baldheadracing wrote:I am reminded of a quote:

-John Steinbeck, East of Eden

Used as-is, spring lever machines typically:
- start with an upwards draw of air through the puck;
- followed by a variable time of pre-infusion at very high temperature, very high flow, low pressure, and variable volume; and then a
- quick rise to peak pressure, followed by a linearly-declining pressure; combined with a
- linearly-declining puck temperature during the pull.

I see three classes of spring lever machines for light roasts:
First: Machines with spring lever groups that were designed for a low-grown Brazil-dominated coffee landscape where everything was roasted to at least to the beginning of second crack;
Second: Machine(s) that by happenstance are great at light roasts; and
Third: A "pump machine with a lever group bolted on" (Reiss Gunson quote).

The first class of machines can only get hot enough for light roasts by increasing boiler pressure. This upsets the thermal equilibrium of such machines. Thermal equilibrium meaning walk-up-and-pull anytime and keep pulling shot after shot (given a reasonable minimum rebound time) and always getting the same brew temperature profile. Most(all?) vintage one-group machines designed for commercial use are like this. You can make these machines hotter and they'll work, but I think that they might not make a light roast shine as much as the next two classes of machines.

The second class of machines has groups that over-heat - the brew temperature climbs after consecutive pulls/longer warm-up times. Coincidentally, this leads to not having a declining temperature profile during a pull. These are usually small groups - the Elektra Micro Casa a Leva is the most well-known example, enabling tea-like long brew ratios with amazing clarity and separation of flavours when pulling nose-bleed-light roasts. However, allonges are not happening at 17g doses, or even half that - my typical long pull is 6.5g-7g in, 30-ish second pre-infusion, to get around a 1:6 brew ratio.

The third class are fast pigs - Strega, Londiniums with pumps, LM Leva X, ACS Leva's(?). A pump lets the group be pre-infused at various pressures and/or be filled with more water during pre-infusion. While directly controlling available water volume, this also controls extraction pressure profile (due to differing compression of the spring at different engagement/catch-points) and also the temperature profile behaviour during the shot. As these machines have significant technological differences, exact behaviour will vary. (As an aside, I think that a Strega pulling these kinds of roasts strongly benefits from a pre-infusion pressure gauge. Also, an additional switch on the pump is convenient. A PID on the grouphead heaters is probably also a good idea, but I use flushes instead to (only) lower brew temperatures.)

Finally, I'm not sure if you would classify this as a "fancy ... ritual," but in all three types, manual retardation of the spring can be used to lower extraction pressure, as adeptly demonstrated in another_jim's famous video review of the Strega where he pulls a light-roast Geisha (video , go to 3:50-7:55). This takes some practice to do, and, at least in my experience, is nowhere near as easy as it appears in the video .

Just my opinion; I'm sure others will disagree. FWIW, my guess is that the Leva X would be the best spring lever machine for light roasts.