Rabbit warren time...
Long time newsletter subscribers will know that occasionally (perhaps frequently) things get geeky here. This is particularly geeky...
I've been using products from a company called Sworksdesign for a while. They produce an amazing step down billet basket which changes the aspect ratio of the basket producing more elegant extractions. They also packed something called a "dynamic shower screen assist spring" with my last order. I have written about this before. However I discovered an amazing property of this assist spring as I watched the extraction flow rate on our Bookoo coffee scale.
As your machine is extracting espresso, a pump is filling (and eventually pressurising) the space holding coffee grounds and air in the portafilter. As water saturates the puck, the puck expands both with water and gas bubbles (mostly carbon dioxide). Puck expansion results in a relatively uniform flow rate throughout the course of the extraction process using a pump espresso machine.
Spring lever machines produce an entirely different flow rate. I have written about this phenomenon before as well. The physical characteristics of the spring which drives the lever in these machines results in a reduction in extraction pressure as the extraction progresses. You can think of this as a reduction in forward pressure causing this result.
The dynamic shower screen assist spring produces the same flow profile but as a result of an entirely different mechanism! The process here is to place a puck screen on top of your fully prepped coffee bed within your portafilter and then place the assist spring on top of the puck screen before securing your portafilter in the group head. The assist spring compresses the puck as it is saturated and effectively increases back pressure meaning that as the extraction progresses the flow rate slows... a similar extraction profile to a spring lever espresso machine but using a pump machine. You can see the flow rate depicted in the graph at the top of this blog post.
I love the extractions this piece of equipment produces, and my crazy desire to spend a large amount of money on a lever espresso machine has diminished. I love this so much that I'm toying with the idea of winding my own springs for use with 58 mm portafilter baskets (the only springs that Sworksdesign produces are designed for the step down billet basket).
I'll keep you in the loop!
P.S. The Limited Edition Honey Hydro process Ethiopian Yirgacheffe has sold out. Link here to the second Limited Edition Brazil Vinhal Farm Natural 2x Fermented.
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