Volumetric Espresso

This is my first real post, and it’s a rambler! But I had an idea in my head that I wanted to get down, and I hope it gets some people thinking. Thanks for reading.

The new La Marzocco Linea PB has got me thinking. It has a digital display of the flowmeter’s ‘pulses’, and I’ve found the idea of looking at how we could use volumetric dosing of espresso in a different way really exciting. I don’t think this machine hasn’t quite nailed it, and we can go a lot further, but it’s a really interesting start.

I’m not quite sure how the machine shows the pulses, and if you can see a cumulative display, or just real time pulses clicks, but it appears that these pulses aren’t translated into amount of water (although I have read that each pulse is approximately 0.5ml), and you have to choose between either seeing this information, or seeing shot times. Just to be clear, I haven’t yet used this model, so there’s a little bit of guesswork and baseless criticism here, but it’s really about the tangent I went off on, and hopefully it gets others thinking.

So that everyone understands what I’m talking about, when I say volumetric dosing, I’m talking about the little meter inside the machine that measures, quite accurately, how much water has been fed into the shot. This is very different from measuring your espresso by volume, where unstable, foamy, crema makes any comparisons very loose.

Volumetric control of espresso is a little out of favour (although I did enjoy this video). There is no machine that I know of, that gives you responsive, on the fly adjustment of your dosing, and until now, there’s no machine that offers you feedback on that dosing. This means that for anyone who regularly wants to play with their brew ratios, these buttons are just not very practical to use. However, compared to weighing shots, the difference is not one of quality, just ease, feedback and convenience.

I know there’s a lot of baristas who prefer to watch a shot for blonding (or other signs of shot development), rather than weigh or use programmed buttons. This approach seems to be getting a lot less common, at least in my favorite cafes, but there is definite value in paying attention to how your shots develop.

What I’m thinking is watching your shots, paired with a real time read out of the water used, and a shot timer, a barista would have instant feedback on when a shot was off, or their grind needs adjusting to maintain a recipe. We would have the same quality of information as weighing, without fragile, expensive (usually non-waterproof) scales that need to be zeroed for every cup.

We’re going to need a new way of thinking about brew ratios to make this work, where we look at total water used, rather than just what ends up in the drink. This is going to be a big change for espresso, where we will often have more water absorbed by the grounds than coming through into the cup, and we will have some annoying interplay between ground coffee weight (and potentially grind) and beverage weight. People are beginning to get their heads around some of this for filter, where we have separate brew control charts depending on whether we’re measuring total water used or just beverage weight, but this is a lot to take in, and I’m still struggling with it in practice. There is also the issue of the body of knowledge we already have, based around weighing shots, which will not be directly translatable. Even so, I really do think there’s the potential for a really useful tool here, and it’s worth at least exploring.

So, time for a concrete product. I’m thinking a small display, retrofitted to any machine with a flow meter (sorry to all of you with manual paddles), that would accurately display the volume of water used (it could be displayed in grams for those that are more comfortable with this), and would restart a clock every time the water starts flowing. I think this could be done for less than the price of a good pair of scales (though we would need one display per group), and would be a 10-minute job to fit, without changing the machine itself.

I’m tempted to start playing with Arduino kits (as I have been looking for an excuse for a while!) though it may take me some time.

I may have overlooked something major here, but I think this is how I would like to use an espresso machine. I can see an approach and a workflow that would allow manual control while unobtrusively providing information that would be really nice to have. I’m looking forward to hearing others thoughts on this, and if there is anything similar out there.



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