In my, somewhat limited, experience with espresso machines they generally only produce a few shots of espresso per load.
Is this a technical limitation of espresso making or is it just that the manufactures expect normal, healthy, people to only drink a shot or two at a time?
To put it another way:
Are there machines out there that are capable of producing a pot of espresso or does the process require small batches?
The key here is extraction from the espresso coffee. Only so much desirable flavor and body can be pulled from a puck of coffee. So, then you might say, why not make the puck bigger? Well then that would force the water through a thicker puck, causing the extraction to be slower and longer, giving bitter flavors. The amount of pressure needed to make a desirable "pot of espresso" with a larger "puck" (or probably more accurately, a "slab" in this case) would be a wild safety hazard, since the pressure would be too immense for any cost-effective equipment to handle.
So, is it a technical limitation? Yes and no. I think it has more to do with being a tried process that gives repeatable, scientific results.
The volume of espresso that your machine makes, is limited to the size of it's boiler and it's ability to replenish, heat the water, and deliver the force to brew the espresso. Working on commercial machines, I've seen boilers last 5+ minutes before losing temperature. With such a machine, your coffee would probably run out of desirable flavor before you'd make a full pot of espresso.
The biggest machine I've worked with is a 4 group LaMarzocco Linea which could produce 8 shots at once (after you prep and pack all 4 portafilters). So 8 ounces with a lot of effort.
But it's also customary to drink espresso in smaller quantities than other kinds of coffee because it's so highly concentrated: you don't need as much to feel the effect.
