- Oxidizes on contact with oxygen in the air.
- Lipids go rancid.
- Remains very sensitive to foreign odors.
Hence the need to keep it away from air and light, without this protection, coffee beans will be oxidized in 15 days, ground coffee in 5 days and brewed in 1 hour if heating is maintained.
There are three main packaging methods
- Hard vacuum (with prior degassing for 4 to 6 hours)
- The valve vacuum (which allows immediate packaging)
- the vacuum-packed metal box.
These methods can be used with packages of materials laminated with plastic and aluminum foil which guarantee an effective barrier against air and light or with aluminum metal cans. Coffee is sensitive to heat and humidity and must be protected from foreign odors that could alter its aroma.
Some people can’t stand caffeine or don’t want to consume it. Decaffeination is the removal of caffeine from coffee. It is an industrial process that takes place in green coffee. There are several extraction methods:
- By organic solvent
- By liquid CO2 and in the supercritical phase
- At the water
The goal of decaffeination is to obtain a coffee that retains all of its aroma and taste despite the processing required to extract the caffeine.
History of decaffeination
The first successful extraction of caffeine from green coffee beans was performed by the German chemist, Runge, in 1820.
However, the real technical development did not take place until the beginning of the 20th century, when Ludwig Roselius decided to subject green coffee beans to a pre-treatment with steam before bringing them into contact with solvents which extract the caffeine.
Remember that Robusta coffees generally contain between 1.6% and 2.6% caffeine while Arabica coffees contain much less, i.e. between 1.2% and 1.6%.
To obtain decaffeinated coffee, you can choose one of the three existing methods:
The traditional method of using organic solvents:
The green coffee is subjected to a jet of saturated steam to make it porous, then it is steeped for several hours in a solvent bath, then it is “washed” with plenty of steam. The details of the steps are as follows:
The beans are cleaned in large drums, then moistened with water vapor in the extractors to make them swell until the proportion of water naturally contained in the beans has increased to about 30%.
The caffeine is then removed by diffusion in the liquid phase in the extractors using organic solvents (methylene chloride or ethyl acetate) heated to temperatures between 40 ° and 70 °.
The caffeine is then extracted through the large pores on the surface of the beans and removed by the solvent.
Then, the coffee is steamed to remove all traces of solvent. It is then dried to regain its initial moisture content. After decaffeination
The supercritical CO2 process:
- A liquefied gas, generally CO2, or in the supercritical phase and under very high pressure is passed over the coffee.
- This gas then takes care of the caffeine.
- This gas is washed with water, which removes the caffeine, at the same time causing decompression.
- The decaffeinated beans are then dried.
The water-based process associated with activated carbon:
This process requires the use of a more delicate implementation. A very precise analysis of the batch to be treated is carried out. The constituents of coffee are thus determined.
There are two ways to do this:
- Extraction of the caffeine from the green coffee with water, in a counter-current system, followed by passing the extract over specially selected activated carbon to more preferentially adsorb the caffeine. The caffeine-free extract is then reincorporated into the corresponding green coffee, which is then dried.
- Using an isotonic aqueous solution of decaffeinated green coffee to extract caffeine from green coffee. The isotonic solution contains all the elements of an aqueous extract of green coffee except caffeine, and this in proportions specially adjusted to be in short saturated in these elements and then only solubilize caffeine during contact with a green coffee still containing caffeine.
When making soluble coffee, the quality of the blend is of prime importance. The manufacture of soluble coffee is based on the principle of desiccation of coffee obtained by infusion. The powder obtained (or soluble coffee) makes it possible to reconstitute the drink by simply dissolving it in water.
It is obtained from coffee filtered in large percolators and concentrated. This coffee concentrate sprayed in a stream of hot, dry air (atomization). The dried coffee particles thus obtained are received at the base of the atomizer (cylinder up to 15 meters high in which the liquid coffee is vaporized). The quality of the product thus obtained is coarse and irregular.
Another process, freeze-drying, makes it possible to transform the coffee into granules of better quality, by the principle of sublimation. This sublimation is only possible because it takes place under vacuum and the heating is regulated automatically, with the greatest precision. This is how those brown granules typical of freeze-dried coffee are formed.
We also start with a concentrated coffee that we freeze at –40 °. We place this frozen coffee in bars in a freeze-drying chamber where we create an absolute vacuum, the water boils at 0 °. In this way, when a vacuum is obtained, the water with which the coffee was made sublimates, that is, it goes directly from a solid-state to a gas state. The small granules of freeze-dried coffee then remain.
THE REACTIONS OF MAILLARD
At the beginning of the roasting, water and sugars will give caramels. Nothing else happens as long as the water remains, i.e. until the tenth minute. And only then, when all the moisture has disappeared (less than 1% remains), the four groups of acids, in reaction with the sugars, will develop the coffee’s aromas.
===+ To put the complexity of the operation in context, it should be noted that while orange juice contains three aromatic compounds, coffee contains a thousand!
The reading of the chromatogram established during a roasting perfectly illustrates this complexity: ten minutes of caramelization, with only four aromas, then the fireworks, the explosion of all the others. Some are born and last. Some will marry together to give birth to a new aroma. Others will disappear.
This is how, during the roasting process, the aromatic intensity appears at the tenth minute, increases sharply, and then decreases at the end of the operation. Each product has its own kinetics of formation and disappearance.
At each moment of the roasting process, there is a specific composition of the volatile fraction and therefore of the aroma. All this has been perfectly studied and codified. These are the reactions of Maillard, named after the chemist who analyzed them. The essential goal of roasting is to develop the aromas but many other reactions will occur such as the reduction of acidity, the increase of bitterness…