![]() Manual levers do not have limitation, which is why I always advise people who like light beans, but don’t want to buy a technological machine like the Decent, to buy a manual lever machine.Īll the coffee experts I approached preferred light roasts, and most, in a candid moment, would admit to preferring pour-overs to espresso. The ideal pressure curve, producing constant flow with a dark roast, is not the same pressure curve that is ideal for a light roast, or perhaps a coffee bean with different solubility, or those using very-low-fines grinders. This however, is also why I am opposed to spring levers. It’s no coincidence that spring levers create a pressure curve that is almost identical to the green line above: it’s because this pressure curve will create an almost-constant flow rate of espresso, with medium to dark roasted beans. As pressure and flow are directly linked, one can choose to control pressure (instead of flow) to create a desired flow curve. A grinder that produces a lot of fines can cause a pressure “flick” up at the end, but nonetheless, most espresso pucks behave like this. You can see that puck resistance of this espresso gives a peak of 8.6 bar of pressure, which eventually declines to 3.7 bar at the end of the shot. The green line shows the pressure that results from this flow rate. Graph showing a declining pressure profile (green) with a constant flow rate (blue) Here is a chart that shows this in practice. It’s from the Decent Espresso machine software and it’s an “espresso” made with a constant flow rate of 4 ml/s. So, to respect the nature of espresso is to decrease pressure as the espresso is extracted, to work with the reality of puck erosion, and consequently control the rate of flow rate change.Therefore, flow will increase naturally if pressure is kept constant, and too high a flow rate gradient doesn’t taste good.As coffee is extracted, puck resistance will decline due to material loss.Lever machine users had found essentials and crucial truths about coffee: This “manufacturer knows best”, and a goal of removing the need for barista skill, is the trend that eventually gave us the great-step-backwards in drink quality: 9 bar espresso machines. A spring communicates a subtext that “the manufacturer knows best” and once you accept that thinking, further automation (and removal of flexibility) is likely to ensue. With direct levers, the manufacturer intentionally made an open-ended tool. For me, springs were the beginning of the end for levers. This made good espresso easier to attain, as you didn't need to learn how to use your bicep appropriately. The first lever machines used springs, and encoded a “known to work well” lever technique into the hardware. Much experimentation rapidly, oh so rapidly, ensued. So, an open-ended machine was appropriate. ![]() ![]() I believe this is because at that time in history, there were few people who believed in certainties. The manufacturer did not specify the espresso-making recipe in the hardware of the machine: that was up to you. Like the birth of the guitar, where instrument makers wondered “what kind of music will be made with this instrument”, manual levers were an open-ended coffee-making instrument. Put a pressure gauge stolen from a bicycle pump on the group, stick a thermometer in the right place, and voilà, you have made a formidable espresso experimentation device. Your bicep is a far more sophisticated controller than any motor (or spring) could ever be. Looking back in coffee history, I found that the most exciting time was when direct lever machines ruled.
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