The science and magic of… beer

Andy Connelly
Friday 29 July 2011

From man’s sweat and God’s love, beer came into the world.”

St Arnold

We are the sons and daughters of malt. The cry “fancy a pint?” is the most natural social invitation available to us. Beer is our social lubricant of choice and has been for centuries.

Yet how many of us spend as much time over our selection of beer as we do our selection of wine? Whereas fermented grape juice is seen as something foreign or exotic, beer is often gulped down without giving a moment’s thought to the potent skills of the maltsters and brewers who created it. Little consideration is given to the incredible range of flavours available to us; flavours that can be harnessed to match our mood and the food on our plates.

Beer is the juice of grain skilfully treated: it is liquid bread. The first people to make beers as we know them today were the Sumerians, who cultivated cereal grains specifically for brewing and drank beer to honour their gods. Many cultures have seen beer as a gift from God (a medieval English term for yeast was godisgoode). It is an expression of place and tradition – one of the few truly regional foods to which we are regularly exposed.

Brewing is a combination of art and science and great brewers are blessed with a little of both. The artist in the brewer chooses the ingredients and balances the flavours and aromas of the finished product. The scientist understands and carefully orchestrates a symphony of chemical reactions between the grain, the water, the hops, and the yeast. The brewing process is complex and what follows can only be an outline of it.

Making the malt

To make beer and wine alcoholic we need sugar, the foodstuff that yeast transforms into alcohol. The fruit used in winemaking naturally accumulates sugar to attract animals and so spread its seed. By contrast the grain used for making beer is sugarless. Instead, grain is filled with starch, which provides energy for the growing embryo/seedling. This starch must be processed to form the sugars that yeast can then use.

While the requirement to produce sugar from grain adds complexity to the brewing process it also offers the brewer an enormous amount of control over flavour and texture – a type of control the vintner doesn’t have.

Enzymes – biological catalysts that speed up chemical reactions without themselves being consumed – are used to extract sugar from grain. When Inca women chew grain to make chichi, a maize beer, they’re using the enzyme amylase in their saliva to break down the starch.

In the Near East, where British-style beer originated, ancient brewers discovered that the grain itself could supply such enzymes during germination. Barley was found to be particularly good at producing them and so it became the grain of choice for beer making.

To trigger production of these naturally occurring enzymes and transform the starch stored in the grain into sugars, the raw barley is encouraged to germinate by soaking it in cool water for a few days then allowing it to dry.

The maltster stops this process dead by placing the germinated grain (the malt) in a kiln, where heat and desiccation kill the embryo but preserve the wonderful chemistry ready for the brewer.

To produce malt for a pale yellow, light-flavoured beer, the maltster dries the barley gently at 80C, creating a “pale malt”. If the temperature is increased, an incredible range of complex chemical reactions begin to take place.

Alongside the caramelisation of sugars, we see complex Maillard reactions between sugars and amino acids (the building blocks of protein) in the grain (the same “browning” reactions occur when a joint of meat is roasted in an oven and when bread is toasted). The higher the temperature and longer the heat exposure, the darker in colour and richer in flavour and aroma the malt becomes.

Very high temperatures (150-180C) create malts that are especially dark and flavoursome. Words used to describe such malts include: “caramel”, “chocolate”, “rich” and “black”. These malts create the iconic style of dark and heavy beers, such as porters and stouts.

Making the wort

The roasted malt is ground and then loaded into a vessel called a mash tun. Water is added and the mixture is heated, drawing out sugars and other chemicals from the malt and encouraging more enzyme activity. The “wort” that results from this soaking in water is a sweet, brown, earthy liquid.

The first stage of the mashing process above sounds innocuous “water is added” but it is very important. As Pliny the Elder wrote:

Alas! What wonderful ingenuity vice possesses! A method has actually been discovered for making even water intoxicated.”

Water is what makes a beer “local”. Even the strongest beers are 85-90% water, so the flavour of the water – a product of the local environment and geology – has a direct impact on the flavour of the beer.

Early brewers tailored their beers to make the best of local waters. Thus, in sulphate-rich Burton-on-Trent English pale ales were developed as the bitterness of the water limited the use of hops. The mild water of Pilsen encouraged Czech brewers to add large amounts of hops. The alkaline, carbonate-rich waters of southern England and Dublin balanced the acidity of dark malts and so encouraged the development of darker beers.

In modern times, some brewers use additives to control the chemical composition, and so the flavour, of their water making it no longer truly “local”.


At this stage hops are added to the wort and the two are boiled together in beautiful shiny coppers.

Until the 11th century, beer was drunk without hops. This would be an unpleasant experience to modern palates. Un-hopped beer is at best cloyingly sweet and at worst it has turned eye-wateringly sour due to the growth of unwanted bacteria.

To get over these problems brewers used plants, herbs or spices to add aroma, bitterness, and to help prevent (or perhaps cover up) bacterial infections. Additives included meadowsweet, rosemary and bog myrtle.

Unfortunately, these were not very successful, not least due to difficulties in cultivating such plants. From around the 8th century hops started to be used in central Europe. They were relatively easy to cultivate, being grown in Kent by the 1520s, and ideal for adding bitterness and aroma. They also had great disinfectant properties.

Hops are a member of the hemp family. The flower or cone of the hop contains alpha acids, beta acids, tannins and oils. The proportion of these depends on hop variety. Alpha acids give bitterness to beer while the oils impart aroma. The beta acids and tannins in the cone help to stabilise the beer and have vital disinfectant qualities.

Hops are either added at some point during the boil or after. If the hops are added earlier they provide greater bitterness, if they are added later the essential oils do not evaporate and so remain in the beer, adding aroma. Well hopped beer can have strong floral, resiny, and/or citrusy notes.

After boiling the brewer has transformed bland, dry, sugarless barley grain into a rich, bittersweet liquid that frankly tastes disgusting. To transform this swamp water into the perfect pint, yeast cells have to go to work.


After the wort has been cooled and aerated, yeast is added and so fermentation begins.

The process of fermentation is generally split into two main stages. At the beginning of the first stage there is plenty of oxygen available and so yeast cells can reproduce very easily. However, alcohol is not produced in this process. As the oxygen supply is exhausted the reproduction of yeast cells slows, but fermentation begins as sugars are transformed into ethanol and carbon dioxide.

Fermentation is the transformation of sugar into alcohol (ethanol) and carbon dioxide by yeast. In addition to alcohol, yeasts produce many other flavour and aroma compounds including esters, fusel alcohols, ketones, phenols, and fatty acids. Esters are the compounds responsible for the fruity notes in beer, while phenols can cause spicy or smoky notes. Brewers use their own specially selected and carefully controlled yeast strains to produce the distinctive styles of their own beers.

Before we understood the fungal nature of yeast, traditions and superstitions had to be relied upon. Viking families would have a “brew stick” which they used for stirring the wort and which magically started its transformation into beer.

We now understand that this stick was covered in dormant yeast cells and that stirring the wort introduced air into the beer and transferred the yeast cells. These brewing sticks were family heirlooms – a yeast infection passed down from generation to generation, if you will.

It took scientists such as Louis Pasteur to take yeast from the metaphysical realm into something that we can now understand and manipulate.

There are two basic styles of brewer’s yeast: ale and lager. Ale yeast (Saccharomyces cerevisiae – “sugar fungus ale”) works at warm temperatures (15-25C) in the brewery and forms a vast blanket of froth on top of the wort. This type of yeast does not turn as many sugars into alcohol as lager yeast, so leaving a residual sweetness. It also lends a certain hearty fruitiness to the aroma and palate.

Lager yeast is classified as S. carlsbergensis because the first pure culture was isolated at the Carlsberg brewery in Copenhagen. Lager brewing began is central Europe in the 15th century when brewers in Bavaria stored – or lagered in German – their beers in deep, icy caves to keep them in drinkable condition during the long hot summers. From this evolved cold-tolerant lager yeasts that also turn more sugar into alcohol, giving a dryer beer.


In the first stage of fermentation the yeast cells use up most of the easily fermentable sugars. After this the second stage begins. Fermentation slows and the yeast starts to work on the heavier sugars such as maltotriose. This is referred to as conditioning.

Conditioning can take place in different situations depending on the type of beer. The traditional beer style of Britain, real ale, is simply “racked” (poured) into the cask. This “cask-conditioned” beer leaves the brewery in an unfinished state because final conditioning takes place in the pub cellar where yeast in the cask continues to turn the remaining sugars into alcohol.

As the beer matures it gains not only a small amount of additional strength but also develops round and fruity flavours. Conditioning can take from two to four weeks, sometimes longer depending on the type of beer.

Lagers are usually aged in large tanks in the brewery at near freezing temperatures (just like those in the Bavarian caves) for one to six months depending on style. This cold ageing serves to reduce sulphur compounds produced by the yeast, helps clear the beer, and produces a cleaner tasting final product with fewer fruity esters.

Lagers are usually pasteurised prior to delivery. This means that unlike cask-conditioned ale, lagers (and cream flow ales) are biologically dead when they arrive at the pub.


For me beer isn’t just meant to be drunk on its own. Beer and food make great table fellows. I love to match the citrus/grapefruit style of a hoppy Indian pale ale, or a good hoppy lager, to the spice of a curry; or make use of a well-roasted dark malt stout to complement a rich chocolate dessert.

Wherever you are drinking your beer, though, make time for an appreciative pause. Take up your glass and salute the work of those who turn the sugarless, aroma-less, dry grains into the wonderful, multifaceted liquid we see before us. Drink deeply and enjoy.

Further Reading

How to brew – Palmer
McGee on food and cooking – Harold McGee
Radical brewing – Randy Mosher
The Cambridge World History of Food

Image by Michael Fajardo (


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