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Vineyard to farmyard
THE LAST WORD Bottle it Beer is usually packaged in brown bottles. Apparently this is because if it is packaged in clear glass, sunlight can damage its flavour. But how does sunlight damage beer? What chemistry occurs?
n I’m a student who has recently developed an obsession with home-brewed beer, so I hope I can offer some insight. Nearly all beer contains hops. This provides the bitter taste and
“UV light causes beer to develop thiols – the sulphur analogue of alcohols – causing a skunky flavour” also acts as a preservative (some natural deodorants even use hops for its antimicrobial action). Hops contain isohumulones, which provide part of the bitter flavour – and this is where the problem with light arises. When UV light hits these compounds they decompose, leading to the creation of free radicals that react with sulphur-containing amino acids. The product is a thiol – the sulphur analogue of alcohols – and this leads to a “skunky” flavour, so called for obvious reasons. To protect against this, manufacturers use brown bottles that block out some of the UV rays. Clear and green bottles offer far less protection and so are more prone to develop a skunky flavour. Try leaving a glass of beer out in the sun for even 10 minutes and
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of answers published in the magazine will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material that has been submitted by
Last words past and present at newscientist.com/topic/lastword
compare it with one not in direct sunlight, and you will get an idea of what skunky beer tastes like. Robert Law Duffield, Derbyshire, UK n Visible and UV light causes a reaction in which riboflavin (vitamin B2) acts as a catalyst to break down bitter compounds called isohumulones that come from hops. This creates free radicals. One of these, 1,1-dimethylallyl, can then take a thiol group from a sulphurcontaining amino acid to become 3-methylbut-2-ene-1-thiol. This compound is similar to two of the sulphurous compounds in a skunk’s spray, namely 2-butene-1thiol and 3-methyl-1-butanethiol. Brown bottles cut out most of the harmful wavelengths of light so beer does not become “skunked”. Eric Kvaalen Les Essarts-le-Roi, France
Sauce for thought Why does food taste so much better when you are hungry? My family calls it “hunger sauce”.
n That hunger is the best sauce is proverbial in various languages. But remember that many of our ancestors were intimately familiar with famine. Many locally popular delicacies such as olives, chillies and garlic contain poisons and repellents that are repugnant when unfamiliar. So at first such foods would require a special sauce: presumably ancestors under the temptation
readers in any medium or in any format. New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). To view unanswered questions visit www.newscientist.com/topic/lastword.
of hunger, that greatest of all condiments, were driven to try the new foods in desperation, then learned to like them. One of our most important hunger-associated hormones, ghrelin, influences certain brain regions including the hippocampus, a major centre of learning processes. It seems likely that eating anything that makes a starving belly feel better adds that foodstuff to the mental list of things that don’t taste so bad really – things that when suitably combined with foody tastes and smells, we learn to enjoy. Though repellent when you are sated, they will have you positively slavering when hungry. Some flavourings, such as pepper and mustard, may not satisfy the belly, but they became appetising through association with other satisfying foods, some of which – such as gamey meat – are barely tolerable without them. Jon Richfield Somerset West, South Africa n Never mind the physiological and chemical reasons for food tasting better when hungry, we should not be eating unless we are hungry. Stuffing ourselves with unneeded food will lead to obesity, food wastage and a whole host of other problems. Eat just enough to satisfy your hunger at that point and then wait until really hungry again. The result? Consistently wonderful-tasting food! Gillian Peall Macclesfield, Cheshire, UK
Vineyard to farmyard While perusing the back of a bottle of Australian wine, I noticed that egg and milk were among the ingredients. What are they used for, do they stay in the wine and, most importantly, do they affect the taste?
n Egg white – for its albumen – and milk – for its phosphoprotein casein – are used to clarify wine. The process of removing tannins and proteins to keep wine clear is called fining. Attempts to clarify wine are as old as winemaking. Other traditional agents are isinglass, from the dried swim bladders of fish, and ox blood, horse gelatins, seaweed and clay. As someone called Grapegrower states in the fascinating blog On the Grapevine (bit.ly/L1DCMe), “almost any protein will work to some extent by binding to others and forming the solid deposits”. Those who regard unfined or unfiltered wines as superior to clarified, stabilised ones might want to think again. Like any cloudy “natural” alcohol, they contain a mix of polymerised tannins, phenols, proteins, yeast cells, grape skins and other hangers-on that could give you a hangover. There’s more on fining in Jordan P. Ross’s article “Fining and Filtration: The True Story” (bit.ly/12heiKe). By the way, US navy cooks traditionally cracked a raw egg into brewing coffee to clarify the joe. Toshi Knell Nowra, New South Wales, Australia
Will we ever speak dolphin? The new book out now: packed full of wit, knowledge and extraordinary discovery Available from booksellers and at newscientist.com/dolphins
n I’m a student who has recently developed an obsession with home-brewed beer, so I hope I can offer some insight. Nearly all beer contains hops. This provides the bitter taste and
“UV light causes beer to develop thiols – the sulphur analogue of alcohols – causing a skunky flavour” also acts as a preservative (some natural deodorants even use hops for its antimicrobial action). Hops contain isohumulones, which provide part of the bitter flavour – and this is where the problem with light arises. When UV light hits these compounds they decompose, leading to the creation of free radicals that react with sulphur-containing amino acids. The product is a thiol – the sulphur analogue of alcohols – and this leads to a “skunky” flavour, so called for obvious reasons. To protect against this, manufacturers use brown bottles that block out some of the UV rays. Clear and green bottles offer far less protection and so are more prone to develop a skunky flavour. Try leaving a glass of beer out in the sun for even 10 minutes and
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of answers published in the magazine will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material that has been submitted by
Last words past and present at newscientist.com/topic/lastword
compare it with one not in direct sunlight, and you will get an idea of what skunky beer tastes like. Robert Law Duffield, Derbyshire, UK n Visible and UV light causes a reaction in which riboflavin (vitamin B2) acts as a catalyst to break down bitter compounds called isohumulones that come from hops. This creates free radicals. One of these, 1,1-dimethylallyl, can then take a thiol group from a sulphurcontaining amino acid to become 3-methylbut-2-ene-1-thiol. This compound is similar to two of the sulphurous compounds in a skunk’s spray, namely 2-butene-1thiol and 3-methyl-1-butanethiol. Brown bottles cut out most of the harmful wavelengths of light so beer does not become “skunked”. Eric Kvaalen Les Essarts-le-Roi, France
Sauce for thought Why does food taste so much better when you are hungry? My family calls it “hunger sauce”.
n That hunger is the best sauce is proverbial in various languages. But remember that many of our ancestors were intimately familiar with famine. Many locally popular delicacies such as olives, chillies and garlic contain poisons and repellents that are repugnant when unfamiliar. So at first such foods would require a special sauce: presumably ancestors under the temptation
readers in any medium or in any format. New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). To view unanswered questions visit www.newscientist.com/topic/lastword.
of hunger, that greatest of all condiments, were driven to try the new foods in desperation, then learned to like them. One of our most important hunger-associated hormones, ghrelin, influences certain brain regions including the hippocampus, a major centre of learning processes. It seems likely that eating anything that makes a starving belly feel better adds that foodstuff to the mental list of things that don’t taste so bad really – things that when suitably combined with foody tastes and smells, we learn to enjoy. Though repellent when you are sated, they will have you positively slavering when hungry. Some flavourings, such as pepper and mustard, may not satisfy the belly, but they became appetising through association with other satisfying foods, some of which – such as gamey meat – are barely tolerable without them. Jon Richfield Somerset West, South Africa n Never mind the physiological and chemical reasons for food tasting better when hungry, we should not be eating unless we are hungry. Stuffing ourselves with unneeded food will lead to obesity, food wastage and a whole host of other problems. Eat just enough to satisfy your hunger at that point and then wait until really hungry again. The result? Consistently wonderful-tasting food! Gillian Peall Macclesfield, Cheshire, UK
Vineyard to farmyard While perusing the back of a bottle of Australian wine, I noticed that egg and milk were among the ingredients. What are they used for, do they stay in the wine and, most importantly, do they affect the taste?
n Egg white – for its albumen – and milk – for its phosphoprotein casein – are used to clarify wine. The process of removing tannins and proteins to keep wine clear is called fining. Attempts to clarify wine are as old as winemaking. Other traditional agents are isinglass, from the dried swim bladders of fish, and ox blood, horse gelatins, seaweed and clay. As someone called Grapegrower states in the fascinating blog On the Grapevine (bit.ly/L1DCMe), “almost any protein will work to some extent by binding to others and forming the solid deposits”. Those who regard unfined or unfiltered wines as superior to clarified, stabilised ones might want to think again. Like any cloudy “natural” alcohol, they contain a mix of polymerised tannins, phenols, proteins, yeast cells, grape skins and other hangers-on that could give you a hangover. There’s more on fining in Jordan P. Ross’s article “Fining and Filtration: The True Story” (bit.ly/12heiKe). By the way, US navy cooks traditionally cracked a raw egg into brewing coffee to clarify the joe. Toshi Knell Nowra, New South Wales, Australia
Will we ever speak dolphin? The new book out now: packed full of wit, knowledge and extraordinary discovery Available from booksellers and at newscientist.com/dolphins