Our Thoughts on Spring Lever Machine 2014 Feburary

IMG_4294Matthias Suchert and I have been using a two group spring lever machine made by Bosco Espresso from Naples since we started out in Sep 2011, with the idea of starting from basic in both machinery and bean’s choice in serving two single origin beans as espresso at any time for espresso base drinks.  We read as much as we could on line and has been tasting coffee from modern pump machine and spring lever machine (Prufrock at Leatherlane vs at Present) and pulled shots in tasting beans we know at Londinium Espresso before we made the choice base on the cup to embark on this journey.

With our limited knowledge and experience,  the more we look into the history and construction of vintage spring lever machines and some amazing machine restoration engineers had done and designed, the more we realize how little we know.

Our experience is limited to using machines we can get our hands on and pulling shots from beans that are not too dark in showcasing the origins or particular terrior/ process. So if you have other thoughts and ideas please help us expand our ways in approaching the creation of better coffee. The following are some of the questions we had during the process of choosing machine and also from speaking to customers and visiting baristas to our bar:

Why do we choose spring lever machine over modern machines?

We thought, if we start, we should start from the ground up: Use single origin beans and a machine that could make decent shots of them. If it needs going back to the engineering of the beginning of modern espresso (with crema) then let it.

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Moreover, both of us are, on one hand are rather visual based, there is nothing better if the process is reflected in the working of the machine, on the other we are rather hands-on, we love the physical aspect of literally pulling the lever and get to control the shot during the process of extraction to just pressing a button or a paddle that relays to electronic controls (we frankly have limited budget as well)

What’s the difference of a Spring Lever Machine to most other espresso machine we see in coffee shops?

Spring Lever Machine uses spring to achieve the required pressure while modern machine uses pumps.

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As a result, operation wise, it lacks any push buttons or paddles to produce shots because there is no pump to turn on. One has to pull a lever with force (approx 10kg, in some case more depending on spring) to load a spring to start the process of genuinely pulling espresso.

Spring Lever Machine’s engineering predates any pump driven machines dating back to development from Gaggia’s invention of piston driven espresso machine in 1938.  Instead of a pump, pressure is applied by spring/(s) pushing water down through the coffee bed.

When a barista pulls a shot, this literally means they pull down the lever; it loads a spring by elevating a piston into the cocking position. This allows water to enter the brew chamber to pre-infuse the ground at either boiler or line pressure. When it is released, which is manually controlled, the tensioned spring then pushes the piston down, forcing water through the coffee bed at high pressure which then decreases gradually to zero pressure.

How does the different mean in producing pressure in Spring lever machine differ to modern pump machine reflect in the cup?

Our experience in using modern pump machine is limited, but we can probably look at the steps in pulling a shot and its properties to speculate on the difference:

First, on pulling down the lever and into cocking position, it is the pre-infusion stage: water enters the brew chamber through 4 holes and pressure is at boiler pressure/line pressure, which the barista has full control on length of time. Some machine has an adjustable restrictor in controlling flow rater of water as well. This is different to most pump machine, pre-infusion is preset. (except in Synesso, Strada, Slayer). It is believed pre-infusion enables one to reduce chances of channeling so it is much favored.

Second, on releasing the piston, the pressure reaches as high a static pressure of 12bar or higher in some machine. This forces an even column of water through the coffee bed, where as in a pump machine, water exit from a couple of small holes at the dispersion plate. This even yet gentle column of water enables you to have any headroom in the coffee pluck without affecting extraction, which is something pump machine cannot do.

Third, as the piston is pushing down, the pressure naturally decrease to zero very smoothly due to physicality of the spring. The barista can at any time increase or reduce the pressure by manipulating the lever, which is exactly what some of the most advance machines are trying to imitate electronically through the pump. These machines generally double the cost and one has to deal with electronic components, while most of the other pump machine has either line in preinfusion or full pressure to 9bar only.

Forth, the temperature of water in the group drops very slightly in relation to time where as in pump machine they are often fairly stable. We didn’t find any dramatic issues with this but somehow it has less chance of a bitter cup.

All these attributes of spring lever machine results in a slight different cup to most pump machine: often fuller body more velvety mouth feel and easier drinking cup with single or blends. Somehow with our little experience it wasn’t that difficult to repeat decent cups, which never surprise us.

Despise all these controls and properties, from talking to a lot of barista before we start and also when barista first visited us, it seems in general they don’t like spring lever machine at all and think they are very difficult to use, fluctuates in temperature and don’t produce a clean cup.

I guess most baristas learn to operate an espresso machine by pressing a button to turn on and off, or a paddle. Some works with volumetric control so anything different makes them skeptical, adding on top a max resistant of 10kg pull it may not be so desirable if they have to pull hundreds of shots a day.  Moreover, in the old days, there isn’t automatic refill of water, so the barista has to watch water level, look at the shots (on how it pulls), work on milk, it may just be too much, not to mention if it is gas control.

Furthermore, from previous experience of tasting coffee from spring lever machines, they normally don’t serve very tasty drinks due to location or cultural difference. It was only until Gwilym and Matthias started Prufrock at Presents I was surprised at the difference.

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On the issue of temperature fluctuation and control, there are several design on how spring lever machine are engineered which gives different degree of consistency and ease of control. We had to learn the behavior of our machine(a hybrid dipper) when it is on idle and in use (busy or quiet period) but after that, there seems to be a repeatable pattern that is not too difficult to manage. In a very odd way, we speculate whether the machine is designed to have ‘uniform’ temperature or just a range, so that on brewing, it drops, extracting less towards to end to reduce bitterness.

It is worth looking into how typically spring lever machine are designed to understand the character in temperature control. We looked into several design but they have similar group head design: it is very heavy brass, internally there is a colar, enables a space between the outer wall and inside allowing water to either circulate or sit in.

First, most Spring lever machine are typically dipper system: a very heavy brass group head directly mounted onto the boiler conducting heat to keep exposed group warm. Internally there is a tubing connecting the group to the bottom of the boiler (cooler temperature). So brew water and steam uses the same boiler. Although this keeps the group at higher temperature for group to be ready to use, but after succession of  shots the group might overheat even it is engineered to be a heatsink with heavy brass. So barista typically switch between groups or use a cold towel.

Second type is a hybrid dipper: the group is mounted onto the structural carcass, the large tubing that connects boiler to group has a secondary chamber for brew water before entering group. Although the group is cooler on standby and needs warming up after idle for over 5min, yet the temperature of brew water is very consistent on consequence of shots (93.2-5c, using SCACE2), unless the pressure stat is set very high.

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Third type has group mounted onto structural carcass but water is feed by an open loop thermo syphon: the group has an inlet and outlet. A circuit of water is moving continuously into and out of the group from the boiler directly to keep it up to a constant temperature. Hot water will escape into the brew chamber only when lever is pulled. This system keeps the groups up to a fairly good standby temp without overheating and provides a reasonably stable shot temperature.

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Forth type has groups mounted directly onto boiler to conduct heat and water is heated by heat exchange before entering group. Using heat exchange method to heat brew water separating from the steam boiler is a way to give an extra control of temperature stability (one can control flow inside to optimize temperature)

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The fifth type that we know of is with groups mounted off the boiler, heated by thermosyphon from a heat exchange. . This machine is equipped with the optional adjustable needle-type restrictors, so one can adjust temperature separately per group. Also the optional switch activated automatic temperature purge system is installed. No need to flush the group to get to the optimal temperature after being idle for a while. In theory this provides the best control of standby temperature and also shot temperature as both can be controlled without much effort. (photo from Kees van der Westen)

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All these are engineered base on thermodynamic theory using some heavy duty material, like the group head weights over 5kg to act as heat sink rather than delicate electronic controls. So it lacks the modern numerical display nor PID temperature selection down to one tenth of a degree which one might like to adjust for different roast level or origins. Using spring lever has to rely on manipulating preinfusion time to micro manage temperature.

Is there anything else that makes Spring Lever Machine stands apart to modern pump machines?

The theatrical visual aspect of pulling a shot that is actually coherent to the design of the machine: From pulling down the lever, lifting it then seeing levers rising up as the shot brew, I don’t know how pressing a button or pushing paddles can replace that. It is particular dramatic when there is multiple groups with levers moving up and down.

The physical tactility on the pulling the lever somehow makes one connects a little more to the working of the machine. I guess from the customer point of view, it is also a performance aspect of the barista.070

Furthermore, if a barista wants the customer to focus on the senses particularly visual and taste, the sound of pump humming in the background may not be so desirable. The silent spring is really a bless.

Coming back to cleaning, because there is no back flow of water, the shower screen and brass block of the piston is much cleaner, cuts hours of the after hours cleaning daily.

Of course, there are issues one needs to be careful. The levers can break jaws if there is no resistance in the portafilter and contrary if too much coffee clogging basket, one cannot just unlock the portafilter, otherwise the pressure of hot water could make some damage.

Would you recommend coffee shop owners to consider spring levers?

If one looks for simple elegant solution in offering quality drinks then definitely, it makes espresso an enjoyable experience, not to mention it is an amazing conversational point. However, if it is about numbers then maybe not, particularly it will put a lot of not so keen barista off with reasons mentioned.

You can see spring lever use in some world renowned coffee shops, such as Blue Bottle Coffee, for their single origin. Prufrock at Present always wins preference than their Leatherlane shop!

On the development of modern machines goes, we respect very much the effort being put into perfecting the condition in pulling espresso such as utilizing the pump to reduce physical constrain, precision PID temp control for consistency in both quiet and busy hours; refine temperature control down to 0.1c  for different roast levels and origin of beans; programmable volumetric/ weight controls, pressure profiling, etc are very obvious. While some of these spring lever machine lacks but quite a few of the sort after characters and quality were inspired by Spring Lever Machine.

I guess it is like what the head engineer at Simoneli has said, spring lever is like driving a Ducatti, where as the modern machines are Honda. One cannot replace another but it is good to have the opportunity to clarify any misunderstanding. A roaster friend was really dubious on spring lever machine, after he had a cup from us and pull quite a few shots, he got his roastery one and simply enjoyed the process and more importantly, the cup.

How about for home barista?

If one consider buying an espresso machine as a long term investment and also include the long term cost of beans use in dialing in on pump machines, spring lever machines often come as a revelation from lots of users. Look up voices in forums as evidence, but make sure you get a proper one with commercial group head.

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7 thoughts on “Our Thoughts on Spring Lever Machine 2014 Feburary

  1. fatnancy says:

    would you recommend investing in a SCACE device? how useful is it in callibrating a lever machine?

    • Some kind barista brought it over to test the machine for understanding pressure and temperature stability. If it is seen as a standard instrument then I guess we can’t argue the usage. For temperature it worked well with the electronic monitor (not include in the kit) However, because it uses a standard restrictor so you do not know the actual applied static pressure the spring’s output.

  2. fatnancy says:

    so, the pressure stat doesnt work on spring lever?
    I guess, on a spring lever, a SCACE becomes a $500 thermometer?

    • Matthias says:

      It depends what you want to “calibrate” – if it is pressure, you can’t really do much but either applying extra hand pressure to the lever, removing pressure by slowing the lever’s ascent or changing the springs. If you want to “calibrate” the temperature, you need to know that it does fluctuate with use with some models without Thermosiphon, as it did with our machine. Over time your hand will be good enough to tell you when to swap groups. You can change the pstat setting for achieving lower/higher initial temperature, if so desired.

      PS: One can calculate the actual applied static pressure with basic physics: http://www.reliablespring.co.uk/calculator.htm

      It requires you to know the spring’s fundamental characteristics, some which the manufacturer of your coffee machine may divulge. At the end of the day,even if you cannot answer it satisfactorily, it will still make a great cup of coffee.

    • I guess it is relevant in a certain way as this is a standard in the industry for machine testing. The restrictor is calibrated to a certain size ( I assume) to tune a pump’s applied pressure. Temperature probe is attune in simulating actually coffee making. The only thing it can’t measure is what is static pressure/ force from spring. Some other brand makes one with a tap so you can turn on and off but they say theirs is less accurate

  3. fatnancy says:

    ive just found someone who will lend me a SCACE, so im gonna play with it next week. i have my bosco set at 1.1 bar but feel that i could do with fine tuning it. im interested to know what happens in the pre infusion too. cheers!

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