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THE LAST WORD Foaming mad I have a handheld milk foamer for my coffee. I can foam milk to twice its volume when it is cold, out of the fridge, but it barely foams at all when heated. Why is that?
n Creating a milk foam depends largely on the protein casein, which stabilises bubbles in the milk. The protein forms particles called micelles and the stronger the structure of these particles, the greater the volume and durability of the foam. Milk also contains many different fats in the form of long fatty acid chains attached to a glycerol backbone. Heating it increases the activity of an enzyme called lipase. This encourages lipolysis, a process by which fats break down into their constituent fatty acids and glycerol. The glycerol and free fatty acids can weaken casein’s structure, causing air bubbles to collapse more easily. If the milk has just been removed from the fridge,
so there are fewer fat breakdown products to weaken the casein. While this should help create a fuller foam, the taste may leave something to be desired. Sam Buckton Hertfordshire, UK
Fluff stuff Why do some woollen cardigans or jerseys produce a lot of pilling, whereas others don’t? Is there any way to know beforehand if a wool garment will be prone to pilling?
the fleece is prepared and spun into wool. Hand spinners typically prepare short-fibred fleece by carding it into rolls of fibre called rolags, then spinning it in a “woollen” style. This causes the fibres to become randomly arranged and the resulting yarn is light and full of air, making it easier for fibres to work to the yarn’s surface. Long-fibred fleece is typically prepared by combing, which removes the shorter fibres. It is then spun in a “worsted” style, which keeps the long fibres parallel and smoothed down, thus making it hard for them to escape the yarn and cause pilling.
its fats are largely intact, so casein is able to stabilise any foam. The freshness of the milk also has an effect on foaming, because the longer the milk is left to stand, the more of its fats will be broken down. To ensure a good froth, it helps to use milk with a low fat content, such as skimmed milk,
n Pilling is caused by short fibres working themselves to the surface of the fabric. There, friction from “A dense fabric holds the whatever the fabric is in contact fibres firmly and has less with causes the scales on each tendency to pill. A loose fibre to lock to those on other one lets them escape” fibres, with the result that they become matted into a ball. There are several contributing factors. The amount of twist in a yarn The first is the nature of the also affects its tendency to pill; fleece. The fleece of some sheep a higher twist holds the fibres breeds, such as Southdown, has more firmly and prevents them short fibres typically between escaping. Many commercial 4 and 6 centimetres long, while knitting yarns are quite lightly long-wool fleece such as spun, with little twist, whereas a Wensleydale can have locks yarn intended for weaving – often up to 30 centimetres. spun from long-wool fleece – will It is easier for a short fibre to usually have a much higher twist. work its way to the surface of a Finally, the way the yarn is fabric than a long one. And some turned into fabric can affect fleeces are easier to felt than pilling. A dense fabric will hold others; Ryeland, with a staple the fibres firmly and have less length of 5 to 6 centimetres, is tendency to pill, while a loose famously difficult to felt while one will allow them to escape. Merino, which has a similar Seeing as the questioner length, felts readily. Loose fibres mentioned woollen fabrics, I have that will not felt cannot form pills. described features of sheep’s wool. A second factor is the way that Other fibres, for example alpaca or
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, 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). Unanswered questions can also be found at this URL.
“Skimmed milk makes a fuller foam, but the taste may leave something to be desired”
synthetic fibres such as acrylic, are not officially called wool but the same principles will apply. To see if a wool garment will be prone to pilling, examine the fabric to see how dense it is and how tightly the yarn is twisted – the looser is it, the more likely it is to pill. Judith Edwards (hand spinner) Cumbria, UK
This week’s questions Upside drone
Why do military drones look so different from military aircraft? For example, their tail fins point downwards. Martin McCann Worcester, UK Clucking on
Why do hens cluck loudly after laying an egg? James Turton Bristol, UK Banding together
Seeing photos of the aurora borealis, which has been visible in the UK recently, I wondered why there are bands of colour. I’m aware that the interaction of ionised particles with different elements creates different colours, but why do they appear in bands? Are there distinct layers of nitrogen, oxygen or other gasses in the upper atmosphere? Derek Woodroffe Stapleford, Nottingham, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything
THE LAST WORD Foaming mad I have a handheld milk foamer for my coffee. I can foam milk to twice its volume when it is cold, out of the fridge, but it barely foams at all when heated. Why is that?
n Creating a milk foam depends largely on the protein casein, which stabilises bubbles in the milk. The protein forms particles called micelles and the stronger the structure of these particles, the greater the volume and durability of the foam. Milk also contains many different fats in the form of long fatty acid chains attached to a glycerol backbone. Heating it increases the activity of an enzyme called lipase. This encourages lipolysis, a process by which fats break down into their constituent fatty acids and glycerol. The glycerol and free fatty acids can weaken casein’s structure, causing air bubbles to collapse more easily. If the milk has just been removed from the fridge,
so there are fewer fat breakdown products to weaken the casein. While this should help create a fuller foam, the taste may leave something to be desired. Sam Buckton Hertfordshire, UK
Fluff stuff Why do some woollen cardigans or jerseys produce a lot of pilling, whereas others don’t? Is there any way to know beforehand if a wool garment will be prone to pilling?
the fleece is prepared and spun into wool. Hand spinners typically prepare short-fibred fleece by carding it into rolls of fibre called rolags, then spinning it in a “woollen” style. This causes the fibres to become randomly arranged and the resulting yarn is light and full of air, making it easier for fibres to work to the yarn’s surface. Long-fibred fleece is typically prepared by combing, which removes the shorter fibres. It is then spun in a “worsted” style, which keeps the long fibres parallel and smoothed down, thus making it hard for them to escape the yarn and cause pilling.
its fats are largely intact, so casein is able to stabilise any foam. The freshness of the milk also has an effect on foaming, because the longer the milk is left to stand, the more of its fats will be broken down. To ensure a good froth, it helps to use milk with a low fat content, such as skimmed milk,
n Pilling is caused by short fibres working themselves to the surface of the fabric. There, friction from “A dense fabric holds the whatever the fabric is in contact fibres firmly and has less with causes the scales on each tendency to pill. A loose fibre to lock to those on other one lets them escape” fibres, with the result that they become matted into a ball. There are several contributing factors. The amount of twist in a yarn The first is the nature of the also affects its tendency to pill; fleece. The fleece of some sheep a higher twist holds the fibres breeds, such as Southdown, has more firmly and prevents them short fibres typically between escaping. Many commercial 4 and 6 centimetres long, while knitting yarns are quite lightly long-wool fleece such as spun, with little twist, whereas a Wensleydale can have locks yarn intended for weaving – often up to 30 centimetres. spun from long-wool fleece – will It is easier for a short fibre to usually have a much higher twist. work its way to the surface of a Finally, the way the yarn is fabric than a long one. And some turned into fabric can affect fleeces are easier to felt than pilling. A dense fabric will hold others; Ryeland, with a staple the fibres firmly and have less length of 5 to 6 centimetres, is tendency to pill, while a loose famously difficult to felt while one will allow them to escape. Merino, which has a similar Seeing as the questioner length, felts readily. Loose fibres mentioned woollen fabrics, I have that will not felt cannot form pills. described features of sheep’s wool. A second factor is the way that Other fibres, for example alpaca or
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, 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). Unanswered questions can also be found at this URL.
“Skimmed milk makes a fuller foam, but the taste may leave something to be desired”
synthetic fibres such as acrylic, are not officially called wool but the same principles will apply. To see if a wool garment will be prone to pilling, examine the fabric to see how dense it is and how tightly the yarn is twisted – the looser is it, the more likely it is to pill. Judith Edwards (hand spinner) Cumbria, UK
This week’s questions Upside drone
Why do military drones look so different from military aircraft? For example, their tail fins point downwards. Martin McCann Worcester, UK Clucking on
Why do hens cluck loudly after laying an egg? James Turton Bristol, UK Banding together
Seeing photos of the aurora borealis, which has been visible in the UK recently, I wondered why there are bands of colour. I’m aware that the interaction of ionised particles with different elements creates different colours, but why do they appear in bands? Are there distinct layers of nitrogen, oxygen or other gasses in the upper atmosphere? Derek Woodroffe Stapleford, Nottingham, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything