First of all, the original roasted coffee beans are full of gas, which is hidden in the vacuolar chamber of the coffee powder and the cracks in the cell structure. When the coffee beans are ground, some of the bubble chambers and cracks are broken, and the gas evaporates into the air (this is why we can smell the aroma).
However, there are still some gases, which can only be discharged when the water is injected, and the water travels through the cracks of the coffee powder and the deep unbroken bubble chamber through diffusion. After the gas is expelled from the beans, the space originally occupied by the gas is filled with water instead. Without the gas barrier, the water also comes into contact with those flavorful substances in the beans. The vacuoles of ground coffee contain different soluble flavors that are the subject of extraction. Water then acts as a vehicle, dissolving the soluble flavor substances in these pores into the water through dissolution.
In short, smouldering is to allow the coffee powder and water to fully contact to discharge carbon dioxide, effectively avoid the channel effect, and increase uniform extraction.
- Darker roasted coffee will produce more gas than lighter roasted coffee, and it will take a longer time to exhaust.
- The longer the roasting time is, the less residual gas is, and the waiting time for exhaust is shortened when steaming.
- The exhaust phenomenon of finely ground coffee powder will be more obvious than that of coarsely ground coffee powder.
There are many small holes in the coffee beans, where the aroma and carbon dioxide after roasting exist.
If the baking date is within 10 days, you can steam for 30 seconds, 10-20 days for 20 seconds, and more than 30 days for 10 seconds or no steaming. Light baking can be 10 seconds less than dark baking.
This steaming time is only a suggestion. There are also operations to extend the steaming time to one minute in order to improve the extraction rate. It depends on your own brewing plan.
Water has the physical property that it likes to take an easy path (where the resistance is low). If a "channel" is created in the coffee powder, the water will preferentially choose such a channel to flow, which will cause the coffee close to the channel to be extracted more; other parts will be under-extracted with too little or no water flow at all, resulting in a problem of uneven coffee extraction, which is called the "channel effect".
Hand brew extraction
The extraction order of sour, sweet and bitter
Sour substances include sweet substances, which are polar molecules and are easier to get close to water molecules, so they are easier to dissolve, or they can dissolve more under the same conditions. Bitterness dissolves more slowly in water.
Fine powders are more likely to dissolve more substances, which can help improve extraction, if without fines at all, the final coffee will tend to have a clean, uniform flavor, but the flavor may be too monotonous, so it is not necessary to completely pursue zero fine powder during extraction.
The higher the temperature of the water, the stronger the movement of the water molecules, and the greater the impact energy of the water molecules on the flavor substances in the coffee powder, which causes the flavor substances to break away from the coffee powder and diffuse into the water faster, thereby improving the extraction speed per unit time. To achieve the purpose of improving the extraction rate.
However, the difference of 1-2°C of water temperature will not have much impact on the extraction. During normal brewing, you only need to remember that the water temperature of dark roasted beans should be 4-8°C lower than that of light roasted beans. The brewing temperature of lightly roasted beans can be anywhere from 89 to 100 °C, because after the coffee powder is combined with hot water, the temperature of the coffee powder slurry will immediately drop to about 80°C.
- The hotter the temperature, the harder it is for the tongue to taste more flavors (the most sensitive temperature range of the tongue is 30-50℃);
- Good and bad tastes will be amplified at around 50°C;
- The reason why the aroma of the coffee liquid is different at different temperatures is that in the hot stage, the aroma substances are the categories that volatilize faster. After cooling, the substances that volatilize more slowly at the back end will come out;
- Not all chemicals with sour in their names have a sour taste. The biggest feature of tannins is astringency, followed by bitterness.