杏吧原创

Blooming fruit

Question: Can somebody tell me what the bloom is on the skins of fruit such
as plums and grapes? How does it get there and what does it do?

Answer: The delicate powdery surface deposit, or bloom, that can be seen on
these fruit is formed by many similar varieties of wild yeast. Like all yeasts
and other organisms, they multiply by using sugars and nutrients in fruit as an
energy source. As far as humankind is concerned, their most important property
is that some of the wild yeasts are used to ferment sugar in fruit to make wine
or beer. This is a by-product of their metabolism in as much as they excrete
carbon dioxide and alcohol. So the phrase 鈥渁 night out on the piss鈥� is very apt
really.

Neil Donaldson

Telford

Forest of fear

Question: I read recently that oak and fir trees are far more likely to be
struck by lightning than pines, and beech is the tree least likely to attract a
lightning strike. Does anybody know if this is correct and, if so, why?

Answer: Almost a century ago, a monthly journal Country Queries and
Notes was first published. This question was raised in its first issue and
attracted an enormous amount of interest from readers. Their responses were
still arriving a year later.

Replies were compiled from many different sources and showed the following
number of lightning strikes: oak 484, poplar 284, willow 87, elm 66, pine 54,
yew 50, beech 39, ash 33, pear 30, walnut 22, lime 16, cherry 12, chestnut 11,
larch 11, maple 11, birch 9, apple 7, alder 6, mountain ash 2 and hawthorn 1.
Only after further prompting from the editor did one reader admit to seeing a
stricken sycamore. There were assertions that holly was never seen to be
hit.

With no indication of the relative proportions of the trees present the list
may appear meaningless, but it does look as if height has more relevance than
species. Arguments grew a little wearisome but there was some support for the
view that trees with corrugated bark (and therefore traces of moisture)
attracted more strikes than those with smooth bark.

It seems fairly clear, though, that it is best to assume what we all know
already鈥攍ightning can strike anywhere.

James O鈥橦agan

Edinburgh

Answer: The Forestry Commission鈥檚 most recent research paper on the subject
states that oak, poplar and Scots pine are the tree species most frequently
damaged, with beech least likely to be damaged. However, this is based on two
surveys, each with relatively few records. The first was carried out between
1932 and 1935 and the second between 1967 and 1985 and there are some
discrepancies, partly because the earlier survey included only obviously
lightning-damaged trees, while the later one includes non-catastrophic damage,
which is quite common and sometimes barely detectable.

North American publications also show beech, birch and horse chestnut as
relatively unlikely to be struck, compared with oaks, pines and spruces, among
others. North America gets much more lightning than Britain and it is not
uncommon for particularly valuable specimens to be fitted with lightning
conductors in order to preserve them. To my knowledge a conductor has only once
been fitted to a British tree, a particularly large cedar that was considered
especially at risk.

Various theories have been advanced as to why some species are apparently
struck more often, including the possibility that some conduct electricity
better, either through the sap or because their rough bark retains more
rainwater. This would explain why beech, with its smooth bark, is less
susceptible to strikes.

Simon Pryce

Warminster, Wiltshire

This week鈥檚 questions

Salt removal: I have a survival handbook which explains that in the Arctic it
is possible to obtain fresh water from sea ice, even though seawater is itself
undrinkable. The trick is to cut blocks of sea ice and then leave them stacked.
After a while, the top layer of ice becomes free from salt. Is this true and if
so, what is the underlying mechanism?

Billy Sturrock

Birmingham

Atomic mushrooms: This summer our high school visited the museum in Hiroshima
about the American attack on Japan with an atomic bomb. We also heard stories
from survivors and saw pictures of the destruction, some taken from a long way
away showing a strange giant black cloud over Hiroshima. I wondered why the
nuclear bomb always makes a mushroom-shaped cloud?

Hiroko Watanabe

Minato-ku, Tokyo

Heated hop: I was sitting with a group of friends in the pub last night and,
as we contemplated our pints of bitter, we wondered why does beer go flat when
it gets warm? Not only that, but the effect seems more pronounced with lager
than with bitter.

Jon Shaw

Brighouse, West Yorkshire

Old odour: Last night my father pulled out all his old copies of New
杏吧原创 to show us that it really has been in existence since the 1950s.
However, we both noticed that the older the magazine, the more musty it smelt.
What is it that creates the distinctive smell of old magazines and books and is
there any way to counteract it?

Paula Drake

St Ives, Cornwall