ÐÓ°ÉÔ­´´

Strings attached

Question: Why does grilled cheese go stringy?

Answer: The uncooked cheese contains long-chain protein molecules more or less curled up in a fatty, watery mess. When you heat cheese, the fats and proteins melt and if you fiddle with the fluid, the chains can get dragged into strings. Grab a bit of the molten cheese and pull, and you get a filament, in much the same way that you can draw and twist cotton wool into yarn.

You can do similar things with polythene from plastic bags by heating or stretching the plastic to curl or stretch the long-chain molecules. When the molecules are curled up, the plastic is softish and waxy. When they are stretched into fibres, the result is elastic and strong in the direction of the stretch, although it splits easily between the chains lying along the fibre.

Jon Richfield

Dennesig, South Africa

Answer: As the cheese melts, the long-chain protein molecules bind together to form fibres in the liquid mass of melted cheese. I believe that this characteristic can actually be used to measure the protein content of a cheese sample directly. A string of cheese is pulled away from the sample, and the distance to which the fibre will extend away from its attachment point on the main piece of cheese is measured against some reference sample of known protein content.

Mike Perkin

by e-mail, no address supplied

What’s up doc?

Question: Why are carrots orange? It is difficult to understand how the high levels of subterranean betacarotene could have a role in harvesting light energy. Or is this vegetable a result of the plant breeder’s art?

Answer: Not all carrots are orange. There is a huge range of colours, from an almost black purple, through red, orange, yellow and white. All have been selected by generations of gardeners and, more recently, plant breeders.

You can blame our boring suppliers for the restricted range in the shops. The wild form is white, and that colour is dominant in most types. This is fortunate because carrots are prone to crossing by mistake and white roots indicate something has gone wrong.

Jeremy Cherfas

Somerset

It’s Frothy man

Question: What causes the froth on a good cup of espresso and why is it sensitive to the conditions under which the water is added to the coffee?

Answer: The brownish froth on true espresso coffee is actually caramel. The high temperature and pressure in an espresso machine caramelises sugar in the coffee. The aerated caramel is expelled with the espresso. Too low a temperature or pressure or an old and dirty coffee chamber all stop this process.

Peter Lange

by e-mail, no address supplied

Klingoff

Question: Why doesn’t cling film cling to a metal bowl as well as it does to an equally smooth glass or ceramic one?

Answer: Cling film, known as cling wrap in the US, works because it acquires an electric charge as it is peeled from the roll. It can then stick to an insulating body by the same mechanism that an uncharged piece of paper sticks to the charged glass of your computer or television screen.

The mechanism relies upon the cling film and the object to which it is sticking being at a substantially different electrical potential. This works when the object is an insulator. When the object is metal, the charge on the film is dissipated throughout the object, so negating the effect.

Old cling film taken off the roll doesn’t work either. After a while, the charge breaks away, and the clingyness is lost.

Alistair Hamilton

by e-mail, no address supplied

Answer: Cling film becomes charged with static electricity as it peels from the roll. You can sense the charge by peeling some off and holding it near your face—you will feel the hairs on your cheek stand up. Metal drains away static—glass (or plastic) retains static on its surface. The more static, the greater the cling.

Jeffrey Wells

by e-mail, no address supplied

Herding instinct

Question: If I put a duvet cover in my washing machine with a full load of numerous smaller items of clothing, the latter frequently end up together inside a corner of the closed end of the duvet cover, even though I always put them into the machine separately. The detergent dispenser ball often ends up inside it as well. Can anyone explain how this can happen inside the confined space of the washing machine drum?

Answer: Duvet covers are commonly made of a cotton/polyester cloth printed on one side (the right side), with the other side (the wrong side) having less dye on it. Generally the wrong side is softer and has lower friction than the printed side. If the cover is put in the washing machine with the right side outwards it turns itself inside out during the wash cycles, possibly due to the relative frictional difference between its two sides.

Small objects such as socks and undergarments get caught up in this inversion and end up inside the inverted duvet cover. The wash and spin cycles that follow push the objects deeper into the cover. Larger printed pillow cases show the same effect. Experiments show that the inversion does not take place if the cover is turned inside out (wrong side showing) before putting it in the washing machine.

Z. Tahir

by e-mail, no address supplied

Answer: This is actually a very good illustration of a stochastic process. It is analogous to a drunk walking along a path bounded by a wall and a ditch. The drunk’s lurches are random—either into the wall or the ditch. The drunk will bounce off the wall and back onto the path. But having fallen into the ditch, the drunk will stay there.

So it is with your detergent dispenser ball. It wanders around inside the machine randomly but is caught in the duvet corner because once inside it can’t easily get out. It always happens to mine as well.

David Byrne

Durham

Extensive research in the New ÐÓ°ÉÔ­´´ laundrette shows that while duvet inversion can take place, pure cotton pillowcases also swallow socks stochastically. Depending on the composition of your laundry, either or both effects may operate—Ed

Food scare

Question: Why are you not supposed to refreeze meat which has defrosted? At what stage of defrosting does it become unsafe to refreeze the meat?

Answer: Freezing food does not kill most bacteria and other nasties. It merely slows down their metabolic rate, and they enter a kind of suspended animation.

On defrosting, these nasties all wake up and start to reproduce. If the food is consumed immediately there should only be a relatively low dose of nasties. However, if the food is refrozen, all the new baby nasties are also put into suspended animation.

When the food is defrosted the reproduction begins again with a higher starting population, resulting in a bigger final population—much more likely to cause illness.

Simon Scarle

London

Answer: You shouldn’t refreeze meat because its cell structure is heavily damaged by expanding water crystals. Freezing it twice doubles the damage making it quite unappetizing.

Tom Boward

by e-mail, no address supplied