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Ah great post, and good to know, thanks MrJack!! Yeah must be more variables involved for sure... what are your thoughts on clumping, and whether that has any effect on density within the basket? You would think that any clumps would be 'tamped out' when tamping, but not too sure, seems like clumps are still high density/concentrated balls within the puck that may not get squashed or spread out during tamping... and I'm really thinking clumping affects how well you can effectively distribut too... (ie how the grinds move around/slot around each other when tapping the side of the basket for example...)Originally posted by MrJack View PostTry watching some slow motion espresso shots on youtube (you can slow them down further with the video settings). Even for shots that look very even at normal speed, the espresso almost always appears at the outer edge of the basket first when you see it in slow motion.
I have a few ideas as to why this happens in espresso pours (relating in part to basket shape and grinds distribution). It is consistent with studies of flow in other kinds of packed beds, which typically show higher velocity flow at the perimeter and mostly uniform velocity everywhere else (unlike laminar flow in a pipe, which is fastest in the centre).
In my experience it is exacerbated in very tight pours - so I would expect grinding finer, over-dosing and very firm tamping would make this worse. Slower flow is the result of greater resistance (also caused by those three factors), hence the correlation between the two.
The flow outside of the basket is dominated by the competing effects of gravity, viscosity and surface tension. If there is not sufficient (or any) flow through the centre of the puck (relative to at the perimeter), then the stream won't come together in the centre.
Edit: Here is one I prepared earlier...
And awesome vid! Watched that awhile ago, didn't realise it was yours! Really cool to see that the flow still starts around the edges.
Hahaha what the! Love it... Still on topic, still on topic [emoji14]Originally posted by Yelta View Post
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After much experimentation... and lowering the dose to get a normal 1:2 ratio shot, WDT just seems to dominate...
Am just getting really great results using it.. It's not too much extra time taken, but I'd like to find a way to get the workflow faster if anyone who uses it has any suggestions.
When I try to pull a double ristretto it doesn't seem to get want to come to a central pour (by double ristretto I'm talking a 1:1 ratio, ending it at about 35 seconds), but it just didn't seem to matter tastewise. Using WDT and the shot just looked fantastic, and tasted incredible.
Changing back to a coarser grind and getting a 1:2 ratio it went central fairly early into the pour.
Anyways, am loving the results of using WDT (after MANY years of me saying, "no no, I never want to go that far" haha).
I'm also realising that distribution doesn't necessarily have to be set in stone, and needs to be flexible based on the coffee. The previous bean I used I didn't need to do WDT, but this bean which is a medium-dark roast it has been helping heaps.
I reckon the skill of the barista is to note and adapt to these changes, and I think the intuitive and art aspect of coffee comes into it. For awhile I kept getting stuck in certain models or ways of believing I had to do things, but I'm thinking there is no 'one size fits all' distribution technique. It really really really depends on the bean and those particular conditions!
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