I was reading a recent reply to a post and it said to leave your pf empty (basketless) when you warm up your machine. I've always left my basket in during the warm up. Am I doing it wrong, and why does it make a difference?

Jay

I don't think it matters, as long as you're consistent (i.e., dosing in the basket or dropping in). Since this seems relevant, below is my post excerpted from Does temperature loss from dosing basket outside portafilter matter?

HB wrote:Years ago I did measure the temperature difference between the top and bottom of the puck for hot/cold baskets:



The distance between the lines indicates the cold/hot basket delta; the distance from the 0 axis represents the top/bottom delta. It shows that indeed cold/hot baskets do have a measurable effect on the first seconds of the delta between the top/bottom, but the effect falls below the boiler's natural temperature variance shortly thereafter (measured on a La Marzocco Linea without PID controller). That said, I don't consider the above chart the last word on the matter, as it was hastily created from just a few trials back in 2004 in response to a discussion on CoffeeGeek.

Wow, you guys are serious. Then again, I did reply....
I would have tossed this one off with a hand-wave at the relatively puny thermal mass of a basket. But if I understand the question, the real alternative to basket drop-in is an even longer period during which the entire portafilter is removed for DDT (dosing, distribution, tamping), dissipating perhaps more heat than the basket ever held.

The basket itself would have little impact on the thermals but a cold portafilter has a dramatic effect. I have tested it before but dont have the data from the datalogger. Once the cold portafilter was locked in, a matter of seconds later the group head temperature started to drop like a rock by several degrees. Keeping a cold portafilter around when you have a direct attached group lever machine is a nice way of cooling the group after a couple shots. Most machines will overheat very fast after two shots but the cold portafilter would suck several degrees out of the group and let you get a 3rd shot. There is no real reason to keep the basket out of the portafilter for the coffee's sake. I have seen where people were concerned abut the hot basket burning the coffee as it was dosed into the basket but they dont get that hot.