The Guide to the Perfect Espresso
Step 1 - Consistent ratio and weighing
Use a ratio of 1:2 dry dose vs. wet dose (i.e 18 grams in should give you 36 grams in liquid output). Make sure you always weigh your shots to ensure consistent quality.
Step 2 - Use a distributor
A distributor will help even out your porta filter surface to prevent channeling which results in a bitter aftertaste.
Step 3 - Tamp evenly with a 20-30 lbs of pressure
Tamping brings the coffee grounds together to ensure even extraction.
Step 4 - Purge your grouphead before pulling your shot
Water residing in the grouphead is often higher in temperature and may cause your espresso beans to burn so purging the grouphead right before you lock in the shot is a good habit to get into.
Step 5 - Time your extraction
For an 18-36 gram shot, you should aim for an extraction time of 25-30 seconds. If longer than 30 seconds, it means your grind size is probably too fine and you should therefore make your grind size coarser and vice versa.