One of my goals in this blog is to de-bunk a few myths about coffee in general, and espresso in particular.
So we can keep this blog entry focused, let's assume you already have a suitable grinder & machine & coffee.
Firstly, unless you have some magic machine that I haven't had the opportunity of using yet, dump the first espresso out of the machine, whether it is the first cup when switching on or if the machine has been sitting unused for an hour or more (again just a guideline)
The golden rule I want to establish in this blog is 'the crema tells you everything'.
The crema on an espresso will tell you whether it is fit to drink without placing the cup anywhere near your lips.
The crema should be light golden colour. I recognise that it is slightly difficult to describe in words & publishing photos leads to chaos as everyone's screen shows colours slightly differently, but the following guide lines will at least get you into the 'zone' of espresso satisfaction, well on your way to nirvana.
Perhaps the easier way to describe the colour of the crema is what it shouldn't be.
Think of all the possible colours that the crema can adopt as a spectrum, ranging from whitish through the light golden colour already mention then on to the chocolate tones.
This colour spectrum is the espresso's built-in instrument panel telling you where in the range your espresso lies, all the way from chronically under-extracted (very light whitish tones) to chronically over-extracted (very dark chocolate tones). All you have to do is learn to read it by paying it a little more attention.
Once again, I am reluctant to dish out absolutes as my experience suggest that people's taste vary a little, but the key thing is to take note of the appearance of the crema before you taste the espresso, then taste it. If you like it, pause & take another good look at the remaining crema & commit it to memory. This is your target for next time.
Before we dive into under & over extracting, and what to do about it, lets talk about keeping the 'tail' out of your coffee. What's the tail I hear you ask?
The tail is just a word I have assigned to the light coloured splodge that will corrupt an otherwise perfectly drawn espresso right at the end. It will also be foamy/bubbly, unlike the extremely fine bubbles of the crema up to that point.
OK, great I hear you say, 'I have seen that bubbly white splodge on my otherwise perfect crema' but what can I do about it?
Well if you observe the stream of coffee as it flows from the bottom of the porta-filter you should see that it flows in a fairly continuous shape and then at some point just before the end of the extraction the stream will quaver or change shape. At this precise moment you need to quickly & carefully remove your cup out of the stream (by the time you have turned the button off it will be too late & the tail will still end up in your cup!)
But be careful - don't stick your eye so close to the machine that you are at risk of hot coffee spurting into your eye. Similarly when you deftly move the coffee out from under the stream do so in a smooth manner, not violently or you will most likely end up with hot coffee on your hand.
So, back to under & over extracting.
ANY WHITISH colour tones in your crema & you are under-extracting. What to do about it? Well, if you are only slightly off try tamping the coffee into the porta-filter with a little more vigour, or possibly place a little more coffee into the porta-filter. If this isn't enough, then set your grinder to a finer setting & try again. Yes, its trial & error, but not the rocket science that some would want you to believe.
ANY CHOCOLATE colour tones in your crema means it is over-extracted. What to do about it? The opposite of under-extraction. Possibly you have put in too much coffee, although you will usually be aware of this as you will struggle to get the porta-filter to locate onto the machine. More likely you have packed the coffee in with too much vigour. This is the most common scenario when you change to a Londinium coffee for the first time, as the coffee is so much fresher than most other coffee that there is a lot more oil still present in the bean which helps the grinds to stick together, unlike a stale coffee where the oils have long since departed and you are trying to force dry grinds to stick together. Failing that you might have to back your grinder off so it grinds slightly coarser.
...time is up for the moment, but those simple rules should get you well on your way to coffee nirvana.