I think I intimated last week that I wasn’t that keen on coffee machines… using words to the effect of "Now you may have determined that espresso machines are not my favourite piece of kit”. Of course you won’t be surprised that I’m actually very enthusiastic about coffee machines!
Now an admission (of guilt?). I’m a teeny bit obsessed with spring lever coffee machines. Many, many newsletters ago I suggested that coffee machines were glorified contraptions designed to heat water and then push that water through a puck of ground coffee. There are a lot of different ways to build the pressure that will push that water: the human body (manual lever machines), pumps (vibration, rotary and gear), and mechanical springs (the spring lever coffee machine). Spring levers are fascinating because they are (mostly) silent (many spring levers do require a small pump to fill the brew boiler), beautiful, historic, and… most importantly… produce a wonderful pressure profile for extracting coffee.
And it’s time for some physics. Anyone remember Hooke’s Law? This law states that the force needed to extend or compress a spring by some distance is proportional to that distance. The way that a spring lever works is that the user has to set the large mechanical spring by depressing a long lever (you’ll see in the photos below). Once the spring is released then the amount of pressure that the spring applies to the water moving through to the coffee is directly proportional to the amount that the spring has been stretched. As the extraction progresses the spring becomes less stretched and the force that it applies to the water falls. So the spring lever provides a profile where the pressure applied to the coffee puck is continually declining.
The benefit (apparently) is that the pressure is lowest at the end of the extraction which is when it is believed the bitterest coffee compounds are extracted - the expectation of flavour profile from a spring lever is one where bitterness is minimised. Sounds great right? You can see why I’m a little obsessed with these machines… and I have never owned one! I should issue a warning here. If anyone is considering a lever machine they can actually be dangerous! If one depresses the lever without resistance the lever can snap back violently. People have lost front teeth!!! Warning complete… back to the narrative.
There are three main lever mechanisms on the market: Bosco, Izzo, and Kees van der Westen. Bosco and KvdW both use 58 mm portafilters whilst the Izzo uses 54 mm.
The Bosco Sorrento:
The Izzo Alex Leva:
And the Kees van der Westen Mirage Idrocompresso:
I’m also going to throw in an image of an antique machine which is probably my favourite lever of all time, the Faema Lambro from the early 1960s: