Experienced baristas know all about purging the grinder, but our Technical Services Engineer, Graeme, takes it to a whole new level with his recent experiment looking at the difference between purging a grinder with an auger versus one without. Graeme worked in Curtin University’s Physics department for many years before joining Five Senses, where he combines his passion for coffee and his scientific know-how.
The grinder purge quantity (GPQ) on a Robur manual grinder with no auger is ~15 gram. On a Robur E with an auger it is ~30 gram. Robur E+ grinders have augers.
What am I talking about (stuff you probably already know)?
When you make an adjustment to a grinder there is a quantity of grinds still in the chute and grind chamber at the old setting. You need to purge these grinds or you won’t see the effect of your adjustment. After making an adjustment, we typically grind about a double shot and throw it away. That is probably okay on grinders without augers, but on a grinder with an auger you need to purge two shots. Furthermore, if you have watched the grinds emerging from the mesh in front of the chute (E grinders) you may have noticed the grinds at the bottom come out faster than the top. This will also cause an increase in the GPQ.
What’s an auger?
An auger is the very coarse screw type object sitting on top of the grinder burrs and this makes the grinder faster by improving the feed of beans to the burrs and maybe by breaking the beans up a bit too. Recently I measured the difference on a Kony E with and without an auger and the grind time for 18g increased from ~5 seconds to ~9 seconds. The rotational speed of the grinder burrs is the same, but it grinds faster with the aid of an auger; therefore there will be more grinds in the burr chamber.
Author: Graeme Burton, Five Senses Coffee