I'll tell you the moral to this story right off the bat. Sometimes a millimeter is the difference between something great and something terrible. Sometimes it pays to look at the details, understand why things work the way they do, and work through a problem logically. Sometimes it's fun to geek out on something, roll your pants into high waters, put in your pocket protector and act like an engineer. It might even save you twenty bucks. Sometimes I wonder if our country's lack of interest in science is partly due to our willingness to unthinkingly replace rather than understand and repair.

I recently bought a new coffee maker at World Market, a Pezzetti italian style moka pot. I did it because I thought the espresso machine I was given last year had kicked the bucket. It turns out that it's working fine again after apparently deciding to go on a short sabbatical for no reason I can determine. I was excited for the new moka pot because I just love the thick, almost syrupy coffee filled with deep caramel flavors that these little pots make. People confuse them with espresso makers but they really excel at the bottom end of coffee taste. Moka coffee usually lacks most of the high, bright, citrus notes in espresso. Both are good but they are very different animals. But I digress...

I filled the new pot with coffee and water and put it on the stove anticipating a stout cup of coffee. It boiled…and boiled…and boiled some more with steam coming out the top tube before it started spitting a tiny bit of extremely thick black coffee out of the collection spout. Then, after a few tablespoons it just quit and started making sputtering, spitting noises and smelling like the worst church-basement-percolated-through-a-two-hour-sermon brew you can imagine. That two tablespoons could have been mistaken for motor oil mixed with paint stripper. In a word it was undrinkable. I tried again a few days later and the result was the same.

I'm wasn't very familiar with these things, but the idea is pretty simple. Build up vapor pressure in the base, which forces the hot water up a siphon tube, through the grounds and into a collection chamber at the top. It's like a cross between a percolator and a pressure cooker. Take a look at this awesome video for a bit of geeky imagery of this in action filmed with neutron imaging. This isn't a complicated machine, so what was the problem?

I couldn't immediately see a problem when I took it apart. The seal and all the filters were fine. I ended up putting it away but I kept thinking, "this is too simple for it not to work when all the parts look right." My mind kept churning on it off-and-on before I realized what had to be happening. If no water was going up the tube then somehow it was losing the vapor pressure in the bottom chamber, since that is the force that sends the water upward. But how was that happening if I couldn't see or feel a leak on the outside?

Top rim is a millimeter or so higher than the filter basket
Then I remembered that steam had been coming out the top for quite awhile before any coffee came out. So, steam was somehow getting out around the filters inside. I went to look at the seal again and happened to notice that the top rim of the bottom half of the pot was slightly higher than the filter that fits inside it and holds the coffee. It was only a millimeter or a bit more, but perhaps that distance was too much for the rubber seal to bridge, letting steam out around the edge of the coffee basket. Hmm…

grinding down the rim on a water cooled lapping wheel
Over the next week I dropped into a couple of stores to take a look at their moka pots. Sure enough, all of them had rims on the bottom chamber that were the exact same height as the filter basket. It was time to experiment. I loaded up the coffee pot with water and grounds, then tightened it as hard as I could to, hopefully, create a better seal. It didn't really work, but I did get about twice as much motor oil/paint stripper solution out of the pot this time around so i figured a better seal must be helping.

Luckily, I had an easy way to fix the problem. I took the pot to my lab and ground the rim down with the sandpaper on a lapping wheel. You could do this easily enough with sandpaper mounted to a board, but a lapping wheel takes less time and the water jet helps keep things cool. You can see from the picture that the rim matches the height of the filter basket now after just a minute or two of grinding.

Rim even with filter basket after grinding
Then came the moment of truth. I loaded the filter basket with freshly ground Indonesia Gajah Aceh from Stumptown, filled the bottom chamber with water, and put it on the stove. This coffee is already just full of deep, intense, earthy flavors…my mouth was watering imagining how rich this coffee would be. I hoped I wasn't going to be disappointed yet again.

It worked! No steam came from the tube in the center of the collection pot, instead a steady stream of coffee issued forth with no sputtering or spitting until the pot was full and the water chamber was empty. The coffee was awesome…and is fueling this late night blogging session as we speak; thick, rich and chock full of bitter chocolate, carmel and straight up dirt.

Sometimes it pays to work through a problem like an engineer, understanding how things work and the principles behind it. I think too often now days we would rather buy something new than fix what we have and that is a shame. My grandfather used to spend lots of time tinkering and fixing things, and creative repair is a daily occurrence for my father the wheat farmer. Watching them taught me that if you understand how something works you can usually fix it or improve it. That is the essence of engineering and science.

Perhaps we Americans have so few kids interested in science because we aren't teaching them how rewarding it is to observe, troubleshoot, and creatively repair things in our lives. You can't learn that skill if you throw things away every time they don't work. Which reminds me…maybe I should figure out why that espresso machine decided to quit turning on for two weeks and then fixed itself for no reason. I'll keep thinking on that one while I try desperately to finish my PhD. Until then, my advice is to avoid moka pots from World Market unless you want to repeat what I just did.
The moment of truth. A perfect brew with no sputtering!