How to get a head: In search of the perfect pint

We've been drinking beer for centuries. But only now are scientists learning the secrets of the perfect pint. Sanjida O'Connell learns the recipe for success from the master brewers

It's a drink that is almost as old as civilisation: beer was originally made from emmer, an early form of wheat, by the Babylonians who offered it to their gods. In this country, it was made mainly by women, known as beer witches; the last witch was burnt alive in 1591 for her bad brew. But until Louis Pasteur discovered that micro-organisms cause fermentation in 1860, no one understood what turned a gloopy slop of grain into a potent pint: brewers used to add beer from the previous batch and call it 'godisgoode'.

"It's a magical process," says Adrian Tierney-Jones, writer and beer expert. "Brewers never fail to be fascinated at how a beer turns from being lifeless to full of life." Alex Bell, head brewer for O'Hanlons, will explain to the Royal Institute tonight how scientists have finally got a handle on the magical alchemy of beer brewing. As Bell says, "The key thing in the brewing process is making alcohol." We now know it's the yeast that's responsible: it's a type of single-celled fungus, which produces the fizz and intoxication – alcohol and carbon dioxide. It takes 34 million of these cells to produce just one pint of beer.

The starting point for most beer is barley. The grains are soaked and then left to dry until they begin to germinate. To prevent them turning into mini-barley plants, the grains are heated and crushed. This malted barley smells of lightly toasted granary bread but the grain turns darker and richer at higher temperatures: crystal is a mixture that has toffee and biscuit flavours and roasted barley, used to make stout, looks and smells like ground coffee.

"What malted barley adds to beers are roasted and smoky aromas and coffee, chocolate, bready, biscuity, sweetcorn, hay, toffee, caramel and butterscotch flavours,"says Tierney-Jones.

The malted barley is heated with water to release enzymes that break the complex starches into simple sugars like glucose and maltose. Other enzymes chop the proteins in the grain into shorter segments. This wort, as it's called, is drained out and the remaining mashed barley is fed to the local cows. The wort is pumped into a brewing kettle where it's boiled with hops.

It was Belgian monks who first added hops to beer approximately 500 years ago. Before that a range of ingredients were used to impart flavour such as juniper berries and bog myrtle and even henbane, which is a hallucinogen. "The monks were allowed up to five litres of beer a day when they were fasting," says Bell, "so they took beer seriously."

The proper name for hops is Humulus lupulus; lupulus is derived from the Latin for wolf. A wild climbing vine, they're now grown by training them up 10ft vines. It's the flower, the "cone", that contains most of the unusual and complex chemicals that impart bitterness, aroma, antioxidants, enhance foam production and act as an anti-bacterial. Normally two types of hops are used – ones that add bitterness from humulone, an astringent acid – are boiled with the wort for at least an hour, whereas aroma hops are added towards the end of boiling so that they release their aromatic oils without the oils being evaporated. O'Hanlons uses dried hops from America, the UK and the former Czechoslovakia, which smell of Thai spice – of lemongrass, galangal and coriander. Tierney-Jones says, "Hops add herbal, grassy and lavender aromas as well as bitterness, spiciness and citrus, and tropical fruit flavours." The mixture is then left to ferment with yeast for up to five days. "After 24 hours, the yeast foam looks like a lemon meringue pie, the peaks are astonishing," says Bell. "What yeast adds to beers are the flavours and aromas of soft fruit," says Tierney-Jones. There are two main species of yeast: Saccharomyces cerevisiae, which works at warmer temperatures and is used to make bitter and ale, and Saccharomyces carlsbergensis, which needs cooler temperatures and creates lager. There are more than 500 strains of these two main species, often particular to a brewery. The larger brewers send their yeast to be stored in labs so that if anything goes wrong, they can recultivate their own strain.

Yeast converts the sugars from the barley into carbon dioxide, which gives beer its fizz, and alcohol. It's called the glycolytic pathway and its extremely metabolically inefficient as the yeast hardly recoups any energy from the process. "Yeast would gain more energy if it converted the sugars into carbon dioxide and water, as we do, but we're grateful that it doesn't," says Bell.

The by-products of this process are the production of other compounds that contribute to the flavour of the beer. For instance, the final step in the pathway is the conversion of glucose to the compound pyruvate. This is then converted into ethanal, which can then be turned into ethanol (alcohol); sometimes though, the ethanal gets converted to diacetyl. This chemical produces butterscotch flavours that are good in stout but not so welcome in other beers. Leaving the mixture for longer allows the yeast to turn the diacetyl into 2, 3-butanediol, which doesn't taste as strongly of butterscotch. Saccharomyces cerevisiae strains of yeast produce esters, such as isoamyl acetate, which tastes of pear drops and bananas, and ethyl hexenoate that has an appley aroma.

The beer is then put into casks or bottled and a secondary fermentation will take place that produces the carbonation. "There are so many factors that can change the finished product," says Bell, who has created a beer called Fire Fly, "the weather, the barley, which affects the range of proteins, the amount of oxygen in the beer that's added during mixing, the dynamic of the boil. The beer in your glass might not taste anything like you'd planned."

What determines whether a beer is an ale, a bitter or a larger is down to the amount and type of hops as well as the malted barley, but is primarily due to the strain of yeast. "A yeast that has been used for the same beer over a period of time will have a specific character and adds its own particular imprint to the beer. Different yeasts produce different flavours. O'Hanlons produce a beer that contains 12 per cent alcohol, lasts up to 25 years and is almost scarlet in colour when you hold it up to the light. It's named after Thomas Hardy, who wrote in The Trumpet-Major: "It was the most beautiful colour that the eye of an artist in beer could desire; full in body, yet brisk as a volcano; piquant, yet without a twang; luminous as an autumn sunset." Not quite what those Belgium monks might have expected from the action of a fungus and a wild wolf plant.

The Science of Beer by Alex Bell at the RI, this evening 7-9pm,; (020-7409 2992)

Suggested Topics
A 1930 image of the Karl Albrecht Spiritousen and Lebensmittel shop, Essen. The shop was opened by Karl and Theo Albrecht’s mother; the brothers later founded Aldi
Arts and Entertainment
Standing the test of time: Michael J Fox and Christopher Lloyd in 'Back to the Future'
filmA cult movie event aims to immerse audiences of 80,000 in ‘Back to the Future’. But has it lost its magic?
Arts and Entertainment
Flora Spencer-Longhurst as Lavinia, William Houston as Titus Andronicus and Dyfan Dwyfor as Lucius
theatreThe Shakespeare play that proved too much for more than 100 people
exclusivePunk icon Viv Albertine on Sid Vicious, complacent white men, and why free love led to rape
Arts and Entertainment
Stir crazy: Noel Fielding in 'Luxury Comedy 2: Tales from Painted Hawaii'
comedyAs ‘Luxury Comedy’ returns, Noel Fielding on why mainstream success scares him and what the future holds for 'The Boosh'
Life and Style
Flow chart: Karl Landsteiner discovered blood types in 1900, yet scientists have still not come up with an explanation for their existence
lifeAll of us have one. Yet even now, it’s a matter of debate what they’re for
Arts and Entertainment
'Weird Al' Yankovic, or Alfred Matthew, at the 2014 Los Angeles Film Festival Screening of
musicHis latest video is an ode to good grammar. But what do our experts think he’s missed out?
New Real Madrid signing James Rodríguez with club president Florentino Perez
sportColombian World Cup star completes £63m move to Spain
Hotel Tour d’Auvergne in Paris launches pay-what-you-want
travelIt seems fraught with financial risk, but the policy has its benefits
Arts and Entertainment
booksThe best children's books for this summer
Life and Style
News to me: family events were recorded in the personal columns
techFamily events used to be marked in the personal columns. But now Facebook has usurped that
ebookA unique anthology of reporting and analysis of a crucial period of history
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Sustainability Manager

Competitive: The Green Recruitment Company: Job Title: Scheme Manager (BREEAM)...

Graduate Sustainability Professional

Flexible, depending on experience: The Green Recruitment Company: Job Title: T...

Programme Director - Conduct Risk - London

£850 - £950 per day: Orgtel: Programme Director - Conduct Risk - Banking - £85...

Project Coordinator/Order Entry, SC Clear

£100 - £110 per day: Orgtel: Project Coordinator/Order Entry Hampshire

Day In a Page

Noel Fielding's 'Luxury Comedy': A land of the outright bizarre

Noel Fielding's 'Luxury Comedy'

A land of the outright bizarre
What are the worst 'Word Crimes'?

What are the worst 'Word Crimes'?

‘Weird Al’ Yankovic's latest video is an ode to good grammar. But what do The Independent’s experts think he’s missed out?
Can Secret Cinema sell 80,000 'Back to the Future' tickets?

The worst kept secret in cinema

A cult movie event aims to immerse audiences of 80,000 in ‘Back to the Future’. But has it lost its magic?
Facebook: The new hatched, matched and dispatched

The new hatched, matched and dispatched

Family events used to be marked in the personal columns. But now Facebook has usurped the ‘Births, Deaths and Marriages’ announcements
Why do we have blood types?

Are you my type?

All of us have one but probably never wondered why. Yet even now, a century after blood types were discovered, it’s a matter of debate what they’re for
Honesty box hotels: You decide how much you pay

Honesty box hotels

Five hotels in Paris now allow guests to pay only what they think their stay was worth. It seems fraught with financial risk, but the honesty policy has its benefit
Commonwealth Games 2014: Why weight of pressure rests easy on Michael Jamieson’s shoulders

Michael Jamieson: Why weight of pressure rests easy on his shoulders

The Scottish swimmer is ready for ‘the biggest race of my life’ at the Commonwealth Games
Some are reformed drug addicts. Some are single mums. All are on benefits. But now these so-called 'scroungers’ are fighting back

The 'scroungers’ fight back

The welfare claimants battling to alter stereotypes
Amazing video shows Nasa 'flame extinguishment experiment' in action

Fireballs in space

Amazing video shows Nasa's 'flame extinguishment experiment' in action
A Bible for billionaires

A Bible for billionaires

Find out why America's richest men are reading John Brookes
Paranoid parenting is on the rise - and our children are suffering because of it

Paranoid parenting is on the rise

And our children are suffering because of it
For sale: Island where the Magna Carta was sealed

Magna Carta Island goes on sale

Yours for a cool £4m
Phone hacking scandal special report: The slide into crime at the 'News of the World'

The hacker's tale: the slide into crime at the 'News of the World'

Glenn Mulcaire was jailed for six months for intercepting phone messages. James Hanning tells his story in a new book. This is an extract
We flinch, but there are degrees of paedophilia

We flinch, but there are degrees of paedophilia

Child abusers are not all the same, yet the idea of treating them differently in relation to the severity of their crimes has somehow become controversial
The truth about conspiracy theories is that some require considering

The truth about conspiracy theories is that some require considering

For instance, did Isis kill the Israeli teenagers to trigger a war, asks Patrick Cockburn