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Let me preface by saying I clean my machine every day. I only use filtered water. Machine: Morphy Richards Fresco (Standard drip-coffee)

I use coffee grounds (medium roast). I don't know the grind. I buy the grounds from a local coffee shop.

When I make four cups (max capacity). basically filling the grind in the metal filer to "4-cups" mark (max).

, 3/4 of the way: The coffee pours at a reasonable rate till it becomes extremely slow. Only drops are coming out. Then finally like a pressure cooker, the coffee pours out a rapid rate. It has a sort-of burned smell to it. The coffee still tastes good.

The same does not happen when I fill the filter for 3 cups.

I find the 3-cup brew slightly less bitter, it has greater natural sweetness.

I can not tell why.

UPDATE: I found that this was much more prominent in my coffee which had chicory.

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  • It's possible that the grind is too fine. As Tyler Hartwig's answer describes, the coffee can pack too tightly or clog the filter, causing the slow down. If you're brewing at max capacity, the water can then overflow the filter, giving you the sudden increase in flow.
    – fixer1234
    Commented Jul 2, 2022 at 20:36

2 Answers 2

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Not sure if you'll be able to get a definitive answer on this one, but to me it sounds like filter/coffee choking, and then somehow un-choking. This is something I've experienced with pour-over brews. I've used my Fellow Stagg [X] Dripper before, and at 15g of coffee it's perfect, however at 24g the weight of the coffee is too great and it presses the filter and coffee directly against the holes on the bottom of the dripper.

Throughout the process I'll give the coffee a few stirs with a stir-stick, and it will immediately start flowing faster. It makes sense that you'd get a sweeter more balanced cup when the coffee doesn't choke. To me it also makes sense that you have a greater chance of it choking with more beans. Not sure how it could un-choke by itself, one theory is that once enough water pressure is present it creates a low-resistance channel where water flows through very quickly (and this water doesn't extract much coffee, rather would mostly dilute in this case).

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  • I suspect the same. I found something interesting though. The local coffee grounds have chicory and this tends to clog up more than your plain "medium"-roast grounds. The chicory one is somehow sweeter.
    – Dhruv Pandya
    Commented May 13, 2020 at 18:56
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this may be a feature, not a flaw. some coffee makers these days hold the water until sufficient pressure builds to allow the coffee to brew before draining (some call this "dwelltime" afaik). just a thought; no idea how your particular maker works.

moreover, it's common when making coffee by hand to pre-infuse your grinds with water to allow the CO2 in the beans to off-gas. this is done by wetting the grinds just enough for them to get wet, without actually draining through to the urn. your maker might have a pre-infusion system built in as well. some fancier espresso machines a have automatic pre-infusion presets.

if it's neither of these, it could be the coffee naturally blooming in the filter. especially fresh coffee takes on a lot of water before it starts to brew, which would create a hysteresis effect, but probably not as noticeable as you're describing.

edit: sorry i misread your post and see now that the slow-down happens 3/4ths of the way through. i'm afraid my answers don't account for that but i'll leave it up in case anyone happens to find it useful/interesting. to me this sounds more like a clog that gets pushed through when enough water pressure builds up.

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