Module F2, How beer is made

F2.1.1 Sprouting and kilning

Two steps, about a week, and the grain arrives at the brewery already carrying its flavour.

A grain of barley is a seed packed with starch. Yeast cannot eat starch. It can only eat sugar, and the barley will not hand over its starch to anyone until it thinks it is about to become a plant.

Malting is the trick that solves this. You convince the seed it is spring, let it start growing, then stop it. It happens at a maltings, not at the brewery, and most breweries buy their malt already made.

1. Steeping. The barley is soaked in water for a day or two, until it takes on enough moisture to wake up.
2. Germination. It is spread out and kept cool and damp for four or five days. The seed sprouts, and while it does, it produces the enzymes that will break its own starch down. It also softens the hard interior.
3. Kilning. Hot air is blown through to dry it out. This stops the growth before the sprout eats the starch you wanted, and it locks everything in place.

The whole process takes about a week. The timing of the stop is the point: you want the seed to have made the enzymes and softened the starch, but not to have started spending it.

The kiln sets colour and flavour together

How hot that kiln runs, and for how long, decides what the malt looks like and what it tastes like. Those two are not separate decisions. They are the same decision.

The browning here is the same reaction that browns toast, roast potatoes and a seared steak. Heat, sugar and protein together produce hundreds of new compounds, and they smell of exactly what you would expect: bread crust, caramel, coffee.

F2.1.2 Base malt and speciality malt

Most of the grain does the work. A small fraction does the talking.

Base malt is the engine. It brings the sugar and it brings the enzymes, and without enough of it there is nothing to convert the starch in anything else. A recipe can be all base malt and nothing else. A recipe cannot be all speciality malt.

Speciality malt is the seasoning, and a very small amount goes a long way. A few percent of black malt will turn an entire batch dark. That is why a beer can look like liquid tar and still be built almost entirely from pale grain.

One speciality malt is worth knowing by name. Crystal malt, also sold as caramel malt, is heated while still wet so the sugars inside caramelise into a hard glassy centre. It brings toffee, a copper colour, and body. Many of its sugars cannot be fermented, so they stay in the finished beer and make it feel fuller.

This is a genuine dividing line between styles. An English bitter or an amber ale leans on crystal malt for its toffee note. A modern West Coast IPA uses almost none, because that sweetness would blunt the hops.

F2.2.1 Starch into sugar

One hour, one vessel, and the step that turns grain into something yeast can eat.

The malt is crushed, not ground to flour. You want the hard interior broken open and the husk left more or less intact, because the husks form a natural filter bed later.

The crushed grain goes into a vessel with hot water and sits there for 45 to 90 minutes. Somewhere around an hour is normal. This is the mash.

Inside it, the enzymes the barley made while sprouting go to work. They cut the long starch chains into short sugars. It is a slow, quiet, unspectacular step that looks like a vat of porridge and does most of the chemical work in brewing.

What you draw off at the end is a sweet, sticky liquid called wort, which is said WERT. Think of it as unfermented beer. It tastes like very sweet grain tea and no alcohol has been made yet.

The grain bed still holds a lot of sugar at that point, so the brewer rinses it with more hot water to collect the rest. Then the spent grain gets shovelled out, and it usually goes to farmers as cattle feed.

F2.2.2 The temperature dial

Same grain, same yeast, two very different beers. The variable is a few degrees in the mash.

Two different enzymes are doing the cutting, and they like different temperatures. That is the whole mechanism, and it gives the brewer one of the most powerful controls in the process.

The cooler enzyme works best around 145F to 150F, which is 63C to 66C. It makes small, simple sugars, and the yeast can eat every one of them. The result is a dry, thin, crisp beer with slightly more alcohol.

The hotter enzyme works best around 154F to 158F, which is 68C to 70C. It leaves behind larger sugar chains called dextrins, which just means sugars too big for the yeast to eat. They stay in the finished beer, so it feels fuller and rounder and ends up slightly weaker.

This is why body and sweetness are not the same as sugar added to the beer. A milk stout feels thick partly because it was mashed hot. Nobody stirred sugar into it at the end.

F2.3.1 Why brewers boil

Five jobs in one hour, and a trade that runs through the whole of modern brewing.

The wort comes off the grain sweet and vulnerable. It goes into a kettle and boils hard, usually for 60 minutes, sometimes 90.

• It sterilises the liquid, so nothing but the chosen yeast gets to grow in it.
• It stops the enzymes, which locks in the balance of sugars the mash produced.
• It drives off a compound from the malt that would otherwise smell of cooked sweetcorn. Brewers call that fault DMS, and a short or covered boil is the usual cause.
• It concentrates the sugar, because water evaporates.
• It creates bitterness, if hops are in the kettle.

Bitterness needs sustained heat

Hops arrive carrying bitter compounds that barely dissolve in liquid as they are. Boiling rearranges them into a form that does dissolve, and that form tastes bitter. Brewers call this isomerization, which just means the molecule getting rebuilt into a different shape with the same parts.

The important part is that it is slow. It needs sustained heat, not a moment of it. A 60 minute boil converts roughly 20% to 35% of the bitter acids in the hops. Most of what you paid for goes down the drain, and boiling for longer buys steadily less.

And smell does not survive it

The aromatic oils in hops are volatile, which is exactly why you can smell them. Boiling drives them straight out of the kettle. The most abundant one is called myrcene, and it halves about every five minutes of boiling.

Five minutes takes out half. Ten minutes takes out three quarters. After an hour there is essentially nothing left of it. The brewery smells wonderful and the beer will not.

F2.3.2 The four addition points

Four places hops can go in, from hardest boil to no heat at all.

A modern IPA usually uses three or four of these in the same beer. That is why smell and bitterness can be set independently. Some IPAs smell enormous and taste restrained, and others do the opposite, and the brewer chose which.

It also explains a change in how beer is made. In 1990 most of the hops in an American IPA went in at the start. Today most of them go in at the end or cold, because drinkers turned out to want the smell more than the bitterness.

F2.4.1 Yeast eats sugar

The only step where alcohol appears, and the step where most of a beer's personality is decided.

The boiled wort is cooled quickly, then yeast is added. Brewers call that pitching. From there the yeast is in charge and there is not much anyone can do except hold the temperature steady.

1. A quiet period of a few hours to a day. The yeast is taking in oxygen and multiplying, not making alcohol yet.
2. Active fermentation. The surface foams up, the liquid churns, carbon dioxide pours off, and the temperature climbs on its own because fermentation gives off heat.
3. It slows down. The sugar runs low, the foam falls back, and the yeast starts tidying up compounds it made earlier.
4. It settles. The yeast drops out of suspension and the beer begins to clear.

That third step matters more than it sounds. Yeast produces a butter or butterscotch flavour early on, called diacetyl, and then reabsorbs it if you leave it alone long enough. Chill the beer too soon and the butter stays. A slick, buttery pale lager is a beer that was rushed.

Warm and fast, or cold and slow

A few degrees changes the beer noticeably. Warmer yeast makes more of the fruity compounds called esters and more of the spicy ones called phenols. A Hefeweizen brewer ferments at the top of the ale range to push the banana up. An IPA brewer ferments at the bottom of it to keep the yeast out of the way.

Fermentation produces heat, so left alone a vessel would run away with itself and get hotter and fruitier as it went. Breweries wrap their tanks in cooling jackets to hold the number steady. Temperature control is most of what separates a good fermentation from a rough one.

F2.4.2 Attenuation, esters and phenols

How much sugar got eaten, and what the yeast left behind besides alcohol.

How dry the beer ends up

Attenuation is the proportion of the sugar the yeast managed to eat. It is the number that decides whether the beer finishes dry or sweet, and you can work it out from the two gravity readings.

Three things set it between them: the mash temperature, the yeast strain, and whether any plain sugar went in. Plain sugar ferments completely, so Belgian brewers use it to make a strong beer that still finishes dry rather than sticky.

What else the yeast leaves

Alongside alcohol, yeast makes fruity compounds called esters and spicy ones called phenols. Banana, pear, apple and pineapple are esters. Clove, pepper and a faint smokiness are phenolic, which is simply the adjective for that group.

Whether they count as a fault depends entirely on the style. Clove is the point of a Hefeweizen. In a pale lager the same compound reads as sticking plaster and means something went wrong.

One more thing yeast decides is how clear the beer ends up. Brewers call it flocculation, which just means how well the yeast clumps together and drops to the bottom when it has finished. English strains do it well and the beer falls bright. Hazy IPA strains do it badly on purpose, and the beer stays cloudy.

F2.5.1 Settling, clearing and bubbles

A rest, then a decision about where the bubbles come from.

Beer straight out of fermentation is not ready. It is cloudy with yeast and protein, it has very little carbonation, and it carries rough edges the yeast has not finished cleaning up. Conditioning is the rest that fixes all three.

For an ale that can be a few days to a couple of weeks. For a lager it is much longer, and it has a name. Storing a finished lager cold for weeks is called lagering, from the German word for storing. Traditionally four to twelve weeks near freezing. Many modern breweries do two to four.

How beer clears

• Gravity. Given time, yeast and protein simply fall to the bottom.
• Cold. Chilling hard makes hazy particles clump and drop faster.
• Finings. A substance added to gather the haze and pull it down. The traditional one is isinglass, made from fish swim bladders, which is why some cask ale is not vegan. Modern alternatives are.
• Filtration. Physically straining the beer bright. Fast and reliable, and it strips a little flavour with the haze.

A hazy IPA skips all of this on purpose. The yeast is chosen not to settle, the beer is not filtered, and the cloudiness is part of the product rather than a failure.

Two ways to get the bubbles in

Carbonation is measured in volumes of carbon dioxide, and the range across beer is wider than most people expect. Cask ale sits around 0.75 to 1.3 volumes, which is barely fizzy. British ales run 1.5 to 2.0. American lagers run 2.5 to 2.8. German wheat beers and many Belgian styles go to 3.5 to 4.5, which is more carbonated than most sparkling water.

F2.5.2 Cask, keg, can, bottle and nitro

The container is not just packaging. It changes the temperature, the fizz and how long you have to drink it.

What nitro actually changes

Nitrogen barely dissolves in beer, so it comes out as very small bubbles instead of the coarse ones carbon dioxide gives. Forcing the beer through a plate full of tiny holes on the way out creates the cascade and the thick head.

The result is a change in mouthfeel, which just means how the beer feels rather than how it tastes. It comes out creamy and soft, with far less of the prickle that carbonation gives. It also mutes bitterness and aroma, which is why nitro suits stouts and milds and does an IPA no favours.

For taking beer home, the ranking is simple. Cans beat bottles because light cannot get in. Brown bottles beat green and clear ones for the same reason. And any hoppy beer should be bought as fresh as you can find it, because the smell is the first thing to go.