Espresso: Freshness - Fresh? Too Fresh?
The freshness issue for espresso is different than for other brew methods. Over time, I have come to believe that homeroasted espresso needs a lot more age on it before extraction, more so than infusion and drip brewing techniques. Carbon dioxide rapidly degasses from coffee in extraordinary volumes after roasting, especially in the first 24 hour after roasting. During this time, espresso will be less flavorful and thin. Gas emerging from the coffee will prevent water from thoroughly percolating through the grinds, resulting in underextraction. You will notice fast brew times and light-colored crema. It will also have a specific taste from the gas, a tingly, baking soda effect (not the flavor of baking soda, but that effect). This unpleasant taste can persist for up to 72 hours in my experience, and it depends on the degree of roast, and the specific coffees in the blend. You can rush the degassing process by grinding coffee ahead of time and letting it sit a few hours; a coffee "sin" by all measures, but sometimes we all get desperate!
If a specific type of coffee or type of roast doesn't agree with you, let it rest in a sealed glass jar. Sometimes after 5 or 7 days it turns a corner and becomes quite wonderful, but after 10 to 14 days it will degrade as it moves into staleness. And sometimes as little as 10-20 seconds difference in roast times has a huge effect on the espresso, so don't bash a coffee until you have tried it under a range of roasts.