It seems like a lot of the higher end espresso machines come with a 58mm portafilter. Does this larger diameter have some improved effect on the resulting espresso?
MT San talks about portafilters and the resulting differences between these portafilters that are different in size.
I will discuss the differences in espresso extraction as a result of portafilter and subsequent basket size.
Assuming that the only variable here is basket diameter:
Scientifically, pressure applied is normally measured as force per unit surface area. Taking the bed of coffee as a flat surface, and we assume traditional extraction pressure of 8 bar, the net extraction force upon the coffee puck will be greater for larger surfaces.
8 bar = 800kPa = 800 kN/m2
Now given two different basket sizes 58mm and 52mm which are 0.058m and 0.052m respectively, the net force on the surface of bed of coffee will be:
Surface area: πr2 = π*0.0292 = 0.00264207942
Net force on area: pressure x area = 800*0.00264 = 2.11 kN
Surface area: πr2 = π*0.0262 = 0.00212371663
Net force on area: pressure x area = 800*0.00212 = 1.7 kN
We can see that the larger portafilter is subject to a higher force of extraction with the same pressure. What this amounts to in practice is very much dependent on your setup. However it should tend towards better consistency in extraction. This is because, for a given dose, more of the coffee is in contact with the water at the bed surface and so has a more direct pressure gradient through the puck as it will be comparatively thin in the larger basket helping to reduce probability of channeling.
However, observable effects in practice will be slight to none as many other variables will take precedence in affecting shot flavour and the difference in extraction force will be accounted for silently in your dial-in process.
Short answer, yes. There are a few differences. Does this differences affect the home brewer? It depends. Let me explain the differences in between the three main types of portafilters:
- pressurized: This type is mostly smaller in diameter (52 mm) and made partly from plastic material. As the diameter is smaller, keeping the pressure is easier even if the tamping is not even, grounds are not homogeneous in size. Thus, this is why this is the most common portafilter for entry-level home machines. It hides the irregularities. An example photo from Wikipedia is below.
- regular: This type is mostly made from pure metal and larger in diameter (58 mm). Thus, their heat retention is greater. This makes temperature equally distributed. This type is more sensible to tamping errors or grinding irregularities. But, this may be a good thing actually if you are looking for the perfect cup. Here is a photo I copied from La Marzocco website.
- naked: This type does not have the bottom spouts. This is very good if you want to see what's going on inside the portafilter. E.g. if you have problems in tamping, you can see if one side is flooding rapidly than the other side. Very good for education. Also, very nice for photographers. One nice photo including tiger stripes from wikipedia, again.