Tastings School - That special something (Yeast)

Tastings School

From basics to more advanced topics, the Beer School has all the info to expand your knowledge and enjoyment of your beers, ales and lagers.

Categories

That special something (Yeast)

Yeast is a vital and complex part of beer production. Roger Protz looks at the history of this ingredient and how brewers keep it happy

What are the essential ingredients used in the production of beer?

Barley malt, of course, and other grains and special sugars that combine to make a sweet extract known as wort.

Then hops, the salt and pepper of the process, add piny, resiny, spicy and fruit aromas and flavours. And there is water, not any common-or-garden tap water, but pure liquor, often drawn from deep underground wells or bursting from the ground from natural springs. Even when water does come from the public supply it is purified several times before it is deemed fit for purpose.

But if a brewer makes a hopped wort from these three ingredients, we still would not have beer. It takes something special, almost magical, to turn malt, hops and water into a pleasurable and life-enhancing form of alcohol. That something special is yeast.

Unknown to the ancients in the Old World of Babylon, Egypt and Mesopotamia, it was wild yeast spores in the air that turned a sweet liquid derived from the bread-making process into a drink that encouraged a Sumerian poet around 3000 BC to write, “I feel wonderful, drinking beer/in a blissful mood/with joy in my heart and a happy liver.” The role and behaviour of yeast was not understood until modern times. In medieval England, brewers called the froth on wort that produced ale “God-is-good” as it seemed to be manna from heaven.

It was not until the 18th and 19th centuries when first the Dutch scientist Anton van Leeuwenhoek and then the French micro-biologist Louis Pasteur analysed yeast that its role in brewing was finally grasped.

With the aid of a microscope, Pasteur was able to demonstrate that the production of alcohol was not a miracle but a natural chemical reaction in which yeast cells multiplied as they turned sugars into alcohol and carbon dioxide. Thanks to Pasteur’s microscope, the next stage in our understanding of brewer’s yeast came in the Carlsberg laboratory where a pure strain, free from harmful bacteria, was isolated by the brewing scientist Emil Hansen.

As lager beer became the dominant style in the 20th century, the world of brewing divided into two yeast camps: saccharomyces cerevisiae or ale yeast, and saccharomyces carlsbergensis or lager yeast, named in honour of the Carlsberg research work.

More commonly, the styles are known as top fermenting and bottom fermenting, as ale yeast tends to create a thick head on top of the fermenting beer, while lager yeast gradually falls to the foot of the vessels. But the distinction is less clear today, as many brewers produce ale in upright conical vessels rather than traditional open ones and, as a result, the yeast is cropped from the bottom of the vessels, rather than the top.

Nevertheless, yeast, a single cell fungus, remains a volatile element in the brewing process. Brewers carefully nurture and culture their house yeasts and keep supplies in a national yeast bank in case the unthinkable – infection – strikes and a brew has to be destroyed and a new one started with fresh yeast.

And yeast has its prima donna side: it can refuse to produce alcohol and is often unhappy about being moved from one brewing site to another. It is also fussy about the ingredients it works with. A brewer at Marston’s in Burton-on-Trent once told me that when he switched from Maris Otter to Pipkin malt, his yeast strain sulked and worked sluggishly, forcing the company to return to Maris Otter.

The question of beer flavour and yeast behaviour has become a hot topic as a result of a crop of closures among regional breweries in Britain. Beer brands have moved from closed breweries to the sites occupied by their new owners.

Greene King, for example, has acquired the brands of Morland, Ridley’s and Ruddles and more recently has bought and closed Hardys & Hansons in Nottingham. Many of the beers from those former breweries – including the best-selling Morland’s Old Speckled Hen and Ruddles County – have been recreated at Greene King’s plant in Bury St Edmunds, Suffolk.

The leading London brewer, Fuller’s of Chiswick, bought and closed George Gale & Co in Hampshire in 2006 and has transferred some of the beers to London, including the premium bitter HSB.

More recently, and to great consternation among London drinkers, the revered Young’s brewery has closed and moved production to another substantial regional brewer, Charles Wells in Bedford.

The controversy surrounding all these events prompts the question: is it only British beer lovers who feel that beers lose their credibility when they move to a new site? I have drunk Samuel Adams’ “Boston” ales in airports at Dallas and St Louis and they were superb. And yet when one of my favourite English ales, Wethered’s Bitter, was transferred from Marlow to McMullen’s brewery in Hertford it became a different beer, losing its profound orange fruit character, even though both breweries used a yeast culture that came originally from Whitbread.

Ken Don, the experienced head brewer at Young’s, has overseen the transfer of Young’s beers to Bedford in close co-operation with Wells’ head brewer, Jim Robertson (pictured above). Young’s ales were fermented in conventional open square fermenters whereas Wells uses conicals for both ale and lager. Ken started his career at the Alloa Brewery in Scotland, a Dutch-style lager plant with fermentation in conical vessels, so he is experienced at handling both open vessels and closed ones.

“The Young’s yeast behaved well at Bedford,” he said. “Moving ale from squares to tall conicals isn’t always successful, but the Wells’ conicals are squat, not tall, and are not unlike the squares at Young’s. Our yeast didn’t produce any sulphur, which was one of my concerns when we moved.

The only difference in technique is that we now crop the yeast from the bottom of the conicals.” Charles Wells, in common with many brewers who use an ale yeast in conicals, replaces the yeast with a fresh batch after a number of brews to prevent the culture mutating into a true lager yeast and changing the complexity and character of the beer. Ken Don said this did not present a problem for him, as he replenished the yeast at Young’s after every nine brews.

Ken pointed out that Wells has a wealth of experience of looking after many yeast strains. As well as its Eagle Bitter and Bombardier ales, the Bedford brewery produces Cobra, Kirin and Red Stripe lagers. A specialist micro-biologist looks after all the cultures, including those used to ferment Young’s bottle-conditioned beers. It is worth noting that while the Young’s beers produced at Bedford are largely devoid of sulphur, Wells’ ales have always had a decidedly sulphury aroma, proof that the beers have maintained their separate characters.

John Bexon, head brewer at Greene King, said his scientific team propagate yeast cultures for such famous ales as IPA and Abbot. “When we get yeast from a third party, we always re-propagate the yeasts and use them as freeze-dried cultures.” It is difficult to say whether Greene King has achieved exact matches for beers it has acquired, as Ruddle’s County has been decreased in strength from 5% to 4.4% and, more recently, the draught version of Morland’s Old Speckled Hen has been dropped from 5.2% to 4.3%.

A fascinating example of transferring yeast and making strenuous efforts to reproduce correct aromas and flavours can be seen at O’Hanlon’s Brewery in Whimple, Devon. John O’Hanlon, a Dubliner, first brewed in London then decamped to Devon in 2000 where he brews his award-winning ales, including Firefly, Champion Wheat, Dry Stout and the remarkable Port Stout, which is based on an old Dublin recipe and includes a dosage of port wine in every batch of beer.

Along the way he picked up two celebrated beers from the defunct Eldridge Pope brewery in Dorchester, Royal Oak and the world-famous strong beer, Thomas Hardy’s Ale.

John knew he had to precisely recreate the amazing character of Thomas Hardy’s or face retribution.

He was aided by Dan Thomasson, the former Eldridge Pope head brewer who now works for the Hampshire Brewery in Romsey, but retains a great passion for the 11.7% old ale he brewed for several years.

Eldridge Pope closed in such a rush in 1996, turning itself into a pub-owning retailer, that such matters as yeast cultures were lost or displaced. Fortunately, the family-owned Palmer’s Brewery in Bridport shared the yeast with the Dorchester company and was able to supply O’Hanlon.

Thomas Hardy’s Ale, with a mighty starting gravity of 1125 degrees, is not a cooking bitter: the finished product is meant to be laid down for at least nine months and will stay in drinkable condition for a further 25 years. It is made from Pipkin pale malt and a touch of crystal: the ruby colour comes from some caramelisation of the brewing sugars during the long copper boil. The hops used are a massive dose of Challenger, Goldings, Northdown and Styrian Goldings, which recreate 75 units of bitterness.

The yeast is pitched and repitched three or more times during primary fermentation to prevent it from going to sleep and not producing sufficient alcohol. But the conventional ale yeast is not sufficiently robust to handle three months of secondary fermentation followed by a month of cold conditioning prior to bottling. The yeast used for this lengthy process is a German lager yeast acquired by Eldridge Pope when it brewed a strong lager called Faust. Both the cultures are stored in freeze-dried form by O’Hanlon.

The ale was first brewed to commemorate a literary festival in Dorchester to celebrate the life and work of Thomas Hardy, who lived in the area.

He described the beers of the town he called Casterbridge in his Wessex novels as “brisk as a volcano, full in body, piquant…luminous as an autumn sunset.” Quite what he would make of a beer named in his honour but brewed with the help of a German lager yeast is anyone’s guess but it survives for our continued delectation.