I get up every day and have a cup of coffee as usual, but when I open the bean can, I find: "Oh my God, didn't you just buy these beans??" How is the oil whirring? Can this still be drunk? ”
Don't rush to take pictures and send them to Moments, some freshly roasted beans, it is normal for "oil" to come out after a few days, sit down, and let the front street give you a detailed chat about the "oily" surface of coffee beans
What is this layer of "oil"? The more oil, the less fresh the beans?
Sometimes we can see a thin layer of oil on the surface of coffee beans, but in fact, the "oil" evenly spread on the surface of the beans is essentially a water-soluble fat.
During the roasting process, the internal tissues of green coffee beans swell and produce carbon dioxide, which is saturated with the aroma and oil of coffee. When the coffee beans return to the room temperature and pressure environment from roasting, they begin to slowly discharge carbon dioxide outward, and the aroma substances and oil in the coffee are also discharged together, the aroma dissipates in the air, and the oil stays on the surface of the bean, which is the reason for the oil output of coffee beans.
In fact, the degree of oil yield is closely related to the degree of baking. Because as the roast deepens, the looser the internal structure of the beans beans, the higher the carbon dioxide content. As a result, the deeper the beans are roasted, the more carbon dioxide is emitted, the more grease permeates out, and the oilier the surface. (The deeper the roast, the easier it is for the surface to get oily.) ）
For example, the Indonesian ** Mandheling coffee beans in Front Street belong to medium to deep roasting, and the beans will be shiny after 3 to 5 days, which is a normal phenomenon.
Of course, medium-light roasted beans will also have oil, but it is different from dark roasted beans. Fresh shallow roasted beans are dry on the outside, and some beans that have been roasted for about 5-7 days will have dotted oil droplets on the surface, which is due to the phenomenon of local dehydration due to uneven heating, and these dotted oils represent the best tasting period of coffee.
However, if the surface of the shallow roasted beans after a few weeks will have a layer of oily luster, and the aroma will be very weak, with a slight greasy taste, it means that the flavor of the coffee beans has been lost, and it is recommended to drink it as soon as possible.
Therefore, the degree of oil produced by the coffee beans can only be used as a simple basis for judging whether the beans are fresh or not. It is important to know that the performance of coffee is mainly due to the loss of carbon dioxide in the body, accompanied by the dissipation of flavor substances.
The actual judgment of the freshness of the beans is the most obvious in the actual extraction process, for example, the powder layer does not expand at all during simmering, indicating that the gas in the beans has been exhausted; During the extraction process, no aroma is released, the taste is empty, and there is an unpleasant flavor such as wood when drinking...
If you want to keep your coffee beans fresh for a long time, you still have to store them properly.
While oiliness on the surface of coffee beans is a normal part of the flavor season, if you don't store your beans properly, you're "self-defeating".
This is because the beans will come into contact with the air during each brewing process, which will cause the oxidation and deterioration of this layer of oil in the long run, which will accelerate the "aging" of the coffee beans, and even produce an unpleasant flavor into the coffee, destroying the flavor display of the whole cup of coffee.
Therefore, it is best to use a bag with a one-way exhaust valve or an opaque jar to seal the coffee beans, store them in a cool place properly, drink them, and then take them out and grind them to brew.
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