qualin Senior Member Joined: 30 Jun 2012 Posts: 681 Location: Calgary, AB Expertise: I love coffee
Espresso: Izzo Alex Duetto 3 Grinder: Mazzer Mini Elect. Type A Vac Pot: Looking to buy Drip: Manual Roaster: Considering?
Posted Sat Nov 2, 2013, 11:31pm Subject: Re: 58mm
La Spaziale designs their machines with a 53mm portafilter because they believe that a smaller surface puck area with a deeper puck results reduces the possibility of chanelling.
Personally, I have honestly have no idea how 58mm became the standard. It doesn't even tie to any non-metric standard. I mean, it would better sense to use 2 1/4 inches or 60mm instead of this oddball number. Maybe someone can enlighten us?
All I know is that since the majority of accessories out there are 58mm, such as portafilter handles, baskets, etc, it makes sense to stick with one standard. Even if it is oddball.
Garbage In, Garbage Out, for every step of the process. From Beans to grinder, grounds to machine, coffee to cup.
The shape of the coffee cake, determined by the filter's shape, is important when considering peculiar forms that deviate from the traditional ones, universally accepted by current coffee machines. The classical shape of the double dose is cylindrical, around 12mm in height by 60 mm in width, the exact dimensions depending on the machine. If this height-to-diameter ratio of about 0.2 is lowered, very fine grounds are required for coffee to percolate within a standard time; this choice would degrade the reproducibility of percolation, because of the creation of localized channels by water. A larger height-to-diameter ratio would give the cake the shape of a column; in this case, optimal extraction would demand an excessively high pressure (as in liquid-phase chromatographic columns). Conversely, for normal pressure values the grind would be so coarse as not to offer a sufficient number of fractured cells, resulting in a low extraction. Consequently, only minor variations from the optimal form of the established filter can be recommended.
Using Petracco's recommendation of a H:D ratio of 0.2, it's easy enough to determine that the volume of 58mm puck is 122.6cc, and a 53mm puck is 93.5cc. The 53mm Spaz double basket should therefore be dosed with 76.3% of a 58mm dose, and a 14g dose in a 53mm basket is roughly equivalent to an 18g dose in a 58mm basket. If you keep the puck height constant, instead of using Petracco's H:D ratio, then the equivalent 53mm dose is 15g (83.5% of 18g).
DavecUK Senior Member Joined: 21 Sep 2005 Posts: 1,469 Location: UK Expertise: I love coffee
Posted Mon Nov 4, 2013, 2:52am Subject: Re: 58mm
I prefer less depth in the puck and hence baskets of 58 mm. I'm not sure how much real science there was in it, or was it just serendipity that settled on the 58mm size. The OCD type engineer would have probably developed a 60mm basket.
There are a number of factors at play.
Having a puck deep enough to be able to offer enough resistance for a correct extraction and a grind that is not excessively fine
Avoiding a puck that's so deep grinding must be excessively coarse
Pucks that don't channel
Holding from 16-23g coffee for a double.
In my opinion, it would be desirable to get the thinnest puck (hence largest diameter portafilter) possible that meets the above criteria (with the caviats below). I have done various experiments (as far as possible at home) and prefer the taste of the correct type of single basket vs the double basket for the same coffee. I have even tried down dosing doubles to see how the taste changes....difficult because of having to make the grind finer. If I explain my thinking...The issue for me is an "extraction" vs "over extraction" one, it's something we always talk about and we all know the taste of, especially if you have had a cafe crema, or split the shot into portions. So a little basic (and approximate maths). A standard 58mm double basket presents a surface area of around 26 cm sq, and a depth of approx1.5cm. So a thought experiment for you:
(a) Imagine this coffee held in a square column 38 cm high and 1cm across, you would be passing 60ml of water through to form a double shot. The coffee would have to be ground quite coarse which would limit extraction, but for a moment lets have a "suspension of disbelief" regarding grind levels keeping them similar and perform this thought experiment. Every 1cc of coffee will get 60 cc of water passing through it. I would imagine everything including the stuff we don't want, is going to get leeched out of the coffee (in a similar way to the percolators of old)..
(b) We now have a portafilter 70 mm wide, which has a surface are of approx 39 cm sq, this time every 1cc cube of coffee gets 1.5cc of water passing through it. The extraction profile is quite different.
Now I'm not saying that the ratio of 1.5 -1 ratio of (b) or the 60-1 ratio of (a), of water passing through coffee is correct. The grind sizes will vary massively, as will the pressures required etc.. Of course once we start to get to sizes closer to what we're used to and ranges from say 40mm to 70mm then the grind levels, pressures etc.. become more similar. However the point I'm making is the same. So if we call this thing the WPTC ratio (water passing thru coffee), for want of a better name. Our ideal would be:
The lowest WPTC ratio that meets the 4 criteria mentioned earlier....AND meets the taste test (because as you lower WPTC ratio it's going to taste better and better up to a point, then it's going to start tasting worse as you continue, a sort of bell shaped curve)
+1. I've never been a fan of triples. The 53mm Spaz double basket has the geometry of a triple (it's taller than 58mm doubles), and will easily hold more than 16g. But I keep my doses in the 14-16g range because I prefer the taste.
I don't know why 58mm became the established commercial standard, but it may have something to do with engineering considerations. Pressure is force per unit area, and thus larger baskets require more pumping force to achieve 9 bars of pressure. For example, it requires 40% more force to generate 9 bars in a 58mm basket than a 49mm basket.* That's why home lever machines have smaller basket diameters: you can get away with a shorter lever (and weaker springs, in spring lever machines) to generate sufficient pressure.
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