In Lance Hedrick's recent video on $200 filter baskets, he mentioned that using a bottom filter with a VST basket gave nearly as good results as one of those hyper-expensive baskets. This inspired me to try a bottom filter. My shots have much more clarity with bottom filters and I plan to keep using them.

Prior to using a bottom filter, I thought my puck prep was pretty good, and my extractions with a bottomless portafilter had good visual appeal. But with a bottom filter in place, the extractions look quite ugly. I have multiple streams that vary in intensity and position, and never coalesce into a single stream. I've tried with the bottom filter both wet and dry. The extraction looks and tastes better with a wet filter, but is still far from perfect. Is this normal with a bottom filter? I've seen other people report similar problems with bottom paper filters on other forums.

I started by cutting down Aeropress filters to fit my basket, and also tried some Good Brothers 55mm filters cut from Chemex filter paper. Both performed the same. I'm using an IMS BaristaPro basket. My puck prep is: grind into filter basket, WDT, tap, and tamp with a self-leveling tamper. I get a much faster flow rate with the bottom filter in place, and grind finer to compensate. I get similar results on both of my 2 setups.

I've noticed when I hold a paper filter up to the light, it looks like its density varies greatly in different areas of the paper. See photo below which is of a Good Brothers filter made from Chemex paper. Could this unevenness be the cause of the uneven extraction?

I want to emphasise that I am very happy with the shots I pull with a bottom filter, but I'd like to have a better understanding of what is really going on during my extraction.

Thanks for the help!

Can you film a shot and post it?

It's good to remember that what happens when you look at the bottomless happens after the coffee has exited the puck and therefore interpreting that is more tricky than most people think it is, especially when a paper filter changes the signal and its interpretation.

For example, the lack of merging could be something as trivial as the paper filtered shots running faster and at lower pressures and the basket not flexing as hard in the center. It could also be due to the changed flow and changed fluid viscosity over time making the coffee fall down before it merges. There are a multitude of reasons why the shots might look different to what you're used to.

Here is a video using a wet bottom filter. I neglected to start the camera until the extraction was underway. If you really need to see the beginning of the extraction, let me know and I'll try again.

GDM528 wrote:I get multiple streams - but they're all similar flow rates. In your video, it looks like the central stream is largely dominant.
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Wasn't in your video, but I see a donut ring at the beginning of pre-infusion. Then I do a very long and low-pressure pre-infusion, and don't start the shot until the entire bottom of the basket is fully wetted.

I tried a long pre-infusion, and my results were similar to yours. I started with a donut extraction. When I increased the pressure i got 3 equal streams. The shot tasted a bit bitter, probably due to the lengthy pre-infusion. I'll have to dial in again with the long PI to see how it really tastes.

Below are photos of the paper after extraction. The first photo is the lower side of the paper still attached to the puck. The second photo is the upper side of the paper next to the puck. It appears that the paper wasn't exactly centered in the basket. How bad do the forensic shots look to you?

Thanks for the help!

Interesting, I can't say anything definitive about the bottomless shot.

Trying to figure out whether the flow coming out is uniform is tricky, basically, you have to consider each hole as a tributary and each downward stream as a river going out to the sea, and you're trying to figure out whether the debit of each river matches the number of tributaries. In your shot it's not trivial to see, but a good sign is that none of the downward stream seem to get clearer/whiter sooner than the other ones, so there's nothing that screams distribution issue or uneven flow.

I would gather that the answers to improving your shot lie more in the direction of a different dial - remember that there are three parameters you can change grind size/shot duration, dose, ratio - rather than improving shot technique (although the latter is always welcome).

Jeff wrote:Are you seeing a ring of darker grinds on the outer edge of the bottom of the puck when you remove the paper? I can't tell from the photo as it is so dark in the image.

Hi Jeff, I lightened the image for better analysis. There is some mottling around 8 o'clock on the puck. You can see a corresponding darkening on the bottom side of the filter paper in the first image of post #6. Do you have any ideas what might cause this?

The photos were taken on my kitchen countertop with a window at the top of the images. The light from the window casts a shadow on the lower edge of puck which might have been what you thought was darkening.