In class, in order to let students learn to distinguish the taste of bad coffee, we often take some bad beans or baked beans from some places of origin as examples to brew. As a result, many students said, "Hey, it tastes the same as what I used to drink …". Obviously, some coffee on the market is problematic, but if it has not been studied, it is hard to say. This is why I later developed cold extraction. By cold extraction, we can more easily judge whether the coffee is bad or not.

As for how to tell whether beans can still be drunk, it is really difficult to explain in detail here, but at least one thing is clear. When the oil consumption of beans comes out, I will never drink it again.

In addition, sometimes beans will be moldy and difficult to distinguish with the naked eye. I can teach you a test method: first grind coffee beans into powder, then pour hot water into a cup, then pour all the water out, dry the cup, then quickly pour coffee powder into the cup, cover the cup mouth and pick it up later. If there is a musty smell at this time, even if there is only a little musty smell, don't drink any more.

The accuracy of this method is very high, because sometimes the coffee bean looks roasted, but in fact the core of the coffee bean is not cooked, and there is too much water left in it, so of course the beans are easy to be moldy, but you can't feel that there is something wrong with the coffee bean by visual inspection or extraction, but you can easily force out the musty smell by the way I mentioned just now.

(This article is taken from/Right Coffee Science/Dialect Culture)