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It's Christmas Eve and the final day of #ChemAdvent!

We're finishing off with Christmas pudding and why you shouldn't hide a coin in the mixture as was customary in the past 🪙

Infographic on the chemistry of Christmas puddings. The graphic shows the chemical structures of tartaric acid (from raisins) and citric acid (from citrus peel). It also explains how the custom of hiding small silver coins in the mixture is not advisable with modern coiins due to their nickel content.

Day 23 of #ChemAdvent!

Prawns turn red-orange when cooked as the compound astaxanthin is revealed 🟠

Bells are fashioned from tin bronzes, with trace elements improving the material properties and sound 🔔

Guess the very tenuous, silly, and non-chemical connection that led me to pair these ones?

Infographic on the composition of bell metals, which are commonly made of tin bronzes (75% copper and 20% tin, with other metals making up the balance).

Infographic on the chemistry of prawns. It explains how the compound astaxanthin changes from a protein-bound to a free form when prawns are cooked, revealing its orange-red colour.

Keeping warm on day 22 of #ChemAdvent 🔥

Winter fire smells come from smoky syringol and guaiacols.

Herring under a fur coat doesn't actually involve a fur coat, but a layer of beetroot and vegetables over pickled herring

Infographic on the smell of winter fires. The structures of several compounds that contribute to the smell of winter fires are shown, including guaiacol, syringol, isoeugenol and 4-methylguaiacol.

Infographic on herring under a fur coat, a layered salad which includes pickled herring, grated boiled eggs, vegetables, onion and mayonnaise. A layer of grated beetroot gives the dish a vivid purple colour, due to the pigment betanin, the structure of which is shown.

Terpenes unite the graphics for day 21 of #ChemAdvent

Menthol in candy canes is responsible for the cooling sensation in your mouth when you eat one ❄️

The muddy flavour of carp is dominated by the compound geosmin, another terpene 🐟

Infographic on candy canes. The chemical structures of sucrose and menthol are shown. Menthol from peppermint triggers cold-sensitive receptors when eaten, making your mouth feel cold.

Infographic on carp. The earthy flavour of freshwater fish is due to the compound geosmin, produced by bacteria. The structure of geosmin is shown.

Some cracking chemistry for day 20 of #ChemAdvent!

First up are Christmas crackers, taking advantage of friction-sensitive silver fulminate to deliver a big bang 💥

For tamales, preventing cracking of the corn husk wrapping is the aim, so they're soaked in water to make them flexible 🌽

Infographic on Christmas crackers, showing the structure of silver fulminate and explaining how this friction-sensitive compound is placed on the ends of the two strips of card that form the cracker snap and detonates when the snap is pulled.

Infographic on tamales, made from a corn-based dough and steamed inside a corn husk. Nixtamalisation is the process of cooking and steeping corn kernels in an alkaline solution to degrade the outer layer of the corn kernel and soften the corn, making it easier to grind into flour.

Mulled wine and tangyuan for day 19 of #ChemAdvent!

Both wine and tangyuan contain long, chainlike molecules. In wine, it's the polymeric tannins that influence astringency and mouthfeel.

In tangyuan, made from glutinous rice flour, branched chains of amylopectin make the rice sticky

Infographic on mulled wine, showing the structures of two key flavour compenents: eugenol from cloves and cinnamaldehyde from cinnamon.

Infographic on tangyuan, Chinese dumplings made from glutinous rice flour. Low amylose content and higher amylopectin content makes glutinous rice sticky. Simplified structures of amylose and amylopectin are shown.

Very contrasting smells for day 18 of #ChemAdvent!

Olibanic acid isomers contribute to the fragrance of Frankincense, traditionally associated with Christmas.

The aroma of hákarl, fermented Greenland shark, is a much less welcome one, dominated by ammonia and other pungent compounds.

Infographic on frankincense, showing the chemical structure of olibanic acid isomers, the key compounds responsible for the characteristic aroma of frankincense.

Infographic on harkal, fermented Greenland shark, traditionally eaten ad part of the mid-winter festival Þorrablót. It contains urea, trimethylamine oxide and ammonia, which dominate the pungent smell and taste of the fish.

Decorations and wrapping for day 17 of #ChemAdvent!

Baubles were traditionally silvered using the reduction of silver nitrate with glucose - a chemical test used in classrooms to detect aldehydes.

Wrapping paper and tape are both cellulose-based 🎁

Infographic on how baubles are silvered using silver nitrate solution, concentrated ammonia and glucose solution. Glucose reduces the silver ions to silver metal. The chemical structures of silver nitrate and glucose are shown.

Infographic on wrapping paper and tape. Both are based on cellulose, with tape also containing a pressure-sensitive acrylic or rubber-based adhesive. The structure of cellulose is shown.

Fermentation is the chemical connection for day 16 of #ChemAdvent: both Korean kimchi and Inuit kiviak take advantage of lactic acid bacteria fermenting carbohydrates and producing flavour compounds.

Infographic on kimchi, explaining how lactic acid bacteria produce key flavour compounds. A selection of flavour compounds are shown, including dimethyl trisulfide from garlic and onions, 2,3-butanedione which has a buttery flavour, and beta-phenyl acetate which has a rose/honey/sweet flavour.

Infographic on kiviak, an inuit delicacy eaten on special occasions, including Christmas. It's made by packing hundreds of little auks into a seal skin then fermenting them for 18 months. Lactic acid bateria ferment carbohydrates producing flavour compounds. A reaction scheme shows the lactic acid fermentation of glucose, starting with glucose, passing through 2-pyruvic acid and producing lactic acid.

For day 15 of #ChemAdvent, the most tenuous connection so far.

Deep-fried caterpillars are a Christmas delicacy in South Africa, and tinsel... kind of looks like a giant sparkly festive caterpillar?

Yeah, it's a stretch.

Infographic on the chemical history of tinsel, from the use of shredded silver pre-1900, to the use of aluminium and lead foil, through to the polyvintyl chloride used today.

Infographic on deep-fried caterpullars, a Christmas delicacy in South Africa. The graphic compares the protein and iron content of the mopane worm (57% and 31-77 mg per 100 g respectively) to that of beef (22% and 6 mg per 100 g)

For day 14 of #ChemAdvent, we've got two fruity-themed graphics.

The first is on festive flamethrowers with orange peel and limonene 🍊 🔥

The other is on nastar, Indonesian pastry-based desserts filled with spiced pineapple jam 🍍

Infographic on orange peel flamethrowers, explaining how the presence of flammable D-limonene in orange peel oils makes it very flammable. The structure of D-limonene is shown and there's also a safety disclaimer.

Infographic on nastar, Indonesian pastry-based desserts filled with spiced pineapple jam. The structures of some key chemical contributors to pineapple flavour and aroma are shown; these include esters, such as ethyl-2-methylbutanoate and allyl hexanoate, and furaneol, also known as pineapple ketone.

St Lucia's Day links day 13 of #ChemAdvent: The saint is often depicted with a wreath of candles around her head, and in Sweden they celebrate with saffron buns (lussekatter)

Infographic showing how a blown-out candle can relight when a match is held in its smoke trail. The “smoke” is wax vapour that ignites. An example wax combustion equation is also shown.

Infographic about Swedish lussekatter saffron buns. Saffron gives colour via crocin and flavour from picrocrocin and safranal, the molecular structures of which are shown.

More vibrant anthocyanins link the graphics for day 12 of #ChemAdvent: they colour both cranberries and puto bumbong, steamed purple rice cakes eaten in the Phillipines at Christmas.

Infographic on cranberries antioxidants showing the chemical structure of quercetin. Quercetin is a polyphenol antioxidant in cranberry which may have positive health effects in humans. Suggestions that cranberry juice is an effective treatment for urinary tract infections have not been proven in research studies.

Infographic on puto bumbong, steamed purple rice cakes eaten in the Phillipines at Christmas. Anthocyanin pigments such as cyanidin 3-glucoside and peonidin 3-glucoside, the structures of which are shown in the graphic, give the rice its purple colour. The rice lightens when cooked as the bran (the outside of the rice grain) mixes with the endosperm (inside the rice grain).

For day 11 of #ChemAdvent, we have a slightly tenuous medicinal link... 💊

Theobromine, found in holly berries (and chocolate), is prescribed for persistent cough in South Korea 🇰🇷

Opioids are well known for their painkilling abilities and appear in trace amounts in poppy seed bejgli from Hungary 🇭🇺

Infographic on holly and ivy. Holly berries contain bitter alkaloids such as theobromine, the structure of which is shown on the graphic. Poison ivy contains a the other compound depicted, urushiol, which can irritate the skin.

Infographic on bejgli, a sweet roll eaten in Hungary that is filled with poppy seeds, walnut paste or chestnut paste. The poppy seeds can contain trace amounts of opioid compounds such as morphine and codeine (the structures of which are provided in the graphic), which can cause opiate-positive urine test results.

Two poisonous plants for day 10 of #ChemAdvent! ☠️

Brazilian farofa is made from cassava flour, itself made from cassava roots which are soaked to remove toxic cyanogenic glycosides.

Mistletoe is much less likely to be eaten but is also toxic due to the presence of toxic peptides and tyramine.

Infographic on the chemistry of mistletoe. It explains how mistletoe leaves are mildly toxic due to the presence of toxic peptides, as well as the alkaloid tyramine. The structure of tyramine is shown between two mistletoe leaves.

Infographic on farofa, a Brazilian side-dish also used as a stuffing for turkey or chicken. Farofa is made from cassava flour, made itself from cassava roots. Cassava roots contain toxic cyanogenic glycosides and must be soaked to remove these compounds. The sturcture of linamarin, the main cyanogenic glycoside in cassava root, is shown.

Day 9's #ChemAdvent entries are linked by ginger - a key component of gingerbread and also one of the spices found in rooster doro wat, an Ethiopian spicy chicken stew eaten after periods of fasting, including at Christmas 🫚

Infographic on gingerbread graphic that highlights the chemical transformation that ginger undergoes when cooked, and shows the chemical structures of gingerol (before cooking) and zingerone (after cooking).

Infographic on rooster doro wat that highlights the ingredients of the spice mix used, including holy basil, cardamom, fenugreek and ginger. The structures of sotolon (component of fenugreek), linalool (component of coriander seeds) and 1,8-cineole (component of cardamom seeds) are shown.

For Day 8 of #ChemAdvent, mince pies and dulce de noche buena are connecting by fruit acid contributions to their flavour: tartaric acid from raisins in mince pies and the notorious vomit-like butyric acid in papaya 🥧

Infographics on mince pies and papaya. The mince pie infographic highlights mince pie ingredients (suet, dried fruit and spices) and shows stylised chemical structures of tartaric acid (from raisins) and eugenol (from cloves). The second infographic focuses on dulce de noche buena, a combination of different fruits in syrup including papaya. Structures of linalool, benzaldehyde and butyric acid, key flavourants in papaya, are shown.

Almost forgot to share today's #ChemAdvent! Day 7's subjects are linked by milk: seasoned and spiced for eggnog, evaporated, condensed and baked for tres leches cake 🥛

Two food-chemistry infographics. The first explains eggnog flavour chemistry, showing stylized molecular structures of cinnamaldehyde from cinnamon and sabinene from nutmeg around a glass of eggnog. The second presents the chemistry of Nicaragua’s tres leches cake, with a photo of a slice topped with whipped cream and a cherry, plus a diagram of lactose and sugar contents for whole, evaporated, and condensed milk.

Brussels sprouts and Finnish lanttulaatikko feature in day 5 of #ChemAdvent. Their chemical connection is glucosinolates, bitter compounds in sprouts and swedes.

Genetic variations in people affect the perception of this bitterness – so if you're not a sprouts fan, that could be why!

Day 4 of #ChemAdvent has a polymer theme!

Long polymer chains are key to sodium polyacrylate's ability to act as fake snow, and also form the water-trapping network in aspic jellies.

#ChemAdvent

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