Before we start turning screws we have to understand what espresso actually is. Once you have grasped that, everything else suddenly makes sense. And you learn the most important thing straight away: your best measuring instrument is not the machine — it is your tongue.

Remember the five Ms? Mixture, amount, mill, machine, human being. Today we look at all five from above; in the next chapters we take each one on its own.

Which brings us to your most important tool — your tongue. Picture a horizontal axis: on the far left is sour, on the far right is bitter. And right in the middle lies your target — a round, sweetish, balanced espresso.

Hands-on: make yourself an espresso, no pressure at all. Take a sip and ask yourself just this one question: does it pull together at the front and sides, sharp and sour? Or at the back, hard and bitter? Or is it already pleasantly round? You do not have to change anything yet — just taste consciously for the first time.

There are two varieties that count: arabica and robusta. Arabica is the fine, aromatic one — with fruitiness, sweetness and lively acidity. Robusta is stronger, harsher, has more caffeine and produces a great deal of crema. Many espresso blends combine the two: plenty of arabica for the flavour, a dash of robusta for crema and body.

With roasting the rule is: the darker, the less acidity, the more roast bitterness and body. To start with, take a medium to slightly darker espresso roast — it is more forgiving. And remember: dark does not mean strong. Dark means bitter.

This is where guessing ends and weighing begins. A proven starting point for a double espresso: eighteen grams of ground coffee in, thirty-six grams of espresso out — a ratio of one to two. So you weigh not only the beans beforehand but the cup afterwards as well.

Why so precise? Because only numbers make your espresso repeatable. A small barista scale accurate to a tenth of a gram is the cheapest big improvement you can make.

It controls how fast the water runs through the coffee. Grind coarser and the gaps are bigger — the water rushes through too fast and takes too little with it: thin and sour. Grind finer and the resistance grows, the water dissolves more. Go too fine and everything clogs up and it turns bitter.

So the rule is: coarser when it runs too slowly and bitter. Finer when it runs too fast and sour. Those two sentences are half your barista life.

This is the most instructive exercise of the whole course. Set your grinder deliberately too coarse and pull an espresso — it rushes through, pale and watery. Then go markedly finer: now it drips thickly, dark and slow.

Taste both. One sour and thin, the other bitter — and somewhere in between lies your point. You do not have to hit it perfectly today. You are meant to see with your own eyes and your own tongue how much one small turn moves.

Two things make the difference between “coffee” and “espresso”. The first is the group head — the heavy piece of metal through which the hot water is forced. On a good machine it is solid: that mass stores heat and provides a stable temperature right at the brew head.

The second is PID temperature control: it holds the brew temperature constant to within a few degrees. Weaker machines swing by ten degrees — and ten degrees is the difference between sweet and bitter. A good starting value is around ninety-three degrees.

Your espresso is more than ninety per cent water — do not use hard, heavily chlorinated tap water, use filtered or soft water. You can taste it, and your machine scales up more slowly.

And the steam wand — the movable metal arm we later use to foam milk. One important habit from today on: after every foaming, wipe the wand at once with a damp cloth and blow it through briefly. Dried-on milk is otherwise almost impossible to remove.

Four steps, always in this order. One, dosing: your eighteen grams go into the basket as evenly as possible. Two, WDT: with a tool of fine needles you go through the grounds and break up every clump — the most effective trick against uneven extraction.

Three, levelling: spread the surface smooth and even. Four, tamping: press the grounds down firmly — and here only one thing counts: level. Not especially forceful, but absolutely horizontal, the tamper set down flat. Your puck is ready.

And now for the best learning tool there is: the bottomless portafilter. Its bottom is open, you watch the coffee run out from below — and it shows you every mistake without mercy.

If the stream runs nicely from the centre and joins into one thread — perfect. If it drips on one side only — your tamp was crooked. If it sprays wildly — that is channelling. The bottomless portafilter is your most honest teacher. It makes the invisible visible.

You need three anchors, and you already know two. First the amount in: eighteen grams, weighed. Second the amount out: thirty-six grams, a ratio of one to two. And third, new: the time — a good espresso runs through in about twenty-five to thirty seconds, from the moment you start the pump.

Those three together are your recipe. And usually it is the time that is off — and you control that, as you might guess, through the mill.

Pull an espresso with your eighteen grams and take the time. Taste it and look at the clock. Too fast and sour? Set the grinder one step finer and pull again — change the mill only, nothing else.

Feel your way, attempt by attempt, until you land at twenty-five to thirty seconds and a round taste. And then, very important: write down the bean, the grinder setting and the time. That is your recipe for exactly this bag.

Two things happen one after the other when you foam milk. First you draw air into the milk — that makes volume and foam. Then you roll that air into very fine bubbles until nothing coarse is left. Air in first, then roll it fine.

You steer this with your ears. Phase one, drawing air: wand just below the surface, open it up — a gentle, regular hiss, each one a small sip of air. Lower the jug slowly as the milk rises.

Cold jug, cold milk, up to the spout. Wand just below the surface, open it up — and listen to the hiss. Draw air for a few seconds, lower the jug slowly. Then wand deeper, tilt the jug, look for the whirlpool.

Feel the warmth. Is it glossy? Then stop. Wipe the wand. Forget latte art at the beginning — practise the consistency only: glossy, silky, no coarse bubbles.

Listen closely, this is the most important minute: latte art is ninety per cent the result of good espresso and good microfoam — and only ten per cent hand movement. Without a decent crema the brown canvas is missing. If the foam is too stiff it plops in as a lump; if it is too liquid the pattern sinks.

Which means: before you think about pouring, chapters six and seven have to sit — round espresso, glossy microfoam. Get the basis right and the pattern almost comes by itself.

You now have all the building blocks — espresso, water, milk, foam. The secret is simple: almost every drink is just a different ratio of those four things.

In the middle stands the espresso — neat, the core of everything. Let less run through with the same amount of coffee and you get a ristretto: shorter, denser, more intense. Let more water run through and you get a lungo: longer, milder. An americano is espresso with hot water, a cortado mild with a little milk.

A well-kept machine is half the battle — dirty baskets, old coffee oils and limescale can be tasted. Care runs in three rhythms, and then you never forget anything.

First rhythm, after every shot, thirty seconds: briefly flush the group head, wipe the steam wand and blow it through — the most important movement — and knock out the portafilter. Add a weekly backflush and, now and then, a descaling run.

If something does get stuck: no pressure and the espresso only drips? Usually ground too fine — grind coarser. No crema? Beans too old, or machine and cup too cold — back to freshness and heating up. Milk will not foam? Wand blocked or milk not cold.

Espresso suddenly tastes different? A new bag of beans — you have to dial in again. You see: almost every problem leads back to one of the five Ms, and you now have all of them in hand.