Definition of Espresso
The definition of an espresso is a much debated subject, as people's ideas of espresso vary according to their own taste perceptions. Almost every aspect of espresso making is up for discussion: from espresso blend to tamping technique to volume of the espresso. But then, espresso is an art and a barista is a skilled craftsman. This is why events such as the World Barista Championship are becoming increasingly popular, as each contestant is producing something original.
Even the origin of the word espresso is split into two camps; those who believe espresso simply means 'express' or 'fast'; or those that believe it comes from the Italian verb 'espressimante' which translates as 'especially prepared for you' (made to order).
Nevertheless, there has been much scientific research into making the perfect espresso, or 'God Shot', and a set of parameters have been defined as to what an espresso should be:
- An espresso is made with between 6-8 grams of ground coffee
- The temperature of the water when first in contact with the espresso is between 90-95°C
- The pressure of the water on entry is between 7-9 bar
- The volume of an espresso is between 1-1.25oz (28-36ml)
- The time it takes to brew the espresso is between 25-30 seconds
While meeting all these requirements alone will not make the perfect shot, they do serve as important guidelines, especially for beginners. Though there is considerable variance in each of these parameters, you should find the level within each parameter that works for you, your machine and your coffee, and aim to be consistent to that level.
An espresso is made with between 6-8 grams of ground coffee (or 12-16 grams for a double shot). The actual amount of ground coffee you use to make an espresso is dependent on the espresso machine. This is because, during the brewing process, the puck of coffee will expand and so it is necessary for there to be a gap between the puck and the dispersion screen of the grouphead. If there is no gap then the puck will not infuse evenly, as water will struggle to penetrate the coffee all the way to the perimeter of the portafilter.
To test if you are using too much coffee: dose and tamp the portafilter as usual and attach to the grouphead (but do not turn on the espresso function). Now remove the portafilter and check to see if any coffee has been left on the dispersion screen or an impression made on the puck. If either of these are the case, reduce the amount of coffee dosed and try again.
Once you have found the correct dosage for your espresso machine, do not alter it. If you can dose consistently then you reduce the amount of variables that can go wrong when making espresso.
Temperature and Pressure
Both temperature and pressure affect the level of extraction from the coffee puck. Too low, and the espresso will be under-extracted; and too high, it will be over-extracted. Unfortunately, boiler temperature and pump pressure can only be adjusted on some high-end domestic espresso machines. However, there are things we can do to tweak the temperature on all espresso machines.
The process of tweaking the temperature of an espresso machine is known as 'temperature surfing'. The basic technique is to draw cold water from the reservoir into the boiler until the boiler's heater kicks in. To do this, simply turn on the espresso function and run water out the grouphead until the thermostat light comes on. When this light goes off again the boiler is now at the highest temperature in its range (usually around 95C). You can then choose either to brew your espresso immediately or wait a set amount of time to allow the boiler to cool slightly.
It should take between 25-30 seconds to brew your espresso, as this is the optimum level of time to gain the fullest extraction before releasing bitter compounds and excessive caffeine into your drink. Your espresso should have reached between 1-1.25oz (or 2-2.5oz for a double) in this time. It is the coffee grinder's role to control the flow rate. If your espresso reaches this volume too quickly then adjust the grinder to a finer setting, and if it takes longer adjust the grinder to a coarser setting. Do not be tempted to change the dosage of coffee or tamping technique as these should always remain consistent.
The 25-30 second optimum brew time applies to all espresso drinks; it is only the volume that alters. So in this space of time, a Ristretto (meaning restricted) should be 1oz or less in volume and a Lungo (meaning long) should be approximately 1.5oz. Therefore, to make a Ristretto, alter the grinder to a finer setting than that you would use for normal espresso and for a Lungo a coarser setting.