There are many definitions out there on how to make the perfect espresso, but not all are accurate. This definition is based on the Italian way (please also see The 5M's Rule), after all they did invent it!
The word espresso is derived from the Italian word for express since it is made very quickly in comparison with other coffee brewing methods and is served to the customer straight away for immediate consumption.
A single Italian espresso is 30ml (+/- 5ml) of extract that has been prepared from 7g (+/- 0.5g) of fresh ground coffee pressed into a filter holder at about 30 lbs of pressure, through which purified water at 90ºC (+/- 2ºC) has been forced at 9 Bar (+/- 1Bar) of pressure for about 25 seconds.
As you can see, there are many variables and the exact value of each will vary slightly depending on what machine you are using, how you have it set-up and what espresso blend you are using, but the above is a good starting point. As you gain experience with espresso you will find you are able to see when the extraction is correct, the coffee should run out smoothly like "warm honey" which some people say resembles a mouses tail. It should have a deep redish/orange/brown colour that will get slightly lighter towards the end of the extraction, but this crema should make up 10-30% of the final espresso in the cup. If you are checking your espresso in a shot glass you should see it settle like a "mini Guiness"!
Here are the basic guidelines you should remember when setting up your equipment:
•Water Temperature as it hits coffee should be 88-92ºC . Your coffee supplier should be able to tell you the temperature range for your blend.
•Ground Coffee used should be 6.5-7.5g to produce 30ml of Espresso, and it should be firmly pressed into the filter holder (known as tamping) to about 30 lbs of pressure.
•Pump pressure should be 8-9 Bar during extraction. If you have a machine with more than 1 group then set the pump pressure to 8 Bar when all the groups are running as this will put the most load on the pump. With only 1 group running the pressure will be slightly higher, probably around 9 Bar or even 10 Bar if it is a 4 group machine.
•The extraction time to produce this 30ml of espresso should be between 18-30 seconds. The exact time will vary depending on your machine and the espresso blend you use. If the extraction time is too quick you will need to adjust your grinder to grind finer, if the extraction time is too slow you will need to adjust your grinder to grind courser.
•The espresso cup should be warmed before hand. Espresso is only a small drink so if you put it in a cold cup, it will instantly go cold and spoil the drink. More expensive machines have electronically controlled cup heaters with thermostats on top of them to store all your cups, but if you have to use a cold cup heat it first with some hot water from the water outlet.
•In quieter periods when the machines is not used regularly, before making a drink let some steam out of the steam arm and draw some water from the group. This gets rid of any water that has sat there for a while and may now be slightly over temperature.
It is important to recognise that here in the UK some people like to make larger drinks and that to achieve that "real Italian taste" you must proportion your quantities accordingly to the Italian standard. For example if you want your espresso to be 50ml instead of 30ml you will probably need about 10g of coffee intsead of about 7g.
The 5M's RuleThere are many factors that effect the production of an espresso, for perfect extraction they must all be right. In Italy they use the 5 M's rule:
•Miscela (Espresso Blend)
Use a high quality espresso blend , whilst it is still possible to make a bad coffee from good blend you can never make a good coffee from a bad blend! A good blend can contain as many as 14 different origin coffee beans from all over the world. The best blends will contain a high percentage of arabica beans, although this will not neccessarily be 100% arabica. Robusta beans have certain qualities that are desirable in espresso so some of the best espresso blends contain a small percentage of very high quality robusta. This is true for about 98% of Northern Italy's blends.
The grinder must be good quality and the blades must be changed regularly (every 800-1000kg for conical blades, every 400-500kg for flat blades). Blunt blades will burn the coffee as it is ground. The grinder must be set correctly in terms of how fine the coffee is ground and how much ground coffee it delivers to the group handle per shot. You are aiming for an extraction in the region of 18-30 seconds. If the grind is too coarse or too little coffee is used the espresso will be under-extracted and watery. If the grind is too fine or too much coffee is used the espresso will be over-extracted and bitter.
•Macchina Espresso (Coffee Machine)
The coffee machine must be good quality. Look for machines that are Espresso Italiano approved .Their coffee making ability has been approved by the Italian body in charge of promoting quality espresso. The machine must also be set coreectly for your chosen coffee blend, i.e correct water temperature (88-92ºC ) and pump pressure (8-9 Bar).
•Mano dell'operatore (Skill of the Barrista)
It doesnt matter how good your tools are if the operator doesn't know what they are doing! You don't need to be the worlds best barista, but you do need to know a little bit about the espresso process (please also see How to make the Perfect Espresso), so do some research and put in plenty of practice! Regularly check your extraction time is correct, you should be able to see when it is wrong! Ground coffee doesn't keep well, it should be used within an hour so don't grind more than you expect to use in an hour.
Finally, it is important to keep all of your equipment in good working order. Look after it properly with a daily, weekly and monthly cleaning schedule and regular servicing. Always make sure your water filter is changed at the correct interval.