Of course, not everyone celebrates Christmas. But when December rolls around, the Yuletide vibe can be pretty hard to avoid. Christmas decorations have been up for months, we’re hearing seasonal carol muzac piped into supermarkets, smelling the gingerbread, tasting the peppermint candy canes from the office Kris Kringle and feeling the crunch of baubles underfoot.
What is the science behind five festive sensory experiences?
The unmissable bang of a Christmas cracker
Along with the obligatory bad joke, colourful paper crown and throwaway gadget, every Christmas bonbon worth its tinsel contains a cracker snap.
Crackers were invented by confectioner Tom Smith in the 1840s to package and boost sales of sugared almonds, according to the Victoria and Albert Museum.
The cracker snap comes from two thin pieces of card joined together which hopefully explode when pulled apart.
That satisfying sound is created by a small quantity of the compound silver fulminate (AgCNO) painted on the end of one strip, which is connected to another strip of cardboard that’s coated with an abrasive, sandpaper-like material.
Silver fulminate is unstable, made by reacting concentrated nitric acid with silver and ethanol. When you pull a bonbon with a friend, the small amount of friction you generate creates its explosive reaction.
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Apparently, the propensity of silver fulminate to self-detonate is so great, that it can only be used in tiny amounts. That’s because the fulminate ion (the carbon, nitrogen, and oxygen part) is unstable. The nitrogen-oxygen bond is weak, because nitrogen prefers to bond with nitrogen instead. So, when a cracker is popped, the substance reacts to form nitrogen gas, carbon dioxide gas and metal salts.
Speaking of bad cracker jokes:
Q. How do Christmas trees get ready for a night out?
A. They spruce up!
The smell of pine needles
There are many aromas associated with Christmas – the summery sniff of sunscreen, or the roasty anticipation of cooked turkey, or tofurkey.
For many people the smell of a pine tree is inherently festive, although for others that signature scent might evoke the smell of old-fashioned wooden toys, or even toilet cleaner.
But what makes the scent so distinctive? A study published in Nature sought to describe the diverse substances and smell compounds – called odour-acting substances – that make up what we know as the Christmassy smell of pine tree.
Researchers considered samples of Scots pine sourced appropriately from a Bavarian forest – O’Tannenbaum if you will.
To break down the aroma into its component parts they used a combination of human sensory analysis (two panels of smellers, one novice, one trained) together with two odour-analysis techniques – gas chromatography-olfactometry (GC-O) to separate the component volatile compounds and aroma extract dilution analysis (AEDA).
The expert human panel characterised the smell of Scotts pine as including whiffs of: resin, citrus, herb, pepper, frankincense (which apparently smells musty, soft and sweet) and carpenter’s shop, with touches of wood glue.
The odour analysis techniques were then used to unpick the underlying 44 compounds contributing to the scent.
The most potent of the forty-plus parts included: a-Pinene (which has a woody, resinous smell), Nona – 2,4 – dienal and Deca -2,4 – dienal (offering a fatty tinge), Pentanoic acid (cheesy apparently), heptanoic acid (pepperoni), Pentyloxan -2 – one (coconut-like), a fruity smelly trideca trienal, peppery a-Bisabolol, vanilliin and phenylpropanoic acid (vomity, fruity)
And, also thymoquinone (which delightfully smells like pencils).
Read more: A Christmas Tree-t: Our 9 favourite tree stories of 2021
Time for another cracker joke before we move on to the next festive sense?
Q: What do you call someone who steals Gingerbread Men?
A: A crook-ie.
Sight – when food has a face we prefer not to eat it
Do you imagine a gingerbread person has personality, like the Gingerbread Man in Shrek? Maybe you nibble the legs a little first, delaying the prospect of biting its head off?
You might think a gingerbread cookie tastes the same no matter what shape it is.
But research published in the Journal of Consumer Psychology found when food is given human-like features, people do not like to eat it.
Anthropomorphism – attributing human characteristics – has long been a popular marketing strategy for food products (think talking M&Ms, or the Australian company that puts smiley faces on pies).
Read more: When food has a face, people prefer not to eat it
But the results of five different experiments testing people’s responses to food with a face found that while consumers might like to purchase humanised food products like gingerbread men, most prefer not to eat them.
The exceptions, the study says, are ‘cold-hearted’ people who lack empathy or remorse.
What about the tastes of Christmas?
Spices are a common ingredient in many Christmas-associated foods and drinks – Gluwein, eggnog, advent tea, Christmas pudding, mince pies and more.
It makes sense, given that scientists have discovered spices offer a range of intoxicatingly cheerful effects.
Spice plants generally evolved chemicals to protect them against herbivorous insects and vertebrates, fungi, pathogens, and parasites, so many offer us humans antioxidant, antimicrobial, and antiviral properties. For instance, lab tests show Christmas spices like cloves, cinnamon and allspice inhibit some 75% of common bacterial species, according to Bioscience.
Studies in mice have suggested that phytonutrients called caffeic acid (found in pudding spices like cinnamon, cumin, nutmeg, ginger, star anise, or stuffing additions like caraway, thyme, oregano, sage and rosemary) might help reduce the rise in blood sugar levels after eating, and even potentially offer some beneficial effect due to converting potential cancer-causing substances into less toxic compounds.
Read more: Mixed spice
The touch and feel of wrapping paper and ribbons
Do you spend hours on Christmas eve wrapping presents?
While a stack of carefully wrapped pressies in red and green, silver and shiny metallics, or low key kraft paper – certainly contributes visually to the Christmassy tone of the household, it might be worth giving some thought to the touch and feel as well.
Marketing and consumer studies have researched the effect of packaging choice and materials on our experience of different products. It turns out the wrapping can affect our judgement of what’s inside.
In the 1930s Ad man Louis Cheskin called this experience ‘sensation transference’ – where the consumer cannot separate their feelings and perception of a product from its packaging.
In 2018, a psychologist from Oxford synthesised the research in a book chapter on Tactile/Haptic Aspects of Multisensory Packaging Design.
Weight is an important factor. Studies of products – everything from drinks to chocolates to lipstick – have found people rate items wrapped in heavier packaging as having a more intense smell, being more satisfying and of higher quality.
Consumers report soft drinks and beer taste better when thought to have come from a bottle rather than a can. Chocolates in a heavier box received higher ratings for desirability, willingness to pay and flavour intensity than the exact same chocolates offered in a lighter box.
Of course shape plays a part. Certain arbitrary packaging forms come to take on a specific meaning (or association) after being repeatedly linked to a particular product, brand, or category. Think of premium icecream – usually sold in a cylindrical rather than square shaped container.
All of which might lead you to think that wrapping your Christmas presents in fancy heavy and peculiarly shaped paper might help convey appreciation for the gift inside.
Read more: The science behind our sense of touch
But if you can’t be bothered, there is good news.
In another experiment 180 university students were gifted a coffee mug for participating in a bogus study.
Even though apparently all 180 were supporters of a particular basketball team, the Miami heat, half were given a Miami heat mug and half an Orlando magic mug. Mean!
The researchers found that those who received a sloppily wrapped gift liked their present significantly more than those who received a neatly wrapped gift – regardless of which mug they were given. The researchers said the tidiness of the wrapping set expectations, so those with a neatly wrapped gift were more likely to be disappointed.
