Where does the coffee aroma come from? How does coffee taste sweet and sour?

Baking is the most attractive part of the coffee industry. Coffee beans are almost tasteless and taste directly with a rather unpleasant vegetable flavor, but after baking they are transformed into unbelievably aromatic and complex coffee beans. The smell of freshly roasted coffee and ripe beans is refreshing and tastes delicious.

Fast or slow? Shallow or deep?

In short, the roasting of coffee refers to how dark the final color of the coffee beans is (light or deep roasting) and how long it takes (quick or slow). It is not enough to understate that a certain kind of coffee is lightly roasted, because the coffee may be stir-fried quickly or slowly, and different roasting rates can lead to very different flavor performance, although the colors of the beans look very similar.

Coffee undergoes a series of different chemical reactions when it is roasted, many of which reduce its weight and, of course, cause water loss. Slow frying (roasting in 14 minutes and 20 minutes) will have a higher weightlessness ratio (about 16% to 18%), and fast frying can be completed within 90 seconds at most. For a relatively expensive cup of coffee, slow frying will show a better flavor.

During the roasting process, three factors that determine the final flavor of coffee must be properly controlled: sour, sweet and bitter. In general, the longer the overall baking time, the less sour it leaves. On the contrary, the bitterness increases with the increase of baking time, and the deeper the roasted coffee is, the more bitter it will be.

The development of sweetness shows a bell-shaped curve, between the peak of sour taste and bitter taste, and good coffee roasters know how to make coffee beans reach the sweetness peak in each roasting degree. But whether you use a baking method that is both sour and sweet, or a baking method with extremely high sweetness and relatively weak acidity, adjusting the roasting method may not help if the quality of the coffee beans you use is poor.

Sugar in coffee

Many people refer to sweetness when describing the flavor of coffee, and it is important to understand what happens during baking to produce these natural sugars.

Coffee beans contain a certain amount of monosaccharides, although not all sugars are sweet, but these monosaccharides are usually sweet and easily react under the catalysis of coffee roasting temperature. Once most of the water in coffee beans evaporates, sugars begin to react differently with calories, some of which produce caramelization, making some coffee beans caramel-like. In particular, the sweetness of caramelized sugars decreases and eventually becomes one of the sources of bitterness; in addition, some sugars interact with proteins in coffee beans to produce the so-called Maillard reaction (Maillard reactions), which also includes the browning of meat in the oven and the discoloration of cocoa beans when baked.

When the coffee goes through the first explosion stage, the monosaccharides almost do not exist, they may be involved in a variety of different chemical reactions, and eventually transformed into more different types of coffee aromatic compounds.

The acid composition in coffee

Coffee beans have many kinds of sour taste, some taste pleasing, some are not very delicious. For bean bakers, one of the most important acids is chlorogenic acids (CGAs for short). When roasting coffee, a key goal is to completely remove the acid that is not delicious enough, while avoiding creating more negative flavor factors and retaining more pleasing aroma components. In addition, some acids remain stable after baking, such as quinic acid (quinic acid), which adds a pleasing, clean coffee flavor.

Aromatic compounds in coffee

The aroma of most coffee comes from three major reactions during coffee roasting: Maillard reaction, caramelization reaction and Stryker degradation reaction (Strecker degradation, another reaction related to amino acids). These reactions are catalyzed by heat during coffee roasting, resulting in more than 800 different volatile aromatic compounds (aromatic compound), which are the source of coffee flavor.

Although coffee has much more aromatic compounds on record than wine, the same kind of coffee bean has only some aromatic compounds. Many people want to synthesize the aroma of freshly roasted real coffee artificially, but it ends in failure.