News and Views

Opinion: The chemistry of Christmas

21 Dec
(l-r): UCC’s Carol McCarthy and Dr Abina Crean, researchers in the Synthesis and Solid State Pharmaceutical Centre.

Understanding the chemistry of our festive food and drink and how they affect our body, according to UCC’s Carol McCarthy and Dr Abina Crean, and UL's Dr Sarah Hayes, researchers in the Synthesis and Solid State Pharmaceutical Centre.

Christmas is the time of year when we all take a break to relax, unwind and spend time with friends and family. We eat, we drink and some of us get a little too merry! What you might not realise is that understanding the chemistry of our festive tipples and how they affect our body can help us to combat the dreaded next day hangover.

Lighting the Christmas pudding is a famous Christmas tradition. As you pour a generous splash of brandy over the pudding, you’ll notice the flame is an unusual blue colour, very different to the warm yellow flame of burning coal and candles. This blue flame is a result of complete combustion which occurs when you burn alcohol (CH3CH2OH). Complete combustion happens when there’s enough oxygen to only produce carbon dioxide (CO2) and water as products. Ethanol burns more completely than other hydrocarbon fuels like coal and candle wax, which tend to produce carbon atoms (also known as soot) and carbon monoxide as well. Yellow flames are indicative of incomplete combustion products.

Thankfully, the blue flames we see don’t burn our Christmas puddings. This is because it’s the vapour associated with the alcohol rather than the pudding or the liquor which is on fire and the flame never reaches the pudding itself. To set a Christmas pudding alight, the liquor must be warmed beforehand - otherwise there will be no vapour to ignite. Once burning, the heat generated warms the liquid alcohol in the pudding, creating more vapour until eventually there is no more alcohol left to vapourise. At this point, the flame burns out, the pudding is left tasty and un-charred and you hopefully won’t have burnt the house down.

Another piece of Christmas chemistry is what happens when we pop open a bottle of something bubbly at New Year. Before you pop the cork, the liquid in the bottle looks almost complete bubble-less. Carbon dioxide is dissolved in both the liquid and the vapour in the bottle. An equilibrium or balance exists between the CO2 in both phases. The pressure in a champagne bottle is between five and six atmospheres. In contrast, most car tyres have an approximate pressure of 1.5 to 2.5 atmospheres. 

When the cork is popped, a pretty cool piece of chemistry occurs. The CO2 in the vapour at the top of the bottle is released leading to an imbalance in the equilibrium between CO2 in the vapour and the liquid. To recover a new stable equilibrium, almost all of the CO2 dissolved in the liquid must escape, creating lots of bubbles. Almost five litres of carbon dioxide gas is released from a typical 0.75 litre bottle of champagne. Incredibly, a glass of champagne releases approximately 20 million bubbles of carbon dioxide! 

So what kind of chemistry occurs when we over-indulge a little too much on our prosecco and festive spirits? It’s worth pointing out at the beginning that a number of factors can affect the severity of a hangover including genetic factors, health, age, sleep and (of course) the amount of alcohol consumed.

Alcohol is a diuretic (which is why the queues are always so long in the toilets in pubs) and inhibits the pituitary secretion of anti-diuretic hormone (ADH; vasopressin). The reduced levels of ADH prevent the kidneys from reabsorbing water and results in dehydration (symptoms of dry mouth, thirst and headache). Drinking 50 g of alcohol in a 250 mL beverage causes the body to eliminate 600-1,000 mL of urine (up to four times as much water is lost as gained). It’s a good idea to drink water while you’re out or before going to bed as it will help reduce dehydration symptoms.

Another hangover suspect is a compound produced by the metabolism of alcohol. Alcohol, or more specifically ethanol, is broken down by enzymes in the liver into acetaldehyde, which is subsequently broken down by another enzyme into acetate. Acetate can be broken down into carbon dioxide and water. Your body is capable of breaking down alcohol at a rate of around one unit (8 grams or 10 millilitres of pure alcohol) per hour, though this rate will vary marginally from person to person, depending on a number of factors such as their weight, height, metabolic rate etc. Alcohol also disrupts our bodies natural circadian rhythms, we fall asleep quickly after a few drinks, but frequently wake up feeling jetlagged.

Acetaldehyde is the particular compound that’s been implicated in hangovers. It’s a toxic compound, which is usually broken down very quickly into acetate. However, the enzyme that converts ethanol to acetaldehyde works faster than that which converts acetaldehyde to acetate, leading to a build-up of acetaldehyde if you have several drinks in a row.

It’s been suggested that acetaldehyde’s toxic effects on cells may play a part in the development of hangover symptoms, particularly nausea, sweating, increased heart rate and headache. There’s still no definite answer one way of the other as to the extent of acetaldehyde’s involvement, though studies have found that the concentration of acetaldehyde in the blood of test subjects didn’t show significant correlation with hangover severity. It may well play a part, but it seems likely that it isn’t the major player.

Some of the old wives’ tales about alcohol consumption and hangovers have also been investigated so which works best?

Old Wives’ Tale No 1 – does the type of alcohol matter?

Most alcoholic drinks will contain a whole range of other chemical compounds as well as ethanol, and these compounds are generally referred to as congeners. Different drinks have different levels of congeners; for example, brandy, red wine and whiskey have much higher congener levels that drinks such as beer, vodka and gin. It’s suggested that higher congener levels could increase the severity of hangover symptoms the next day.

Old Wives’ Tale No 2 – can men drink more than woman?

When you compare men and women of the same height, weight and build, men tend to have more muscle and less fat than women. Muscle tissue has more water than fat tissue, a given dose or amount of alcohol will be diluted more in a man than in a woman. Males also have higher stomach metabolism of ethanol (ADH) than females.

There’s a lot more work to be done to enhance our knowledge of the science of hangovers so it’s difficult to prescribe an effective cure. To alleviate the symptoms of a hangover (especially headache), rehydration with water and electrolytes is recommended. This can be in the form of water, isotonic sports drinks or rehydration salts that can be purchased in a pharmacy. Interspersing non-alcoholic drinks with alcoholic ones on a night out can also help to reverse the effects of low blood sugar and dehydration.

Taking antacids can help with stomach pain or irritation, as ethanol irritates the lining of the stomach and increases the production of gastric acid. Painkillers such as aspirin and ibuprofen can be taken to ease headache symtoms. However, these anti-inflammatories can upset the stomach which can already be in a delicate state.

Paracetamol is an alternative that is gentle on the stomach. Soluble preparations will enter the bloodstream and produce a therapeutic effect more quickly than conventional tablets and capsules.

However, this also comes with a warning, as paracetamol is metabolised by the liver which has already been working overtime to metabolise ethanol, particularly if you have been drinking excessively. Even if you have not been drinking excessively it is vital to ensure that you take the correct dosage of paracetamol as the liver can only metabolise a certain amount of paracetamol at a time and if too much is taken it can lead to acute liver failure.

Paracetamol (acetaminophen) overdose is reportedly the main cause of acute liver failure in the US and UK, so it’s definitely best to follow the instructions before popping the pills.

Fruit juice can help soothe the effects of a hangover by replacing lost glucose supplies. Coffee and caffeinated energy drinks are both diuretics and should be avoided as they compound the diuretic effect of alcohol and will dehydrate you further. Compassion and words of comfort from loved ones always help during a hangover and when you’re able for it – a long stroll in the fresh air!

It goes without saying that the best way to cure a hangover is to try not to get one in the first place. Merry Christmas!

Carol McCarthy is a PhD student at the School of Pharmacy and Synthesis and Solid State Pharmaceutical Centre (SSPC) at UCC. Dr Abina Crean is a lecturer in Pharmaceutics and a researcher at the SSPC at UCC. Dr Sarah Hayes is the Education and Outreach Officer at the SSPC at UL.

University College Cork

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College Road, Cork T12 YN60

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