I was recently told by Breville that to get a good pressure during coffee extraction I should only use beans with a 'roasted on date' and not beans purchased ar supermarkets as they could be only and will lack the oils present in freshly roasted beans. I did read somewhere that roasted beans are best used within 3 weeks of roasting.
But how much does this affect the pressure during extraction?
I was using Vittoria beans and even using the finest grind setting on the inbuilt burr grinder could not get pressure higher than the 'pre infusion' area (eg underextracted).
What coffee beans purchased from supermarkets are best for use in $800 home espresso machines?