Why no 3 way valve

During the first few years we started making the Decent Espresso Machine, I would often hear criticism that the Decent “lacked” a 3 way valve and thus did not flush properly at the end of espresso.

I patiently repeated my answer that this was not a lack at all, but a decision we made because it seemed to us that using the same tube from the water heater to the group, both for clean water in (to make espresso) and dirty water out (to release pressure) was a bad idea.

All espresso machines (that I know of) before Decent did this “backflush”. We thought that coffee oils would likely build up in that tube, go rancid, and slowly degrade the quality of future coffee.

But our position was alone. Nobody else backed us up or agreed with it.

And people usually didn't believe my explanation, likely because we were the only ones (it seemed) arguing this position. I think people thought I was trying to do “marketing spin” on a “problem with the product” instead of perhaps, maybe having a valid point.

Until I read James Hoffman's “Best of 11 years' writing” book https://decentespresso.com/books where I found out that he'd explicitly called this out as a common source of bad tasting espresso, and thus how important it was to clean this part on conventional espresso machines.

James wrote this 4 years before we even started designing the Decent!  I wish he'd published this book earlier.

Here's the relevant quote from his book:

With the Decent, we release pressure through a separate tube that only ever is used for dirty water. The clean-water-in path holds its its pressure at the end of espresso, forcing water out this path.

Here is a photo of the inside of the group head on a Decent:

The brown tube brings water in (brown=making nice coffee) and the black tube on the right (black=dirty) flushes it away.

We call this approach “forward flush” to oppose it to “backflushing”

It's been a few years since I've heard the “why don't you flush like a normal machine” criticism but I think it's still not commonly known that this common design feature of traditional machines is not great.

This topic came up yesterday, because part of the goal of Weber Workshops new Spring Clean https://weberworkshops.com/products/spring-clean product is to clean this “backflush tube”. Decent owners were asking whether it was worth buying Spring Clean, given that we don't have this same cleaning problem as traditional machines.  I don't know yet, but I'll be getting a Spring Clean myself soon, for testing, and will report back what I find, about the job it does on a Decent.

-john

#cleaning #backflushing #internals

Updated 2021/08/18