#Coffee Monday – nothing short of magic – roasting chemistry

From green to black. Picky like your teenage daughter. That’s the way it is. Today something about roasting chemistry.

Mysterious changes in composition. 
Have you ever wondered what does it take to make coffee so original taste? I recommend you to focus on acidity, aroma development, carmelisation and Maillard Reactions. Time of roasting is also important. Proper brewing extracts approximately 19-22% of roasted bean mass. The most significant change lays in water loss. What is interesting, despite what almost everyone has heard, DARKER ROASTING DOES NOT INCREASES CAFFEINE CONTENT. The amount of caffeine doesn’t change, as it’s stable at typical roasting temperatures, but proportion of weight increases during roasting. All because moisture changes. In lighter roasts a bean contains higher percentage of water. The other changes are presented on a chart below:

Magical changes during roasting
A little more than one-third of roasted coffee weight is water soluble. Proper brewing extracts approximately 19-22% of roasted mass (50-60% of soluble material). What is it in there?

Although many people can say that acidity is awful and makes coffee bitter or unpleasant (what that always try to mask by adding pounds of sugar) without acid coffee is flat and boring. If you want to try very low-acid coffee try brewing it with cold water for several hours. That kind of coffee is smooth and seems chocolaty a little bit, but as far as my opinion is concerned – pretty boring. The pH value of green bean is approximately 5,8- and roasted – 4,8. Most of all we can specify organic acid such as: CGA(more below), citric, quinic, caffeic, malic, acetic and formic. Malic acids contributes to a sour acidity and notes of apple. Phosphoric (an inorganic acid) on the contrary, found in concentration in KENYAN COFFEE IS RESPONSIBLE FOR ITS PRIZED AND UNIQUE ACIDITY. But acids concentration in beans decreased during roasting. That loss of their amount always makes dark roast less acidic that light one. Another important issue, what indicates to final acidity is elevation where coffee plant rise on (but it is another wide topic and there will be another article for that). Important is also that raw coffee’s sucurose content has a strong impact on its acidity potential and

What significant influences coffee’s body is CHLOROGENIC ACID (CGA). Is the mors prevalet acid in raw coffee beans. Robusta contains it more that arabica. Coffee is also a plant with the highest CGA content detected in any plant. CGA decomposes to quinic acid and caffeic acid – this two compounds contribute to the coffee’s body the most. In small percentage content are beneficial – makes brew bright and bitter, but more will produce undesirable levers of sourness ans astringency. That’s why it is important to pick coffee fruits before they get too ripe.

Reactions named below, and also degradation of amino-acids, sugars and phenolic acids release in coffee so unique bunch of scents. Caramelization process adds to brew notes of fruity, caramelly, nutty and similar aromas. Maillard reactions – additional – produce savory, floral, chocolaty earthy and roasted aromas. Remember only, that LIGHTER ROASTING PRODUCE MORE AROMATIC COFFEE. It happens due tothat beans gradually lose aroma during storage. Darker roast with weaker and more porous cellulose structrure, lose aromas more quickl that ligher do.


Maillard reactions are nonenzymatic browing reactions between fee amino acida and reducing sugars. They occus during cooking of many foods – as to my mind – example which presents the closest view on it – it’s browning of meats. Think about effects of boiling and roasting method of flavour of meat. Spot the complexity, depth and wide range of aromas – absent in boiled ones. Although most people associate the wor caramel with something sweet, mockingly, it decreases sweetness and increases the bitternes. So – it means that ligher roasts are sweeter and darker – bitter, because of caramelization.

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