Extraction and temperatures on frozen coffee beans - Page 2

Beginner and pro baristas share tips and tricks for making espresso.
PIXIllate
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#11: Post by PIXIllate »

Jake_G wrote: When I freeze beans, I often pull straight from the freezer and grind frozen. Doing this requires a slightly coarser grind than letting the same beans come to room temp prior to grinding, but I can detect no difference in the cup once the shot times are equalized with the grind setting.

- Jake
This mirrors my experience. I like to have some decaf on hand for the odd after dinner shot. Since decaf will require a finer grind setting I'm often able to get it to flow normally without adjusting the grinder when it's frozen and my non decaf isn't.

Milligan

#12: Post by Milligan »

Today I pulled frozen beans out from my freezer and used them for a pour over. By the time I weighed them, ground them, let them sit for a couple of mins in the dose cup, and dumped them into my preheated V60 they were around 55F. Room temp is 70F in my house. That is a 15F difference.

Using Rao's formula in his Barista handbook then that would account for roughly a 2.5F drop in temperature if you mixed a slurry of 2:1 ratio water to coffee grounds with a 15F temp differential between room temp and what I measured earlier from frozen. That is not a real brew temp. The actual brew temp would be less of a difference due to the portafilter and group head mass as well.

Formula I used is:



Mc = Mass of coffee, sc = specific heat of ground coffee (0.4), Tc = Temp of coffee, Mw = Mass of water

This was derived from Rao's formula in The Professional Barista's Handbook. I used 16g coffee and 32g water with the two temps of 70F vs 55F. Of course there could be an error in here somewhere, I'm only one coffee in this morning. :lol:

jpender

#13: Post by jpender »

Milligan wrote:That is not a real brew temp. The actual brew temp would be less of a difference due to the portafilter and group head mass as well.
The formula in Rao's book is very simplified. It's not just the effect of the portafilter, it's also the fact that you don't start out with an equilibrated slurry: the temperature will be dynamic. There is also a small but significant amount of heat generated by the mixing of coffee grounds and water that he did not take into account. For that matter the specific heat of coffee isn't well documented. Rao did not provide a reference.

All that said, an effect on the order of 1°C probably isn't going to make enough of a difference. Is your espresso machine even that thermally stable? I'd put my money on the grind characteristics of warm versus cold coffee for whatever differences one measures or perceives.

Milligan

#14: Post by Milligan replying to jpender »

Agree on all points. The fact that even in the most restricted case there is only a 2.5F difference means after all factors are considered it would be very insignificant. This also assumed all water going in would come out, which is not the case. I believe there is something like 1g of water per 1g of grounds retained in the puck. So total water introduced to the grounds would be 48g instead of 32g then also the water that is back flushed... Again, these are just rough numbers. The key is even at the most basic hypothetical without taking into account all factors there is only a 2.5F difference in brew temp which would be barely perceptible. I would wager the true difference in brew temp would be in the low tenths of a degree F after it is all said and done.