Double filter with a chemex causes bypass

Coffee preparation techniques besides espresso like pourover.

#1: Post by DamianWarS »

I was using a standard cone filter with a small Chemex and after I got it wet and added the grinds I noticed there was a slight tear in the paper which would cause grinds to come out. nothing had really happened but since the filter was wet I didn't want to try and dump the grinds out into another filter since a bunch would probably stick on. So I just used another filter under it as a double layer which at the time I thought was the best option. As it turns out the extra layer caused the drawdown to be twice as fast which you would think is counterintuitive. But I understood what was going on right away and thought it was something interesting to stumble upon.

It's about bypass. since the Chemex has smooth walls the paper filter seals to the wall and allows for very little bypass which is water traveling between the paper filter and the walls (thus bypassing the coffee bed). Ridged surfaces don't have this design such as the V60 as the ridges function to lift the paper off the walls and prevents a seal from happening allowing water to pass between these spaces (wave filters accomplish this by the paper design). Since I added a double filter the bottom one was sealed to the walls from prewetting but the top one had already been prewet and I just placed it inside with the coffee already added. The filter with the coffee never did seal and the result was the drawn down was twice as fast.

I normally grind coarse for the Chemex which ended up probably making the drawn down even quicker since I wasn't planing for a bypass style of brew. I'm not sure if I would deliberately do this again but if all you had was a Chemex it's useful to know you can get V60 like profiles from it with a double filter method like this, you just got to make sure the top filter doesn't seal. I just thought it was interesting and proves the difference between bypass and bypass-free methods. I've seen people try toothpicks to do the same thing, and altough this could be argued as wasteful (since it uses 2 filters) i would be a lot easier than setting up toothpicks.

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#2: Post by yakster »

Some have used glass rods bent to the shape of a candycane.

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DamianWarS (original poster)

#3: Post by DamianWarS (original poster) replying to yakster »

glass rods would work much better than toothpicks. I get 2 filters are more wasteful but it would be a lot easier to source and set up than glass rods. a silicone sleeve insert that adds the ribs to the walls would work too, I'm not sure if one is marketed for the Chemex or not or if you could get a silicon pour-over cones and just insert that. I'm surprised there isn't more ad ons to the Chemex like this, Lance Hedrick in his Chemex Brew Guide suggests using silicone cut out to fit over the channel to ensure the channel is kept open so why not just make an entire silicon sleeve for the chemex, one with ribbs and one without marketed at upgrading the chemex. if you don't like silicone, wire mesh would do the same thing not for filtration but acting as something that lifts the paper off the walls.