I use the pressurized basket without a plug, it drains slowly with gravity pulling down the arms giving it time to heat up the piston and I figure that it's minimal water compared to filling up a large mug tall enough to heat up the piston. The pressurized basket is not as effective as submerging the piston in hot water since there's a layer of air between the water in the basket and the piston.

I've considered 3D printing something like the Thundies for my Robot.

I invert a small plastic cup, and set a small cup of boiling water on it. Very easy.

I guess that a benefit of using the plugged basket, is that you heat both piston and basket at the same time

It's a benefit, but it's a bit more complicated than that:

• At best, it's a minor benefit since comparatively speaking the thin-walled basket is not that great at heat retention -- just compare how well the heavy portafilter retains heat compared with the basket -- so you have to work fast to gain much benefit.
• Since water in the basket before the ground beans are deposited is problematical for even distribution and extraction, it should be dried before grinding; this might make the workflow more fiddly.

I don't recall if jpender did some comparative testing with heated vs. unheated basket (but heated piston and PF), but if he did, it would be worth looking at those graphs. IMHO, in principle it's good to preheat the basket for light roasts to keep heat loss from the boiled water pour to a minimum, but it should be done in a way that keeps it dry prior to the coffee going in. And more critical and beneficial to preheat the PF and piston for sure.

mixespresso wrote:I guess that a benefit of using the plugged basket, is that you heat both piston and basket at the same time

I was thinking that, but then thought that by the time you dry the emptied basket, fill it with grounds and prep it, the temps will drop quite a bit. Seems that if one is going through the trouble of heating the piston one would want to get the basket on the robot much quicker than using the same basket with a plug.

I do not preheat my robot anymore, I used to all the time. I used the pressurized basket as yakster does, though I use a string to hold the handles up as I find it makes loading the portafilter easier and at the same time it stops the slow draining of the basket.

Balthazar_B wrote:

• At best, it's a minor benefit since comparatively speaking the thin-walled basket is not that great at heat retention -- just compare how well the heavy portafilter retains heat compared with the basket -- so you have to work fast to gain much benefit.

The PF has more thermal mass but only partially contacts the basket (at the top). So when comparing a preheated portafilter (with hot water) versus a preheated basket (toweling it dry before loading the coffee) the basket preheat made a bigger difference.

That said, when I preheated the PF with the flame from a gas stove it had a larger impact than preheating the basket (with water). I don't know how hot I was getting the portafilter. Hot enough so that in combination with a preheated piston the temperature profile was flat. I couldn't figure out any problem with doing it that way but it just somehow felt like a bad idea.

Ken5 wrote:I was thinking that, but then thought that by the time you dry the emptied basket, fill it with grounds and prep it, the temps will drop quite a bit. Seems that if one is going through the trouble of heating the piston one would want to get the basket on the robot much quicker than using the same basket with a plug.

Drying off the basket takes a little bit of time and of course the temperature of the metal will decline. But it doesn't drop as fast you'd think. I did some tests where I measured the basket temperature and was surprised at how long it held onto the heat.

The other common way to preheat the basket is to pour and dump the water and then refill it. You can do it twice for that matter or a continuous pour and overflow. You don't have to dry it off but the risk is that at some point you might disturb the puck. And it does use up a bunch of water from the kettle.

jpender wrote: That said, when I preheated the PF with the flame from a gas stove it had a larger impact than preheating the basket (with water). I don't know how hot I was getting the portafilter. Hot enough so that in combination with a preheated piston the temperature profile was flat. I couldn't figure out any problem with doing it that way but it just somehow felt like a bad idea.

John, just wondering if you ever tested preheating the basket on an induction hob? I do know my Robot's basket is magnetic, so it could conceivably work. And could be an optimal approach for those who've gone induction. Well, that and boiling the water lickety-split in the most energy-efficient manner.

No, I have not. We're still using gas to cook. If we were starting from scratch we'd probably go with induction but it doesn't really add up for us to convert.

There's an increasing anti-gas push including negative press about the health risks of the emitted gases. California recently passed a law that will prevent a homeowner from buying a gas appliance starting in 2030. We just replaced our gas water heater and I was thinking that next time I'll have to go to Nevada and smuggle one in. :-)

jpender wrote:The other common way to preheat the basket is to pour and dump the water and then refill it. You can do it twice for that matter or a continuous pour and overflow. You don't have to dry it off but the risk is that at some point you might disturb the puck. And it does use up a bunch of water from the kettle.

That's what I've been doing and just realized duh, no need to pour from top, just just dunk it in water instead. I'm heating up water in a pot and not a kettle anway. I'll try and see what happens.
Sometimes I reuse the pre-heat water I pour on top for an americano so it's not always wasted (or, I pour it back into the pot if I'm using a paper filter on top, the water looks clean enough).