Freshly roasted coffee, or coffee from freshly ground beans tastes so much better than drip coffee made from vacuum packaged coffee. Why is it so different?
Coffe is a natural product, and has a shelf life. The changes made to store the product for a longer period, makes the coffee deteriorate.
Coffee is at its best one week after roasting, and the shelf live is maximum 3-4 weeks after roasting. If the bag of coffee has a ‘best before’ or ‘use-by date’ rather than a ‘roast date’ it’s because whoever packaged the coffee would rather you didn’t know when it was roasted.
Three words: volatile aromatic compounds. There are well over 800 aromatic compounds found in coffee and they are volatile because they evaporate at room temp.
You can readily understand this if you open up a bag of fresh roasted coffee beans. Smells wonderful. Then grind up those beans and the smell is increased many times. The grinding releases the aromatic compounds. But at this point, the aromatic compounds are evaporating at a greater rate then if they have been left as whole beans. In addition to aromatic evaporation, the grind (and even the whole beans) are being exposed to oxygen which begins to oxidize the bean oil - just as cooking oil can go rancid, so can coffee bean oil.
This all starts happening once beans are roasted and it is increased considerably once those beans are ground.
As far as vacuum packing goes, I've read that due to carbon dioxide out gassing of the roasted bean, factories leave beans out till the out gassing stops and then vacuum pack the beans (ground beans more then likely). Then some if not most of the aromatic compounds were already gone. Vacuuming packing does make roasted coffee last longer, but it's probably not the best the coffee could have been.
Look, even though I've been roasting coffee for myself for the last 15 years, I'm still a layman trying to make sense of and trying to explain what is a really complicated subject.
All I know is, buy whole roasted beans that have a roasted date stamp within a week of your purchase and you'll be laughing.