It seems that everyone's close, but pretty much all around it. 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 11/2oz (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. Damn, I did it again....al