In an effort to help espresso newbies (hey, there's nothing wrong with being an espresso newbie!) get better shots and more crema, my fellow alt.coffee regulars and I had various discussions on the ways and means to improve.
The result from my end was to come up with The Crema Rule, which, if followed, should ensure good shots with lots of crema. It is as follows:
The following instances:
- Fresh Beans plus
- Adequate machine plus
- Adequate tamp plus
- Adequate grind plus
- Fresh water
Will all equal a 25 second pour (from the time you activate the pump switch) for 2.5 oz (±0.5 oz) total volume for a double shot, which in turn virtually guarantees good, rich and full crema, not to mention a rich, thick shot.
Beans roasted 12-24 hours before you grind them are the freshest possible beans you could have, and definitely fresher than almost any storebought bean you could get. Most beans need to "degas" a bit after roasting, so 12 hours is a good wait time. Beans begin to oxidize almost immediately which in turn damages them. This means that beans capable of producing great crema a day after they were roasted might produce no crema at all 7 days after they were roasted (and kept in less any environment that contains oxygen, including your sealed tight jars). Fresh beans are key - and keep them whole until just before you want to brew. Don't pregrind - grind only seconds before you pull your espresso shot.
This means you have a pump driven machine (or a piston lever or spring lever machine) capable of heating water to desired brew temperatures (approx 192F-200F, or 90 to 96C at sea level). Further, the machine must be capable of delivering the water at least 9BAR (about 130PSI) of pressure in a consistent, sustained manner. It must also be able to maintain the brewing temperature during the shot. The machine should be well maintained and clean, especially around the brewhead and portafilter. There are many machines on the market capable of these parameters, priced as low as $50 for a refurbished model, or as high as $2000 or more.
While some people claim tamping your espresso ground coffee isn't necessary - let the dispersion screen (that screen in your brewhead of your machine) do the tamping - I say this is false and bad advice. So do most modern day espresso experts - tamping is a variable you must control on your own to get consistently great shots. Don't give up the variable. One noted expert, David Schomer, recommends a 30 pound tamp. The book Espresso Chemistry, by Andrea Illy, also recommends a suitable (and heavy) tamping for proper brewing controls.
How do you know what 30 pounds of pressure is? Take your tamper and portafilter to the bathroom, and tamp on the scale - see what 30 lbs of pressure is like. Why tamp at 30 pounds? 20lbs or less allows too much water to find a "path of least resistance" around your grinds, instead of fully saturating it. The result is less extraction from your grounds. More than 30 pounds shouldn't be necessary, unless you're compromising for a coarse grind (see below). Note, Schomer's commentary is based on commercial grade machines, but is a good rule for home machines as well.
This goes hand in hand with your tamp. You should grind to a fineness that, tied in with a 30 lb tamping pressure, delivers you a 25 second shot. If your shots are too short in time for 2.5 oz in a double, grind finer. If your shots are too long in time, grind coarser. If you aren't capable of grinding fine enough, you need a newer, probably more expensive grinder, preferably a conical grinder like the Solis Maestro, a flat burr model like the Saeco M2002 models, semi-pro flat burr models like the Rancilio Rocky or Innova grinders, or my personal choice these days - the Mazzer Mini (expensive though - $399 to $600 depending on where you buy).
This one is a given, and quite obvious. Use fresh filtered water. Espresso is 97-98% water after all. Why use something less than perfect?