Burnt espresso flavour

[Johnlyn]

So usually I hit a coffee session in the morning and shut things down. But every now and then I leave the machine on and hit up another shot about an hour or two later. I have to now confess that that shot usually tastes slightly burnt and I am not sure why.

I have left the old puck in. Should I be cleaning it out before letting the machine sit?

I usually run a blank shot first for temp stability. Should I run two like I do first thing in the morning?

Any other ideas from those that leave their machine on all day?

Cheers,

[MDL]

I always clean out my puck after each shot. It seems like a bad idea to leave old coffee to bake in the portafilter?

Regarding flushing I would suggest that you should use 2 flushing shots when you go back to the machine if you use two when you start. Why would you expect the machine to be idling in a different state?

[Johnlyn]

It makes sense, just wanted to confirm with someone who does so. for some reason I thought it would idle cooler and I assume it is idling warmer due to the burnt flavour (though that may be the puck).

Cheers,

[chas]

Even though it would make for a sour cup of coffee without some warm up flushes, the group stays at about 180F even when it's been sitting for hours. That will certainly bake any coffee left in the PF.

[Johnlyn]

Thanks Chas, that does make sense. Today I experimented by cleaning the portafilter and screen after the morning session and then leaving it on. A couple of flushes later and sure enough, the afternoon espresso tasted as it should. I really appreciate this forum to think out loud and get feedback from others. Thank you.