Seasoning a coffee machine

September 26th, 2009

By seasoning a coffee machine – I am talking about pulling a few shots per group having done a chemical clean. Conventional wisdom says that if this is not done then the coffee will have an unpleasant metallic tang to it, because the machine is “too clean”.

Something about this just doesn’t sit right for me. I am going to assume that if you are reading this then you probably clean a coffee machine the same way that I do: portafilters regularly scrubbed and immaculate, screens dropped and scrubbed clean, dispersion screw kept clean, group seal cleaned and dispersion block scrubbed clean. After all this we do run the backflush routine with a small amount of chemical.

For years I did the backflush bit wrong.  1  These days I find the routine on the side of a bottle of Full Circle the best explanation and method.  2

Now as I understand it we are really trying to clean a small section of tube that runs between the solenoid valve and the dispersion screw.  3  This tube gets dirty because coffee travels up it during the pressure release at the end of pulling a shot when the solenoid opens up.  As such this tube can get a build up of unpleasant flavours.  This happens very slowly – compared to how quickly the dirt in a portafilter builds up and ruins a shot.  Flushing in between shots probably helps slow down the build up in the tube.

backflush

So when we backflush we switch the group on two pump in water to dissolve some chemical and then switch the group off, the solenoid pressure release sucking the chemical up the tube where it can start to strip off any build up.  We repeat this process to ensure thorough cleaning and then we go through a rinsing process.

I think we all agree that at this stage there is no chemical left behind, and if there were it would be a specific and unpleasant taint to the next shots.  However we are told that the next shot will taste bad regardless.  I would like to suggest that this bad taste is primarily due to a loss of heat at the group, affecting the brew temperature and creating an unpleasant underextraction.

First of all – this piece of information is pretty much written in stone but how many of you have tasted the next shot out?  Exactly how did it taste bad?  Very few people have tasted it because they are always told it is going to be bad, so why would you?.  Those of us that have have probably done so in one of two scenarios:

1).  Tasting immediately after a backflush.  Here the group has likely cooled down, because very little water has moved from the boiler out of the front of the group.  On some machines this may influence the brew temperature.   Plus we’ve left our portafilters out for a while and I would contend that the first shot you brew will be under temp.  We may have gotten into the habit of using that shot to bring the group and portafilters up to temperature, because we know it is a wasted shot regardless.  4

2).  The next morning.  Here the group has again cooled down due to a long period without water travelling from the boiler to the dispersion screen, and the shot would likely be undertemp.  If you leave a stock Linea alone for 30 minutes during the day you need to flush a lot of water through it to get it back up to maximum, stable brew temp.  What if you left it 8 hours?

In both cases it is somewhat likely that the poor taste of the shots could be primarily attributed to brew temperature.  I asked Josh Dick from Urnex this very question during our Barista Magazine article and there didn’t seem a more likely explanation.

I have a Synesso Hydra.  From leaving the pump to hitting the coffee the water travels through a good deal of metal piping.  Are we seriously suggesting that while it will pick up no metallic taint from the majority of its journey, but if a small tube near the coffee is not coated in coffee oil that it will somehow have a massive impact on taste when the rest of the machine’s metallic surface will not?  If that tube is dirty then I absolutely believe that it will have a negative impact on the shot, but too clean?

Last night I did a very simple experiment.  I chemically cleaned my machine, and left chemical in it for well over 2 hours.  I want it as clean as was possible.  This morning I dialled in the grinder on the left group, and once happy I then flushed the right hand group up as hot as I could.  Once I was satisfied that it was hot enough I pulled a shot and I drank it.  The seasoning shot.  Did it taste bad? No. Did it taste sour or metallic?  No. Could the fact that it was my first coffee of the day have influenced me? Absolutely.

However – lots of you reading this have coffee machines.  Lots of you probably have Scace devices.  I am absolutely happy to be proven wrong but I would just like to get to the bottom of this phenomenon.  How do seasoning shots taste to everybody?  Do we all agree on what is wrong?

  1. I would put chemical in, switch on the pump – assume that this part was the cleaning part and let is run for 30 seconds and then just rinse everything clean.  A complete waste of time.  ↩︎
  2. By the way – given the choice between Cafiza and Full Circle is anyone not opting for the sustainable option?  It may cost a little more but surely the tiny cost increase per backflush really doesn’t matter.  ↩︎
  3. If I am wrong here – I am more than happy to be corrected!  ↩︎
  4. I accept that on some machines backflushing and then immediate brewing may result in high/higher brew temperatures, but rarely are people pulling shots immediately afterwards – usually there is sufficient time for that extra heat to dissipate.  ↩︎

Comment Policy

There are no longer comments on new posts. If you'd like to respond you can find me on twitter.