peacecup wrote:I don't understand the brew ratio system very well. I can read the numbers, but I don't understand how your 30 ml shot can end up with a 50% brew ratio? Going by volume, AndyS chart claims it should be somewhere over 60%, i.e. a double ristretto. Does this mean you are under-extracting, and getting less solids, thereby resulting in a lower total weight?
I've always used Illy's 7g to 30 ml (1 oz) as a guide to a typical solo, and 14g:60 ml as a typical doppio. This fits right into the volume part of the table, but I have never weighed my shots to check the brew ratio.
Something just doesn't make sense here...
Water weighs 1g/ml, and espresso is mostly water. But crema changes things. I'm generally pulling shots on my Vetrano that run slightly under 2oz (about 50ml) and pour as 100% crema. Some of the crema subsides by the time the shot is finished, but it's still 80-90% crema (e.g., see pix on page 1 of this thread). The shot volume may be reduced by half (to about 30ml) when the crema has completely subsided, especially when using a bottomless portafilter. Its weight, however, will change very little with release of CO2 in the crema.
As many have noted, lever shots tend to have significantly less crema. If you pull a 30-35ml lever shot that reduces in volume to 25-30ml after the crema subsides, it will weigh close to 30g - similar to that 50ml bottomless pour from a pump machine.
So unless you're willing to let the crema subside (and sacrifice the pour

), the weight of the shot is a more reliable measure than its volume. That's why I've been a fan of AndyS's
brew ratios from the beginning. Another reason: weight measurements with a decent scale are much more precise than volume measurements in a shot glass.
BTW, the Italian Espresso National Institute (Istituto Nazionale Espresso Italiano) claims 25ml volume for a 7g single dose. Of course, they also claim 9 bars pressure...