RapidCoffee wrote:It's not clear to me whether lungos (which may also be pulled for a shorter time) are subject to over or underextraction. Ditto (but in reverse) for ristrettos.
Well, the point is to pour lungos, normales and ristrettos that are all neither overextracted nor underextracted. Jim is using a version of "Al's Rule," named after Al Critzer from alt.coffee. "....al" lengthened the extraction time for ristrettos and shortened the extraction time for lungos in an effort to normalize brew solids extraction.
....al wrote: As I was trained, the perfect espresso is 30ml in 30sec. That's assuming that all other factors are in line. For longer extractions, the contact time of water to coffee would have to be lessened so that undesirable elements associated with overextraction wouldn't be present in the cup. With shorter extractions, the water to coffee contact time would have to be increased to ensure that underextraction doesn't occur. This is accomplished by grind adjustment.
A good rule of thumb I have developed is this: For every 5ml of espresso above 30ml, subtract 1 sec of extract time. By this formula 1 1/2oz (45ml) would require 27sec extraction, 2oz (60ml) would require 24sec, etc.
The same holds true in reverse. This will find the sweet spot in espresso regardless of volume in the cup (within reasonable limits of .75oz to 2.5oz), as you are optimizing extraction to the desirable elements, maintaining the balance between under- and overextraction. For some reason, grinder adjustment and it's crucial impact on espresso is the most difficult concept to explain and grasp in all the trainings
I do.
As to ristretto. This a different drink altogether. If your grinder is set for regular espresso, and you choose to stop the pour at 25ml, this is simply an underextracted espresso. You haven't hit the sweet spot
yet. The "restricted" part referred to as ristretto is not so much related to volume as it is to water flow through the coffee puck. The ristretto that has been used for cuppings is a 25ml cup in 30-35sec.
This extraction intensifies the organoleptic perceptions of the eyes, nose, taste buds and upper pallate to better isolate the positive attributes of a given blend. Where the positives are accentuated, the negatives are exacerbated as well. The extractions are characterized by a very thin mouse's tail with rich, dark brown crema. Most people don't drink this as their everyday drink, but it is helpful in developing blends. If you customarily drink 25ml (or 50ml doubles), your grinder should be adjusted accordingly.
Unfortunately, Al was speaking in the Dark Ages of Espresso Knowledge, when hapless espresso people specified their pour volume in ml instead of grams. Nowadays, of course, we understand how confusing that is, and baristas who wish to communicate accurately always specify pour volumes in grams.
Also, he didn't specify the dose he was talking about, which presumably was around 7 grams (single espressos).