Did you know it's possible to brew coffee to early? Whilst as a fresh food product it's well known coffee can go stale, and it's generally advised to buy fresh, what it the coffee is too fresh? When coffee is roasted, it goes through a whole myriad of chemical changes; one of the primary chemical releases being carbon dioxide. Coffee generally degasses mainly carbon dioxide very quickly over the first few days after being roasted. One of the main expressions of any brewing type is carbon dioxide release whether in the form crema on espresso, or the bloom on pour over coffee.
To mitigate an overreaction and big release of carbon dioxide, it's worth resting your coffee for at least 3-4 days from roasting. The main brewing method of concern is espresso. If there is too much carbon dioxide in the coffee, high pressure hot water can create too much chaos and problems achieving a consistent brew. Usually there will be too much crema, and flavour problems. For other brewing methods like French press and pour over, you will notice the a bigger layer of bloom with more carbon dioxide releasing. Keeping to this 3-4 days rule ensures a more even release of carbon dioxide.
