Tag Archives: colour

Marvellous Mushroom Science

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Glistening ink caps produce a dark, inky substance.

Yesterday I had the fantastic experience of a “fungi forage” with Dave Winnard from Discover the Wild, organised by Incredible Edible Oxford. There are few nicer things than wandering around beautiful Oxfordshire park- and woodland on a sunny October day, but Dave is also an incredibly knowledgeable guide. I’ve always thought mushrooms and fungi were interesting – living organisms that are neither plants nor animals and which we rely on for everything from antibiotics to soy sauce – but I had lots to learn.

Did you know, for example, that fungi form some of the largest living organisms on our planet? And that without them most of our green plants wouldn’t have evolved and probably wouldn’t be here today?

And from a practical point of view, what about the fact that people once used certain fungi to light fires? I’ve always imagined fungi as being quite wet things with a high water content (unless they’re deliberately dried, of course), but some are naturally very dry. Ötzi, the mummified man thought to have lived between 3400and 3100 BCE, was found with two types of fungus on him: birch fungus, which has antiparasitic properties, and a type of tinder fungus which can be ignited with a single spark and will smolder for days.

Coprine causes unpleasant symptoms, including nausea and vomiting, when consumed with alcohol.

Then, of course, there’s all the interesting chemistry. Early on in the day, we came across some glistening ink caps.The gills of these disintegrate to produce a black, inky liquid which contains a form of melanin and can be used as ink. And there’s more to this story: as I’ve already mentioned, fungi are not plants and they can’t photosynthesise, but it seems that some fungi do use melanin to harness gamma rays as energy for growth. Extra mushrooms for the Hulk’s breakfast, then?

Moving away from pigments for a moment, a related species to the glistening ink cap, the common ink cap, contains a chemical called coprine. This causes lots of unpleasant symptoms if it’s consumed with alcohol, similar to Disulfiram, the drug used to treat alcoholism. For this reason one of this mushroom’s other names is tippler’s bane. The coprine in the mushrooms effectively causes an instant hangover by accelerating the formation of acetaldehyde (also known as ethanal) from alcohol. Definitely don’t pair that mushroom omelette with a nice bottle of red and, worse, you’ll need to stay off the booze for a while: apparently the effects can linger for a full three days.

Yellow stainer mushrooms look like field mushrooms, but are poisonous.

We also came across some yellow stainer mushrooms. These look a lot like field mushrooms, but be careful – they aren’t edible. They cause nasty gastric sympoms and are reportedly responsible for most cases of mushroom poisoning in this country, although some people seem to be able to eat them without ill effect. They had a slightly chemically scent that reminded me “new trainer” smell – sort of rubbery and plasticky. It’s often described as phenolic, but I have to say I didn’t detect that myself – although yellow stainers have been shown to contain phenol and this could account for their poisonous nature. Anyway, it was an aroma that wouldn’t be entirely unpleasant if I were opening a new shoebox, but it wasn’t something I’d really want to eat. Apparently the smell gets stronger as you cook them, so don’t ignore what your nose is telling you if you think you have a nice pan of field mushrooms.

4,4′-Dimethoxyazobenzene is an azo dye.

The real giveaway with yellow stainers, though, is their tendency to turn yellow when bruised or scratched, hence the name. This, it seems, is due to 4,4′-dimethoxyazobenzene. The name might not be familiar, but A-level Chemistry students will recognise the structure: it’s an azo-dye. Quite apart from being a very useful word in Scrabble, azo compounds are well-known for their characteristic orange/yellow colours. It’s not really clear whether it forms in the mushroom due to some sort of oxidation reaction, or whether it’s in the cells anyway but only becomes visible when the cells are damaged. Either way, it’s something to look out for if you spot a patch of what look like field mushrooms.

The blushing wood mushroom.

We also came across several species which are safe to eat. One I might look out for in future is the blushing wood mushroom. As is often the way with fungi, the name is literal rather than merely poetic. These mushrooms have a light brown cap, beige gills, and a pale stem, but they turn bright red when cut or scratched due to the formation of an ortho-quinone. It’s quite a dramatic colour-change, and makes them pretty easy to identify. Apparently they’re normally uncommon here, but we found quite a lot of them, which might be something to do with this year’s unusally hot and dry summer.

Red ortho-quinone causes blushing wood mushrooms to literally blush.

I tried to find out the reasons for these colour-changes. In the plant and animal kingdoms pigments are usually there for good reason: camouflage, signalling and communication or, as with chlorophyll, as a way of making other substances. Fruits, for example, often turn bright red as they ripen because it makes them stand out from the green foilage and encourages animals to eat them so that the seeds can be spread. Likewise, they’re green when they’re unripe because it makes them less obvious and less appealing. But what’s the advantage for the mushroom to change colour once it’s already damaged? Perhaps there isn’t one, and it’s just an accident of their biology, but if so it seems strange that it’s a feature of several species. I couldn’t find the answer; if any mycologists are reading this and know, get in touch!

Velvet shank mushrooms.

Other edible species we met were fairy ring champignons, field blewits and jelly ear fungus – which literally looks like a sort of transparent ear. I’ll definitely be looking out for all of these in the future, but it’s important to watch out for dangerous lookalikes. Funeral bell mushrooms, for example, look like the velvet shank mushrooms we found but, once again, the name is quite literal – funeral bells contain amatoxins and eating them can cause kidney and liver failure. As Dave was keen to remind us: never eat anything you can’t confidently name!

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In the fridge or on the windowsill: where’s the best place to keep tomatoes?

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Fresh fruit and vegetables are great, but where’s the best place to store them?

I’ve mentioned before that my Dad is a professional plant-wrangler (if you’ve never read the electric daisies post, do go and have a look – it’s a little-read favourite) and he often brings me home-grown fruit and vegetables.

What follows is an inevitable disagreement about storage, specifically, my habit of putting everything in the fridge.

In my defence, modern houses rarely have pantries (boo) and we don’t even have a garage. We do have a shed, but it’s at the bottom of our poorly-lit, somewhat muddy garden. Do I want to traipse out there on a cold, dark, autumn evening? No, I do not. So the fabled “cool, dark place” is a bit of problem. My fridge is cool and dark, I have argued, but here’s the thing – turns out, it’s too cool. And quite probably too dark.

This I have learned from the botanist James Wong (@botanygeek on Twitter), whose talk I attended on Monday this week at the Mathematical Institute in Oxford. James, it turns out, had a rather similar argument with his Mum, particularly regarding tomatoes.

We should’ve listened to out parents, because they were right. A lot of fruit and vegetables really are better stored outside of the fridge, and for tomatoes in particular “better” actually means “more nutritious”.

Lycopene is a very long molecule with lots of double C=C bonds.

Tomatoes, James explained, contain a lot of a chemical called lycopene. It’s a carotene pigment, and it’s what gives tomatoes their red colour.

Lycopene has lots of double bonds between its carbon atoms which form something chemists call a conjugated system. This has some rather cool properties, one of which is an ability to absorb certain wavelengths of light. Lycopene is especially good at absorbing blue and green wavelengths, leaving our eyes to detect the red light that’s left.

Lycopene absorbs blue and green light, which is why tomatoes appear red.

Tomatoes and lycopene also seem to have a lot of health benefits. There’s some evidence that lycopene might reduce the risk of prostate and other cancers. It also appears to reduce the risk of stroke, and eating tomato concentrate might even help to protect your skin from sun damage (don’t get any ideas, you still need sunblock). Admittedly the evidence is currently a bit shaky – it’s a case of “more research is needed” – but even if it turns out to that the causative relationship isn’t terribly strong, tomatoes are still a really good source of fibre and vitamins A, C and E. Plus, you know, they taste yummy!

But back to the fridge. Surely they will keep longer in the fridge, and the low temperatures will help to preserve the nutrients? Isn’t that how it works?

Well, no. As James explained, once tomatoes are severed from the plant they have exactly one purpose: to get eaten. The reason, from the plant’s point of view, is that the critter which eats them will hopefully wander off and – ahem – eliminate the tomato seeds at a later time, somewhere away from the parent plant. This spreads the seeds far and wide, allowing little baby tomato plants to grow in a nice, open space with lots of water and sun.

For this reason once the tomato fruit falls, or is cut, from the tomato plant it doesn’t just sit there doing nothing. No, it carries on producing lycopene. Or rather, it does if the temperature is above about 10 oC. Below that temperature (as in a fridge), everything more or less stops. But, leave a tomato at room temperature and lycopene levels increase significantly. Plus, the tomato pumps out extra volatile compounds – both as an insect repellant and to attract animals which might usefully eat it – which means… yes: room temperature tomatoes really do smell better. As if that weren’t enough, chilling tomatoes can damage cell membranes, which can actually cause them to spoil more quickly.

In summary, not only will tomatoes last longer out of the fridge, they will actually contain more healthy lycopene!

Anecdotally, once I got over my scepticism and actually started leaving my tomatoes on my windowsill (after years of refrigeration) I discovered that it’s true. My windowsill tomatoes really do seem to last longer than they used to in the fridge, and they almost never go mouldy. Of course, it’s possible that I might not be comparing like for like (who knows what variety of tomato I bought last year compared to this week), but I urge you to try it for yourself.

James mentioned lots of other interesting bits and pieces in his talk. Did you know that sun-dried shiitake mushrooms are much higher in vitamin D? Or that you can double the amount of flavonoid you absorb from your blueberries by cooking them? (Take that, raw food people!) Storing apples on your windowsill is likely to increase the amount of healthy polyphenols in their skin, red peppers are better for you than green ones, adding mustard to cooked broccoli makes it more nutritious, and it would be much better if we bought our butternut squash in the autumn and saved it for Christmas – it becomes sweeter and more flavoursome over time.

In short, fascinating. Who wants to listen to some “clean eater” making it up as they go along when you can listen to a fully-qualified botanist who really knows what he’s talking about? Do check out the book, How to Eat Better, by James Wong – it’s packed full of brilliant tidbits like this and has loads of recipes.

And yes, Dad: you were right.

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Five science facts we learned at school?

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This week a post called ‘Five Science ‘Facts’ We Learnt At School That Are Plain Wrong‘ popped into my Facebook feed from a few different sources.

It led to more than one argument, and the unearthing of some interesting titbits. Most of these facts aren’t directly about chemistry, but hey, still interesting. Let’s have a look:

We’re taught we only have five senses: smell, sight, hearing, touch and taste
True enough that there are more than five, but I clearly remember being told in school that balance and pain were also senses, so I’m fairly sure biology teachers have been quietly trying to dispel this one for decades.

plastic paperclips

Non-magnetic paper-clips. Ha!

Which of the following are magnetic: a tomato, you, paper-clips? (Answer: all of the above)
I think this is a misleading question. What do you mean when you say ‘magnetic’? I think most people understand that to mean something that’s capable of being magnetised or at least is attracted to your everyday fridge magnet. In other words, the ferromagnetic materials: iron, nickel, cobalt and most of their alloys. True enough tomatoes and people interact with magnetic fields (this is the basis behind MRI scanners – check out these beautiful images) but does that make them magnetic? We-ell….technically…. (there are lots of types of magnetism) but it seems a bit mean to criticise an assumption by asking a less-than-clear question about it. Besides, if you’re going to be pedantic about it, what’s that paper-clip made of hmm? Plastic and aluminium (both generally considered to be completely non-magnetic) paper-clips exist. Bad question. Next!

CMYKThe true primary colours for paints and pigments are cyan, magenta and yellow
Broadly fair enough, look at your printer cartridge. Although we really ought to include black as well (which the original article didn’t mention; it’s the K in the CMYK model). You can make something pretty close to black by mixing the others, but it’s not the nice, crisp, blackest black that people want for text and outlines. All that said, to actually get red from a mixture of magenta and yellow you have to have pretty pure pigments. Grab a paint box and try mixing something that looks like magenta with something that looks like yellow, and you’ll actually get something that looks like orangey-pink (serious artists agree that if you want really bright red, you’re better off just buying some red pigment). Whereas if you mix blue paint with yellow paint you will, fairly reliably, get green of one shade or another. I just worry that attempting to clear this one up is going to cause a lot of children to mess up their paintings. That’s all I’m saying.

A little addition here: this question then led to a debate about the colour spectrum of visible light. How many colours are there, exactly? It’s commonly held that Newton invented the colour indigo because he felt, possibly for superstitious reasons, that there ought to be seven colours. As a result, some people will tell you the spectrum actually consists of six colours rather than seven: red, orange, yellow, green, blue and violet. But hang on. Look at a spectrum (here’s one):

600px-Spectrum

What’s that colour in between blue and green there? You might say turquoise, but in a return to the original question it’s more accurately named cyan. That band is pretty obvious. I’d argue that if you’re going to include orange in the spectrum, then you ought to include cyan. And, in fact, some people think that’s exactly what Newton was doing. Except he didn’t call it cyan, he simply called it blue. The bit we think of as blue is what he named indigo. In other words, the spectrum is, in fact: red, orange, yellow, green, cyan, blue, violet. Still seven colours, they just don’t quite fit with the whole Richard Of York Gave Battle In Vain thing.

Of course, those of us in the know are aware that there are actually eight colours. But you need to have octagonal cells in your eyes to see the other one. Or be a cat.

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Debunked in 1974. Still hanging around like a bad smell or, er, taste.

Tongue taste maps are nonsense
Yep. This one is unambiguous: there aren’t regions for sweet, salt, bitter etc. on your tongue. This was debunked back in 1974, but it’s still hanging around for some reason.

There are more states of matter than just solid, liquid and gas
Ah-ha, a chemistry one! Again, this is true. The strict states of solid, liquid and gas are fine when you’re talking about elements and pure, fairly simple, compounds (water, for example), but matter can indeed take other forms. There are ‘liquid crystals‘ – you’re probably reading this right now using some – and yes, there’s plasma. Once you get into mixtures all bets are off (no, you can’t melt wood, sorry). And colloids are a whole other kettle of fish.

But I think this is one of those times where you have to ask yourself why are we bothering to talk about solids, liquids and gases in the first place? Is it purely so that students can memorise three words? No. It’s so that they can go on to understand the concepts of melting and boiling, and their partners freezing and condensing. These ideas are critical to understanding ideas of measuring temperature as solid liquid gaswell as what happens to particles when they warm up (or cool down). Adding other technical terms in at this early stage is just likely to cause confusion. I don’t think that learning about the transition from solid to liquid to gas precludes later learning about liquid crystals, colloids and the like (hey, it’s how I did it). You’re just adding more information to a simple model, and someone studying A-level sciences and beyond ought to be capable of dealing with that. No harm, no foul, I say.

So there we have it: less “Five Science ‘Facts’ We Learnt At School That Are Plain Wrong”, and more one thing your teacher probably tried to correct you on, one misleading question, one thing you might have learned incorrectly at school, and a couple that might be technically untrue but it doesn’t really matter that much in the long run. But I suppose that IS less of a snappy title for an article.

Truth, Justice, Freedom, Reasonably Priced Love, and a Hard-Boiled Egg.