Onerous ovens: why is cleaning the cooker such a chore?

As I write Thanksgiving was a few days ago, when most Americans traditionally cook a very large meal based around roasted turkey. Most Brits – and other countries of course – have the same thing coming up soon in the form of Christmas, and there are lots of other celebrations around this time of year that seem to feature cooking and food quite heavily.

Whatever your traditions, then, it’s a time when many of us frown critically at the dark, sticky depths of our oven and wonder if, perhaps, we should attempt to give it a clean. Or at least pay someone else to come and clean it.

Why is oven cleaning such a difficult and unpleasant job, anyway? It’s not that hard to clean other surfaces, is it? Why are ovens so particularly awful?

Well, to explain this, we first need to understand fats.

Fats vaporise during cooking.

Most of the grime in your oven is fat, combined with the carbonised remains of… something or other. The sorts of fats that are common in animal and plant products have boiling points around the 300 oC mark (animal fats typically having higher values than plant oils), but they start to form vapours at much lower temperatures, and certainly at typical cooking temperatures there’s plenty vaporised oil around. Besides, under typical conditions most oils will “smoke” – i.e. start to burn – long before they get close to boiling.

We’re all familiar with the idea that fats don’t mix well with water, and herein lies the problem: all that fatty gloop that’s stuck to the inside of your oven just doesn’t want to come off with standard cleaning methods, particularly when it’s built up over time.

Can chemistry help us here? What are fats, chemically? Well, they’re esters. Which may or may not mean anything to you, depending on how much chemistry you can remember from school. But even if you don’t remember the name, trust me, you know the smell. In particular, nail polishes and nail polish removers contain the simple ester known as ethyl acetate, otherwise known as ethyl ethanoate. (Some people say this chemical smells like pear drops which… only really helps if you know what pear drops smell like. Look, it smells of nail polish, okay?)

Fats are esters (image source)

Anyway, the point is that esters have a particular sequence of atoms that has a carbon bonded to an oxygen, which is bonded to another carbon, which is in turn double-bonded to oxygen. This is a bit of a mouthful, so chemists often write it as COOC. In the diagram here, oxygen atoms are red while carbon atoms are black.

There are actually three ester groups in fat molecules – which explains why fats are also known as triglycerides.

In terms of general chemistry, esters form when a carboxylic acid (a molecule which contains a COOH group) reacts with an alcohol (a molecule that contains an OH group). And this is where it all starts to come together – honest – because you’ve probably heard of fatty acids, right? If nothing else, the words turn up in certain food additive names, in particular E471 mono- and diglycerides of fatty acids, which is really common in lots of foods, from ice cream to bread rolls.

Glycerol is a polyol — a molecule that contains several alcohol groups (image source)

Well, this reaction is reversible, and as a result fats (which are esters, remember) break up into fatty acids and glycerol – which is a polyol, that is, a molecule with several alcohol groups. Or, to look at it the other way around: fats are made by combining fatty acids with glycerol.

And the reason it’s useful to understand all this is that the way you break up esters, and therefore fat, is with alkalis. (Well, you can do it with acid, too, but let’s not worry about that for now.)

Strong alkalis break up fats in a chemical reaction called hydrolysis — the word comes from the Greek for water (hydro) and unbind (lysis) and so literally means “split up with water”. Humans have known about this particular bit of chemistry for a long time, because it’s fundamental to making soap. As I said a few months ago when I was banging on about hand-washing, the ancient Babylonians were making soap some 4800 years ago, by boiling fats with ashes – which works because alkaline compounds of calcium and potassium form when wood is burnt at high temperatures.

The grime in ovens is mostly fat.

The really clever thing about all this is that two things are happening when we mix alkali with fat: not only are we breaking up the fat molecules, but also the substances they break up into are water-soluble (whereas fats, as I said at the start, aren’t). Which makes them much easier to clean away with water. Obviously this is the very point of soap, but it’s also handy when trying to get all that baked-on gunk off your oven walls.

Now, in theory, this means you could get some lye (aka sodium hydroxide, probably), smear it all over your oven and voilà. But I don’t recommend it, for a few reasons. Firstly, it’s going to be difficult to apply, since sodium hydroxide is mostly sold as pellets or flakes (it’s pretty easy to buy, because people use it to make soap).

Sodium hydroxide, sometimes called lye, is often sold in the form of pellets.

But, you say, couldn’t I just dissolve it in water and spray or spread it on? Yes, yes you could. But it gets really, really hot when you mix it with water. So you need to be incredibly careful. Because, and this is my next point, chemically your skin is basically fat and protein, and this reaction we’re trying to do on oven sludge works equally well on your skin. Only, you know, more painfully, and with scarring and stuff. In short, if you’re handing lye, wear good nitrile on vinyl gloves and eye protection.

Actually, regardless of how you’re cleaning your oven you should wear gloves and eye protection, because the chemicals are still designed to break down fats and so… all of the above applies. It’s just that specially-designed oven cleaners tend to come with easier (and safer) ways to apply them. For example, they might come as a gel which you can paint on, and/or with bags that you can put the racks into, and may also be sold with gloves and arm protectors (but rarely goggles – get some separately). They might also have an extra surfactant, such as sodium laureth sulfate, added to help with breaking down grease. The main ingredient is still either potassium hydroxide or sodium hydroxide, though.

Well, possibly, but also not really, if you’re sensible.

As an aside, it makes me smile when I come across an article like this which talks about the “serious” chemicals in oven cleaners and more “natural” ways to clean your oven. The “natural” ways are invariably weak acids or alkalis such as lemon juice or baking soda, respectively. They’re essentially ineffective ways of trying to do exactly the same chemistry.

And okay, sure, the gel and the bag and so on in the modern kits are newer tech, but the strong alkali? Nothing more natural than that. As I said at the start, humans have literally been using it for thousands of years.

A point which really cannot be repeated enough: natural does not mean safe.

Fumes can be irritating to skin, eyes and lungs.

Speaking of which, you will get fumes during oven cleaning. Depending on the exact cleaning mixture involved, these will probably be an alkaline vapour, basically (haha) forming as everything gets hot. Such vapour is potentially irritating to skin, eyes and lungs, but not actually deadly toxic. Not that I recommend you stick your head in your freshly-scrubbed oven and inhale deeply, but you take my point. It might give food a soapy, possibly bitter (contrary to what’s stated in some text books, not all alkalis taste bitter, but do not experiment with this) taste if you really over-do it.

In short, if you’re cleaning your oven yourself: follow the manufacturer’s instructions, make sure your kitchen is well-ventilated, leave the oven door open for a while after you’ve finished and, to be really sure, give all the surfaces an extra wash down with plenty of water.

Put the cleaning off until January – after all, the oven’s only going to get dirty again.

And that’s… it, really. Whether you’re cleaning your own oven or getting someone else to do it for you, the chemistry involved is really, really old. And yes, the chemicals involved are hazardous, but not because they’re not “natural”. Quite the opposite.

Or you could just leave it. I mean, it’s only going to get dirty again when you cook Christmas dinner, right?

If you’re studying chemistry, have you got your Pocket Chemist yet? Why not grab one? It’s a hugely useful tool, and by buying one you’ll be supporting this site – it’s win-win! If you happen to know a chemist, it would make a brilliant stocking-filler! As would a set of chemistry word magnets!

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Want something non-sciency to distract you from, well, everything? Why not check out my fiction blog: the fiction phial.

Cleaning chemistry – the awesome power of soap

Well, times are interesting at the moment, aren’t they? I’m not going to talk (much) about The Virus (there’s gonna be a movie, mark my words), because everyone else is, and I’m not an epidemiologist, virologist or an immunologist or, in fact, in any way remotely qualified. I am personally of the opinion that it’s not even especially helpful to talk about possibly-relevant drugs at the moment, given that we don’t know enough about possible negative interactions, and we don’t have reliable data about the older medicines being touted.

In short, I think it’s best I shut up and leave the medical side to the experts. But! I DO know about something relevant. What’s that, I hear you ask? Well, it’s… soap! But wait, before you start yawning, soap is amazing. It is fascinating. It both literally and figuratively links loads of bits of cool chemistry with loads of other bits of cool chemistry. Stay with me, and I’ll explain.

First up, some history (also not a historian, but that crowd is cool, they’ll forgive me) soap is old. Really, really, old. Archaeological evidence suggests ancient Babylonians were making soap around 4800 years ago – probably not for personal hygiene, but rather, mainly, to clean cooking pots. It was originally made from fats boiled with ashes, and the theory generally goes that the discovery was a happy accident: ashes left from cooking fires made it much easier to clean pots and, some experimenting later, we arrived at something we might cautiously recognise today as soap.

Soap was first used to clean pots.

The reason this works is that ashes are alkaline. In fact, the very word “alkali” is derived from the Arabic al qalīy, meaning calcined ashes. This is because plants, and especially wood, aren’t just made up of carbon and hydrogen. Potassium and calcium play important roles in tree and plant metabolism, and as a result both are found in moderately significant quantities in wood. When that wood is burnt at high temperatures, alkaline compounds of potassium and calcium form. If the temperature gets high enough, calcium oxide (lime) forms, which is even more alkaline.

You may, in fact, have heard the term potash. This usually refers to salts that contain potassium in a water-soluble form. Potash was first made by taking plant ashes and soaking them in water in a pot, hence, “pot ash”. And, guess where we get the word potassium from? Yep. The pure element, being very reactive, wasn’t discovered until 1870, thousands of years after people first discovered how useful its compounds could be. And, AND, why does the element potassium have the symbol K? It comes from kali, the root of the word alkali.

See what I mean about connections?

butyl ethanoate butyl ethanoate

Why is the fact that the ashes are alkaline relevant? Well, to answer that we need to think about fats. Chemically, fats are esters. Esters are chains of hydrogen and carbon that have, somewhere within them, a cheeky pair of oxygen atoms. Like this (oxygen atoms are shown red):

Now, this is a picture of butyl ethanoate (aka butyl acetate – smells of apples, by the way) and is a short-ish example of an ester. Fats generally contain much longer chains, and there are three of those chains, and the oxygen bit is stuck to a glycerol backbone.

Thus, the thick, oily, greasy stuff that you think of as fat is a triglyceride: an ester made up of three fatty acid molecules and glycerol (aka glycerine, yup, same stuff in baking). But it’s the ester bit we want to focus on for now, because esters react with alkalis (and acids, for that matter) in a process called hydrolysis.

Fats are esters. Three fatty acid chains are attached to a glycerol “backbone”.

The clue here is in the name – “hydro” suggesting water – because what happens is that the ester splits where those (red) oxygens are. On one side of that split, the COO group of atoms gains a metal ion (or a hydrogen, if the reaction was carried out under acidic conditions), while the other chunk of the molecule ends up with an OH on the end. We now have a carboxylate salt (or a carboxylic acid) and an alcohol. Effectively, we’ve split the molecule into two pieces and tidied up the ends with atoms from water.

Still with me? This is where it gets clever. Having mixed our fat with alkali and split our fat molecules up, we have two things: fatty acid salts (hydrocarbon chains with, e.g. COONa+ on the end) and glycerol. Glycerol is extremely useful stuff (and, funnily enough, antiviral) but we’ll put that aside for the moment, because it’s the other part that’s really interesting.

What we’ve done here is produce a molecule that has a polar end (the charged bit, e.g. COONa+) and a non-polar end (the long chain of Cs and Hs). Here’s the thing: polar substances tend to only mix with other polar substances, while non-polar substances only mix with other non-polar substances.

You may be thinking this is getting technical, but honestly, it’s not. I guarantee you’ve experienced this: think, for example, what happens if you make a salad dressing with oil and vinegar (which is mostly water). The non-polar oil floats on top of the polar water and the two won’t stay mixed. Even if you give them a really good shake, they separate out after a few minutes.

The dark blue oily layer in this makeup remover doesn’t mix with the watery colourless layer.

There are even toiletries based around this principle. This is an eye and lip makeup remover designed to remove water-resistant mascara and long-stay lipstick. It has an oily layer and a water-based layer. To use it, you give the container a good shake and use it immediately. The oil in the mixture removes any oil-based makeup, while the water part removes anything water-based. If you leave the bottle for a minute or two, it settles back into two layers.

But when we broke up our fat molecules, we formed a molecule which can combine with both types of substance. One end will mix with oily substances, and the other end mixes with water. Imagine it as a sort of bridge, joining two things that otherwise would never be connected (see, literal connections!)

There are a few different names for this type of molecule. When we’re talking about food, we usually use “emulsifier” – a term you’ll have seen on food ingredients lists. The best-known example is probably lecithin, which is found in egg yolks. Lecithin is the reason mayonnaise is the way it is – it allows oil and water to combine to give a nice, creamy product that stays mixed, even if it’s left on a shelf for months.

When we’re talking about soaps and detergents, we call these joiny-up molecules “surfactants“. You’re less likely to have seen that exact term on cosmetic ingredients lists, but you will (if you’ve looked) almost certainly have seen one of the most common examples, which is sodium laureth sulfate (or sodium lauryl sulfate), because it turns up everywhere: in liquid soap, bubble bath, shampoo and even toothpaste.

I won’t get into the chemical makeup of sodium laureth sulfate, as it’s a bit different. I’m going to stick to good old soap bars. A common surfactant molecule that you’ll find in those is sodium stearate, which is just like the examples I was talking about earlier: a long hydrocarbon chain with COONa+ stuck on the end. The hydrocarbon end, or “tail”, is hydrophobic (“water-hating”), and only mixes with oily substances. The COONa+ end, or “head”, is hydrophilic (“water loving”) and only mixes with watery substances.

Bars of soap contain sodium stearate.

This is perfect because dirt is usually oily, or is trapped in oil. Soap allows that oil to mix with the water you’re using to wash, so that both the oil, and anything else it might be harbouring, can be washed away.

Which brings us back to the wretched virus. Sars-CoV-2 has a lipid bilayer, that is, a membrane made of two layers of lipid (fatty) molecules. Virus particles stick to our skin and, because of that membrane, water alone does a really bad job of removing them. However, the water-hating tail ends of surfacant molecules are attracted to the virus’s outer fatty surface, while the water-loving head ends are attracted to the water that’s, say, falling out of your tap. Basically, soap causes the virus’s membrane to dissolve, and it falls apart and is destroyed. Victory is ours – hurrah!

Hand sanitisers also destroy viruses. Check out this excellent Compound Interest graphic (click the image for more).

Who knew a nearly-5000 year-old weapon would be effective against such a modern scourge? (Well, yes, virologists, obviously.) The more modern alcohol hand gels do much the same thing, but not quite as effectively – if you have access to soap and water, use them!

Of course, all this only works if you wash your hands thoroughly. I highly recommend watching this video, which uses black ink to demonstrate what needs to happen with the soap. I thought I was washing my hands properly until I watched it, and now I’m actually washing my hands properly.

You may be thinking at this point (if you’ve made it this far), “hang on, if the ancient Babylonians were making soap nearly 5000 years ago, it must be quite easy to make… ooh, could I make soap?!” And yes, yes it is and yes you can. Believe me, if the apocolypse comes I shall be doing just that. People rarely think about soap in disaster movies, which is a problem, because without a bit of basic hygine it won’t be long before the hero is either puking his guts up or dying from a minor wound infection.

Here’s the thing though, it’s potentially dangerous to make soap, because most of the recipes you’ll find (I won’t link to any, but a quick YouTube search will turn up several – try looking for “saponification“) involve lye. Lye is actually a broad term that covers a couple of different chemicals, but most of the time when people say lye these days, they mean pure sodium hydroxide.

Pure sodium hydroxide is usually supplied as pellets.

Pure sodium hydroxide comes in the form of pellets. It’s dangerous for two reasons. Firstly, precisely because it’s so good at breaking down fats and proteins, i.e. the stuff that humans are made of, it’s really, really corrosive and will give you an extremely nasty burn. Remember that scene in the movie Fight Club? Yes, that scene? Well, that. (Follow that link with extreme caution.)

And secondly, when sodium hydroxide pellets are mixed with water, the solution gets really, really hot.

It doesn’t take a lot of imagination to realise that a really hot, highly corrosive, solution is potentially a huge disaster waiting to happen. So, and I cannot stress this enough, DO NOT attempt to make your own soap unless you have done a lot of research AND you have ALL the appropriate safety equipment, especially good eye protection.

And there we are. Soap is ancient and awesome, and full of interesting chemistry. Make sure you appreciate it every time you wash your hands, which ought to be frequently!

Stay safe, everyone. Take care, and look after yourselves.

Want something non-sciency to distract you? Why not check out my fiction blog: the fiction phial. There are loads of short stories, and even (recently) a poem. Enjoy!

If you’re studying from home, have you got your Pocket Chemist yet? Why not grab one? It’s a hugely useful tool, and by buying one you’ll be supporting this site – it’s win-win!

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Butyric acid, a very smelly molecule

Did you know that you’re walking around with an incredibly sensitive chemical detector, capable of detecting and identifying substances at levels as low as 0.2 parts per billion (I’m talking about gases here, but if you think about this ratio in another way it’s about half a second in a century), and possibly even lower? Capable of distinguishing between millions and very probably trillions of different substances and mixtures of substances?


Did you nose you were carrying around a very sensitive chemical detector?

Well you are. It’s your nose. Dogs, of course, can do even better than humans (bloodhounds can easily detect substances in the parts per trillion range) but our noses are still pretty impressive.

We are particularly good with nasty smells, for very sensible evolutionary reasons. If it smells bad it’s probably bad for you, stay away and definitely don’t eat it.

Which brings me to butyric acid, or butanoic acid (to give it its official IUPAC name, which literally no one uses outside of A-level chemistry). Butyric acid is a small molecule, early in the list of carboxylic acids, and you might imagine a chemistry student would meet it, well, if not frequently then at least once or twice during their studies. After all barely a week goes by when we don’t crack open the ethanoic acid (also known as acetic acid, the stuff that gives vinegar its pungent smell).

And yet I managed to go for years and years without ever knowingly coming across the stuff. I knew about its theoretical existence of course, and never really thought about it much beyond that. After all, you can’t use every chemical can you? I obediently followed my lab book instructions and then later specialised in physical chemistry, so the opportunity to fiddle around with cocktails of interesting organic molecules of my own choosing never really arose.


Butyric acid: it’s very stinky.

When I finally did get my hands on a bottle of butyric acid I quickly learned why it had never featured in an undergraduate practical task.

It stinks.

Of horrible things.

Everyone that smells it seems to identify it slightly differently, but descriptions fall out of the: ‘pooh, farts, sick, smelly feet, sweat, gone-off curry, sour milk’ general category of bad smells. Occasionally someone will generously suggest parmesan cheese, but really, it’s not that nice.

It’s not a smell that goes away, either. It’s a stench that just keeps on giving. One of my students managed to get a tiny drop of it on a lab bench and, despite trying to clean it up, the smell lingered for weeks. In fact it was quite interesting. Most people could smell it for about two weeks (as in, they walked into the room and immediately said “ugh, what’s that smell?!”) After that fewer and fewer people immediately reacted, but every now and then someone would walk in and complain of a horrible stink, which by then no one else was really noticing. I assume these were individuals with unfortunately (in this situation) sensitive noses, perhaps with great futures ahead of them as chefs, sommeliers and perfumers. Although some fairly recent research has suggested that ability to recognise smells has more to do with training than innate ability. Still, who nose? (Hehe)

So what is butyric acid and why is it so stinky? It’s name actually comes from the Latin word butyrum (or buturum) meaning butter, because it was first extracted from rancid butter by the French chemist Michel Eugène Chevreul (bet he loved his job). It’s a fatty acid, which means it’s one of the building blocks of fats. The fat molecule made from butyric acid makes up 3-4% of butter, and tied up in this form it’s completely innocuous. However once those fats start to break down, the evil butyric acid starts to be released.


Probably the least offensive thing associated with butyric acid. Probably.

It’s generally found in dairy products, and is a product of anaerobic fermentation (that is, fermentation that happens in the absence of oxygen), hence the links to butter and parmesan cheese. Anaerobic fermentation also happens in the colon. Hence, ahem, the pooh smell. Oh yes, and butyric acid is also what gives vomit that distinctive, smell-it-a-mile-off, odour.

And this, of course, is why we’re so good at detecting it. Humans can pick this stuff up at 10 parts per million (going back to those time analogies, that’s the equivalent of 32 seconds out of a year) which explains why the stench appeared to linger on and on – that single drop of pure butyric acid would have contained something like a thousand trillion molecules. Evolution has trained us to detect and avoid this stuff because it’s very probably a sign of disease and potential infection (gone-off food, vomit, faeces etc). This is stuff we need to steer well clear of to avoid getting ill, and so nature has given us a handy mechanism by which to detect and avoid it, of the “yuck! What is that smell?! I’m out of here!” variety.


From nasty to really quite nice: you can make pineapple scents from butyric acid.

Funnily enough though, it does have its uses. There are molecules called esters which can be made from butyric acid (that’s why we were experimenting with it in the first place) which actually smell rather nice. In particular there’s one that has a lovely apple-pineapple smell, and another that smells of apricots and pears. As a result, these much nicer-smelling substances are used as food and perfume additives.

The salts of butyric acid (butyrates, or butanoates) have interesting effects on the cells that might be in your colon. Butyrate actually slows down the growth of cancer cells in this area, while at the same time somehow managing to promote healthy, normal cells. Exactly how this works isn’t well understood, but it seems to be linked to dietary fibre. Yes, I’m afraid to say you can’t swap cheese for bran flakes and vegetables. You still need to eat your fibre.

Butyric acid also helps to prevent salmonella bacteria from taking hold in poultry, and as result it’s used as a chicken feed additive (lucky chickens). It’s also been used as a fishing bait additive, particularly for carp bait. And perhaps not surprisingly it’s been used, along with a cocktail of other stinky stuff, in stink bombs.

So even the stinkiest of molecules has it’s uses, and maybe it’s not so bad after all. Makes you wonder how anyone ever developed a taste for parmesan cheese though, doesn’t it?
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Tales of asking for evidence: are chia seeds all they’re cracked up to be?

I’ve mentioned it before, but this summer I got involved with Sense About Science’s Ask for Evidence Campaign. This is a brilliant campaign in which Sense About Science (for some reason they never abbreviate their name to initials) encourages people to ask organisations about dubious ‘scientific’ claims. Ever wondered what on earth Boswelox actually is and whether it can really counteract ‘skin microcontractions’? Ask the company for evidence. See what they say. (In that particular case the UK Advertising Watchdog has already weighed in, but you get the idea.)


Are chia seeds all they’re cracked up to be?

I picked up on a few different claims, the first of which had to do with chia seeds. They are the latest health food craze (well, you know, one of latest – this is an area that moves fast, another health food craze could have gone from magical weight-loss aid to dangerous cancer risk in the time it’s taken me to type this), and come with all manner of interesting claims from stabilising blood sugar levels to having “8 times more Omega 3 than salmon“. The trail led back to AZChia, a company set up by Dr Wayne Coates of the University of Arizona. Although, in Dr Coates defence, many of the more hyperbolic media claims don’t appear to have actually started with him, and his work seems to be rigorous.

There are lots of claims out there in the press, but they most seem to boil down to omega-3 fatty acids. Now, there’s a whole other essay to be written on that topic, but essentially (wait for it) these are essential (boom) fatty acids. That means we need them to maintain good health and although there’s some controversy over exactly what they do and don’t affect, there’s no question they’re vital for a healthy metabolism. However they can’t be made in the body (not from scratch, anyway) so we have to eat them. This is potentially tricky for vegetarians because the main source of omega-3 fatty acids is fish oils. But they do turn up in certain plant foodstuffs, and one such foodstuff is chia seeds. In fact, chia seeds biggest claim is that they are the “richest natural plant source of omega-3 fatty acids“.

But before we go any further with this it’s important to realise that there’s more than one type of omega-3 fatty acid. There is a group of molecules that fall into this category, and some of them are tricker to obtain from certain food sources than others. In particular, there’s something called ALA (α-Linolenic acid), another called EPA (eicosapentaenoic acid) and finally DHA (docosahexaenoic acid – these names just get better and better don’t they?).

The main source of these last two, DHA and EPA, is cold-water oceanic fish, like cod and salmon. Both EPA and DHA are converted into prostaglandins which regulate cell activity. DHA is a structural component of such minor essentials as your brain, retina and skin. Make no mistake, you need these molecules.

ALA is slightly different. ALA is available from plants such as, guess what, chia. And also kiwifruit seeds (bizarrely, these have nearly as much as chia seeds), perilla and flax, otherwise known as linseed. Humans cannot make ALA; we have to eat it. However our bodies can make DHA and EPA from ALA.  So, eat your ALA-packed plants and, in theory, you get the complete set.

But it’s not quite that simple (it never is, is it?)  Yes we can synthesise DHA and EPA from ALA, but only poorly. For adults, it might be less than 1% for DHA, and probably less than 5% for EPA (the numbers are slightly higher, although not much, for babies).

Back to that claim that chia seeds have 8 times more omega-3 than salmon (not, I should stress, a claim actually made by Dr Coates). It is true? Well, 100 g of salmon contains roughly 0.4 g of ALA, whereas 100 g of chia seeds contains more like 18 g. So that’s actually a lot more than 8 times. On the other hand, chia seeds contain no DHA or EPA (fish sources, remember) whereas salmon will give you about 1.4 g and 0.4 g respectively. Chia seeds may contain more omega-3 in total than salmon, but it’s not the good stuff. There’s none of the DHA that’s so important for healthy brain, skin and eyes. You might be able to convert a little bit from the ALA that is there, probably enough to get by (particularly if you’re a vegetarian or a vegan and willing to eat a lot of seeds), but oily fish really is the best source.

What about the claim that chia seeds are the richest plant source of omega-3 fatty acids? I pressed Dr Coates for evidence of this, since it’s a statement he makes on his website, and his response was as follows:

“No one paper is going to say that. You are wanting something that does not exist to my knowledge. You would need to compare hundreds of analyses and papers, determine good analyses from bad, etc. Different harvest cycles, growing locations, varieties, all affect the numbers so impossible to really do it. The statement is based on years of work and knowledge.”

So tricky to prove, but probably true. Possibly.

There is a little more to this story. Chia seeds are often promoted as a whole food, packed full of many nutrients over and above omega-3s. A ‘super-food‘, if you will. They do indeed contain a whole range of nutrients. But Dr Loren Cordain, author of the book The Paleo Dietcontends that chia seeds also contain high levels of phytate.  Phytate is the salt of phytic acid, and is a substance that binds minerals such as calcium, iron, zinc, magnesium and copper, making them unavailable for absorption by the body. As a result, chia seeds are actually quite a poor source of these minerals. And, as with all plants, it’s a similar situation with vitamin B6 – it’s something we absorb far more effectively from animal sources. In short, just because something’s in a plant, doesn’t mean we can make use of it.


If you’re not a vegetarian, stick to your oily fish.

So, in summary, should you be sprinkling chia on your breakfast cereal? Well, it probably won’t do any harm. If you’re a strict vegetarian or vegan they may be worth considering, although they’re probably not worth paying a lot of money for. If you’re a meat eater, you’re almost certainly better off sticking with oily fish – it’s a much better source of the really essential fatty acids.


I also investigated some other claims for Ask for Evidence, one of which was the statement made by Health Journalist Hazel Courteney on national radio that “the average person absorbs into their bloodstream alone about 14 kg of toxins annually through their skin.” There is more to follow on this particular story, and it should appear on the Ask for Evidence page shortly.

There was also something on anti-bac pens which I’ll discuss next time. Watch this space!

The chemistry of chocolate

A lot of people believe there’s a deep religious significance to the holiday we’re enjoying right now.  Others argue it’s older than that: an ancient spring festival, celebrating the spring equinox, fertility and new growth.

funny-chocolate-Periodic-Table-chemistryBut every child knows what Easter is really all about.  Yes.  Chocolate.  Yummy, delicious chocolate.

So with that in mind, let’s talk a little about the chemistry of chocolate.  For it is very interesting stuff.  What’s in the lovely, creamy, sweet brown stuff?  And how do they get it to melt so perfectly in your mouth?  And does it really give you a happy high?

How do they get chocolate to melt so perfectly at body temperature?  There is more to this than you might imagine.  First of all you have to know something about crystals.  Most people, upon hearing the word crystals, think about clear, shiny things twinkling from from Katie Price’s latest wedding dress.  But in fact lots of substances form crystals, because a crystal is just a piece of any solid material that has regular shapes arranged symmetrically.  Crystals don’t have to be transparent.  Metals are crystalline.  Pure iodine forms rather pretty grey-silver crystals.  And, crucially, fat also crystallises.

In fact the fat in chocolate, cocoa butter, can crystallise in many different forms.  Only one of these is the lovely, hard, shiny one that is so nice and snappy at room temperature.  If you’ve ever cooked with chocolate, or indeed just left it in the car on a hot day by accident, you probably know that if you melt it and then just let it solidify again the result is dull-looking and crumbly.  Getting the right form of chocolate crystals to form is called tempering, and it’s a complicated business.  First the chocolate has to be melted at a high enough temperature to melt all the crystals.  Then it needs to be cooled to just the right temperature for the best crystals to grow, then agitated, then warmed up a tiny bit (but not too much), then cooled again.  There are other methods, but this is the one that’s used in the big chocolate factories.  Just ask the Oompa Loompas.

This ideal fat crystal form not only looks good and snaps nicely, it also melts at 34 oC.  Normal body temperature is actually around 36 oC, with the oft-quoted 37 oC actually being a tad on the high side.  Skin temperature, on the other hand (geddit?), is somewhere between 32-35 oC depending on how warm the environment is.  This means that chocolate will just about stay solid in your fingers if you don’t hold it too long, but put it in your mouth and the temperature is just right to melt it perfectly, releasing delicious sweetness, creamy fats and other chemicals that stimulate your tastebuds and give chocolate its flavour (craving your easter eggs yet?)

What about the other question: does chocolate really give you a ‘happy high’?  Well, it turns out there’s a whole cocktail of naturally-occurring bioactive chemicals (some people see ‘natural chemicals’ as a bit of an oxymoron and that’s ironic in a way, since the very brain that learned big words like oxymoron is actually stuffed full of natural chemicals that make it work) in chocolate.  Firstly, caffeine, otherwise known its less tongue-tripping name of 1,3,7-trimethylxanthine, but we’ll stick to caffeine.

We’re all familiar with caffeine from tea and coffee, and that drink that’s falsely advertised as giving you wings, but its presence in chocolate is sometimes forgotten.  It is of course a stimulant, exciting the central nervous system (it’s very excitable), boosting heart rate and contracting muscles.  It also acts on receptors in the brain and causes them to release pleasure-producing chemicals.  There isn’t a lot in chocolate though: it varies by type but even in the darkest of dark chocolate, there’s generally less caffeine than you’d get from even a single cup of tea.  Milk chocolate has even less and white chocolate has none at all.

But there’s more of another chemical, also a stimulant: theobromine.  This is interesting stuff.  It’s a heart stimulant and, like caffeine, a diuretic (it makes you wee).  More recently it’s use as a potential treatment for cancer tumours has been investigated.  There is roughly eight times more theobromine in chocolate than caffeine, but we metabolise it quickly so it doesn’t hang around in our bodies for long.  It’s less safe for animals: as any responsible dog owner will tell you, chocolate is very bad for dogs.  This is mostly due to the theobromine (the caffeine isn’t great either, but there’s not so much of that).  If your pooch gets into your Easter eggs, they could suffer nausea and vomiting, diarrhea, muscle tremors and, potentially, heart failure.  So keep your eggs out of reach.

It’s not just stimulants.  Chocolate also contains fatty acids called cannabinoids.  Guess what they’re similar to?  The clue is in the name… yes, their cousin is called tetrahydrocannabinol, and it’s found in the cannabis plant.  When cannabinoids hit the brain they make you feel relaxed and intoxicated.  And that’s not all, chocolate also contains phenethylamine, sometimes dubbed ‘the love drug’ because levels increase in the body when you’re feeling romantic.  Although there isn’t much and it’s metabolised too quickly to  have a significant effect.

So with this delicious swirly mixture of stimulants and suppressants, surely chocolate ought to be on some sort of controlled drug list?  Well, no.  All of these chemicals are present in relatively small amounts, and have a limited effect on the body (human bodies anyway).  People who suffer chocolate cravings aren’t satisfied by just swallowing capsules that contain the relevant chemical compounds, but eating white chocolate – which contains no cocoa solids and therefore none of the psychoactive ingredients – does the trick.  This suggests that the real reason we like chocolate is simply the same reason we like cream cakes: lots of sugar and fat – yummy!

So now you’ve stuffed your brain full of sciencey-stuff, go ahead and stuff your mouth with lots of yummy chocolate.  Happy Easter!

P.S. have you noticed that it’s kem-is-try but cho-ko-late?  This alliteration spoiling bit of linguistics is because the word chemistry derives from the word alchemy, which (probably, people argue over these things) comes from the ancient Egyptian name for Egypt – khem or khame, or khmi.  Hence al-khmi, ‘the Egyptian art’.