hornbyben OK, so the experiment was carried out as follows:
Beans: Coffee Compass Malabar Hit Mahogany Roast (medium/dark). 500 gr. bag roasted 3 October, opened 15 October morning and split into 2 equal parts. One poured directly into hopper, one left in original bag; bag carefully wrapped closed to reduce air inside, secured with two elastic bands and put into freezer immediately.
The ‘new’ beans were taken out of the freezer and poured into the “closed” hopper immediately. Condensation formed outside the hopper, but the beans were dry. They were at ambient temperature by the time I pulled the second shot.
Last shot of the first half bag - 17.1 grams
Cleaned grinder - including using “bellows” and running empty for 10 seconds
Purged with new beans in hopper until flow of grounds was regular
First shot of the new bag - 16.9 grams at same grinder setting.
WDT and my ‘normal’ tamp for both shots into an IMS 14/18 grams basket.
Both brewed at 91.5 °C group / 97.5 °C boiler, 12 seconds pre-infusion @ 2 bar, into 42 / 43 grams of liquid. Curiously for me, the second shot ran a bit faster, but the first had a couple of drops in the cup at 12 seconds, the second was ‘dry’ until I released the lever. Basically, I would say that any differences here are due more to differences in prep than anything else.
“Last” shot
“First” shot
By the time I got to tasting, the first shot had cooled quite a bit and the crema was partly gone. Both were recognisably the same coffee - bittersweet chocolate, with spicy notes, a bit of burnt orange (?) and good body. The ‘fresh’ shot did taste fresher and more complex, but it may also have been the temperature. When I cut both with 20 grams of steamed milk, the impression reversed, and the ‘old’ shot tasted marginally better (a bit more ‘bitterness’ cutting through the milk sugars).
My wife and son also tasted both cups (black and with milk), and confirmed my impressions: small but perceivable difference in favour of the ‘new’ beans when black; a bit more bitterness in the ‘old’ ones when cut with milk - which we all found agreeable.
In summary - yes, there is a difference after 4 days. Would we have noticed without the back-to-back? Probably not, and the coffee remained very pleasant to taste.
I may try to split the next bag into 4, and run ¼ each in the steel pipe, with far less air and light than in the hopper and half the “open time” - after all, it’s exactly the same cost and workflow, other than opening the freezer 2 more times.
Whether all this says anything for, against or even about single dosing… I don’t know.
Thank you for suggesting the experiment!