I have seen the effects of locking a cool PF on my group temp and the effect is surprising but with my crummy technique, I know it didn't affect my shot at all


Sean

lennoncs wrote:I have seen the effects of locking a cool PF on my group temp and the effect is surprising

but, in that case, you've introduced a heat sink. i would expect a bit of a cooldown then, although at a slower rate than most folks expect (the conductive transfer points are fairly small).

malachi wrote:You heat the portafilter up.
Then it cools off again as you dry it.

It cools off if you don't heat it up too, and a dry-wipe takes 0.5 to 1.5 seconds. If you heat it up, it'll end up at a higher temperature when you're pulling the shot... no?

I'm still not clear on what effect taking the PF away from the group head has on the temp that the coffee sees.

So far I've seen two measurements for the portafilter, Andy's and Barry's posted earlier in this thread.

They do not show the same result, but both agree to-

• 1. 10-20 degree F heat loss over a minute.
  
  2. 5-10 degree F heat loss over 30 seconds.
  
  3. ? degree F heat loss in the first 5 seconds. (Andy says rapid temp drop, Barry's chart shows no change)

The three time frames roughly correspond to 1. A leisurely grind, dose and tamp into the portafilter. 2. Quite fast dose and tamp into the portafilter. 3. Taking out the pf only to drop in the filled basket.

According to Abe Carmeli and Barry (earlier in this thread) the group head would not cool down much. A little heat would be drawn from it when the now-cooler portafilter was re-attached, perhaps negligible?

I'm thinking the next step would be to measure (how?) the effect on the temperature of the brew water (or coffee puck) as the portafilter warms up again.

Sorry I don't have the tools or know-how to help with this, but I would love to see the results! Although at the same time I am thinking that most people have figured out how to compensate for this . . . the important thing being a constant routine.

Henry

hbuchtel wrote:I'm still not clear on what effect taking the PF away from the group head has on the temp that the coffee sees.

After the coffee emerges from the bottom of the basket... and before it hits your (hopefully preheated) cup.

Again, negligible with a crotchless/naked portafilter... but not with a "normal" spouted one.

hbuchtel wrote: 3. ? degree F heat loss in the first 5 seconds. (Andy says rapid temp drop, Barry's chart shows no change)

actually, the chart shows immediate change. i just forgot to mention that the pf was pulled 10 seconds in (iirc). i usually let the datalogger run for at least a few seconds to establish the baseline condition. sorry for the omission.

hbuchtel wrote:I'm thinking the next step would be to measure (how?) the effect on the temperature of the brew water (or coffee puck) as the portafilter warms up again.

i have some data on the puck. i'll try to look up the details this evening. sorry, it's really the wrong time of year for me to be doing this.


--barry "roasting in a mall"

Barry, when you have time can you post some of the warming/cooling portafilter test results that you mentioned earlier in the thread?

Much appreciated,

Henry

barry wrote:i'm not sure the group cools significantly when the portafilter is removed... there's no doubt that heat radiates from the showerscreen, but that happens with or without the portafilter in place, so i guess for there to be significant cooldown the rate of heat loss through the showerscreen would have to increase with the portafilter removed. i'm not sure that happens.

Funny, I always kept thinking that heat transfer is proportional to ΔT. And that would make for a big difference for the group whether or not the PF is on or off (roughly some 40°C)...

recall that the portafilter radiates heat to the atmosphere, so with the portafilter installed the group heat loss is group + portafilter. removing the portafilter may or may not increase the heat loss (more direct radiation to atmosphere, but smaller total surface area radiating).