Why does coffee smell so good? Why is the aroma so strong when grinding coffee?

Caramelization reaction

Once I ordered a cup of Guatemala-Huehuetenango near the Kaohsiung Cultural Center and spent a beautiful afternoon with "my Adventure" (My Life As An Explorer by Sven Hedin). After drinking coffee, I accidentally found that the dry coffee stains at the bottom of the cup were arranged into interesting patterns. I picked it up to see if I could see the jackpot number of the next big lottery. I didn't see the first 15 for a while. I think the patterns are more like an explorer marching among the rolling brown sand dunes in the desert. All of a sudden, the sweet smell of caramel flashed for a moment, and then smell it carefully, the sweet smell of caramel came from the bottom of the cup. Isn't the tiny Nanguo I ordered black coffee? Why is there the sweet smell of caramel? Later, I found that the black coffee itself is really sweet, especially the sweetness of caramel! But the sweetness of each kind of coffee varies depending on the variety of beans and the way it is roasted.

The sugar in the coffee bean is caramelized at about 170-200 ℃, which is exactly the melting point of sucrose (185 ℃) and the temperature of the explosion stage when the coffee bean is roasted. The product of caramelization is divided into two parts:

The dehydration product of sugar is caramel or sauce.

The pyrolysis products are mainly volatile aldehydes and ketones.

Generally speaking, fire-roasted aroma, caramel and color are produced in the caramelization reaction, as well as other aromatic substances such as maltol, Cyclotene, furan and so on. These compounds can also be found in red wine, fruit juices, cream and other foods.

However, if caramel is too much in the baking process is not a good thing, but will cause carbonization, making the coffee dry and choking. If the caramel is not enough, it will make the aroma monotonous and lack of layers.

Mena reaction

Recently, more and more coffee shops set up a baking machine in front of the store to bake by themselves, so that they can not only save costs but also control their own quality. So walking on the street, you can often smell the unique aroma of roasted coffee beans, including the burning blue smoke smell of plant fibers, the sweet smell of cream, the brown smell of toast, and so on. Most of these rich flavors come from the Mena reaction during baking.

The Mena reaction can be divided into three stages:

First, at the initial stage:

Carbonylamine condensation Amadori molecular rearrangement

Second, in the medium term:

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

Deamination of fructosamine to reducing ketone

Interaction of amino acids with dicarbonyl compounds

Third, at the end of the year:

Aldol condensation

Polymerization of melanin

In addition to sugars, proteins account for about 11% of the weight of raw beans, and the amino acids contained in these proteins happen to be the raw materials needed for the Mena reaction. Mena reaction refers to amino acids and reducing sugars (glucose, fructose, lactose, etc.) in food.) A series of reactions during heating. Mena reaction produces a variety of aromatic substances and pigments such as Pyridines, Pyrazines, Oxazoles, Thiazoles, Pyrroles. The Mena reaction plays an important role in the flavor of food cooking, whether it is the blackening and fragrance of the sausage when baking sausages, the soft roast chicken on the outside and the delicious baked bread. Mena reaction is responsible for the complete color, smell and flavor of these barbecue foods.

Coffee is blessed with a wide variety of complex chemicals, in addition to the above-mentioned compounds, there are other organic acids, inorganic acids, plant bases and so on. Not only sweet and beautiful ingredients, some slightly bitter compounds make coffee flavor have a wider level and change, together to create a unique rich taste of coffee.