Choose fresh coffee beans. When purchasing, pay attention to whether the color of the beans and the size of the particles are consistent. Good coffee beans have a shiny appearance and a strong aroma without any odors. Regardless of the type of coffee beans, freshness is an important factor affecting quality. When making a purchase, grab one or two coffee beans and chew them in your mouth. They should be crisp and sound (indicating that the coffee has not been dampened), with a lingering aroma on your teeth and cheeks. However, it is best to pinch them by hand to feel if they are solid, rather than buying crispy coffee. If the coffee beans have lost their aroma or smell stale, it means that the coffee beans are no longer fresh and not suitable for purchase.

Freshly stir fried coffee beans are not suitable for immediate consumption and should be stored for a week to completely release the gas inside the beans.

The deliciousness of coffee lies in its aroma; And the aroma will start to dissipate at the moment after baking is completed. No matter how expensive the coffee beans are, if they are not fresh, the taste will be greatly reduced. Andrea Illy, the current leader of the old Italian coffee brand Illy, has a detailed article in her book Espresso coffee: the science of quality, detailing the impact of coffee bean "flavor" and different packaging methods on quality. Each kilogram of coffee beans, in an unsaturated environment, will release approximately 6 to 10 liters of carbon dioxide, equivalent to 1% to 1.2% of the total weight of the beans. Thirty five percent of it is discharged in the first three days after baking. And with the release of carbon dioxide, there is also an equal amount of volatile aromatic compounds. That is to say, there are some flavors that will dissipate if not consumed within the first 3 days after stir frying coffee beans. The author further mentioned that stale beans not only lose their good taste, but also create a bad taste. The compounds inside the beans are affected by oxidation, and the taste becomes negative. So coffee on supermarket shelves usually has a slight oily taste. Because it usually takes several months from baking, importing to shelving in foreign countries. The 'flavor appreciation period' (note: not the expiration date) has long passed.

　　Generally speaking, the best drinking period for coffee is one week after stir frying, when the coffee beans are freshest and the aroma and taste are best expressed.

　　In addition, the purity of coffee beans is another factor to consider. When choosing coffee, experts do not necessarily look at the size of the particles, but rather grab a handful of individual coffee beans (Regional Coffee), about dozens of pieces, to see if the color of each individual bean is consistent, and if the particle size and shape are similar, in order to avoid buying inferior products disguised as mixed beans. But if it is blended coffee, differences in size and color are normal phenomena. In addition, heavy heat and medium deep roasting methods can cause coffee beans to produce oil, but if the beans are lightly roasted and produce oil, it indicates that they have spoiled, not only reducing their aroma and richness, but also causing astringency and sourness. In short, when choosing coffee, attention should be paid to its freshness, aroma, and whether it has aged or not, and the ideal purchase quantity is to drink it within half a month.