The secret of coffee's charming aroma

The taste of coffee is intoxicating, the aroma of coffee is addictive, even Napoleon could not resist the charm of coffee. There is such a story behind this.

According to legend, a few days before Napoleon died on St. Helena in 1821, his attendant Marshal Bertrand wrote about Napoleon’s desperate begging: “He has asked for coffee twenty times this morning and asked if I could give him a few more sips. ‘No, sir, the doctor ordered only one spoonful of coffee. It’s not time yet. Your stomach is not good. Drinking too early will only make you vomit too early.’ He has already vomited nine times this morning. He used to be a hero who led a powerful army and was feared by everyone. Now he has fallen to begging for coffee and is as obedient as a child. He begs again and again, and is rejected again and again, but he is not angry. This scene is heartbreaking.”

01The Secret of Aroma

Many coffee lovers can relate to this obsession with coffee. It is a blessing to wake up every morning and smell the aroma of coffee. Why is the aroma of coffee so intoxicating? The secret lies in the ingredients of coffee itself. It is rich in carbohydrates, proteins, organic acids, etc. These ingredients produce a series of reactions during the roasting process, and the aroma is produced.

Among them, the two most important reactions are caramelization (oxidation and browning of sugar) and Maillard reaction (reaction of amino acids and sugars). Both reactions require the participation of sugars, and the abundant sucrose in green beans just provides the materials needed for these two reactions. Previous studies have also found that sucrose content is positively correlated with the flavor of coffee beans. It is understood that the sucrose content of Arabica in green beans is twice that of Robusta, which also explains why the flavor of Arabica coffee beans is better than that of Robusta.

The secret of coffee aroma lies in caramelization reaction and Menard reaction. Let’s take a look at the details of these two reactions.

02Caramelization reaction​​

The sugar in coffee beans undergoes caramelization at about 170-200℃, which is exactly the melting point of sucrose (185℃) and the temperature of the first crack stage when roasting coffee beans. The products of the caramelization reaction are divided into two parts: the dehydration product of sugar, which is caramel or sauce color; and the cracking product, which is mainly some volatile aldehydes and ketones.

In general, the caramelization reaction produces roasted aroma, caramel and color, as well as other aromatic substances such as maltol, cyclotene, furan compounds, etc. These compounds can also be found in foods such as red wine, juice, cream, etc.

03Mena Reaction​

Recently, more and more coffee shops have set up roasters at the door of the store to roast their own coffee. This not only saves costs,

The Mena reaction can be divided into three stages

1. Initial stage:

Amadori molecular rearrangement of carbonylamine condensation

2. Mid-term:

The Amadori molecular rearrangement product fructosamine is dehydrated to HMF (hydroxymethylfurfural)

Fructosamine deamination to form reductone

The interaction between amino acids and dicarbonyl compounds

3. Terminal stage:

Polymerization reaction of melanin by aldol condensation

Coffee is blessed with a large and complex variety of chemical substances. In addition to the compounds mentioned above, there are other organic acids, inorganic acids, alkaloids, etc. The sweet and delicious ingredients and slightly bitter compounds give the coffee flavor a wider range of levels and changes, creating the unique rich taste of coffee.

During the coffee roasting process, the caramelization reaction causes the sugar in the coffee to oxidize and brown, while the Mena reaction causes amino acids to react with sugars. The sequence of these two reactions is the secret to the charming aroma of coffee.