Compound Interest: The Chemistry of Mulled Wine

There are few things more warming than a mug of mulled wine in the depths of December. Exact recipes may vary, but they all include a common core of ingredients, each of which contributes something to the final flavour. This graphic examines some of the key chemicals that each ingredient adds into the mix, with more detail on each provided below.

Wine

The obvious place to start is with the ingredient which makes up the body of the drink. Red wine is essentially one big, pleasant cocktail of chemicals – like all alcoholic drinks, it contains ethanol, but it also contains a range of other organic compounds which influence its taste and colour. A class of chemicals called anthocyanins provide some of the colour, and can also interact with other chemicals in wine called flavonols to influence the wine’s hue. Some bitterness comes from another chemical group, the flavan-3-ols, whilst much larger organic molecules, known as tannins, impart astringency. There’s much more detail on the chemistry of red wine in this previous post on the site.

Oranges & Lemons

Citrus fruits are another key ingredient, and they have a large bearing on the flavour of the mulled wine. Orange peel alone contains a huge number of compounds: terpenes, tannins, saponins, and phenols, to name but a few of the compound classes that can be found therein. One compound, d-limonene, is a significant contributor to the aroma of oranges, and considerable amounts of it can be found in the rind of citrus fruits – it constitutes 98% of the essential oil obtained from orange peel.

Fruit acids also have a hand in the eventual flavour of the wine. These include compounds such as citric acid, which is responsible for the sour taste of lemons, ascorbic acid, more commonly known as vitamin C, and malic acid, which is found in much more significant quantities in apples.

Sugar

Most mulled wine recipes call for an appreciable amount of sugar, or, to give it its chemical name, sucrose. The particular arrangement of the sucrose molecule, and other molecules that taste sweet, for that matter, is the reason we experience a sweet taste when we eat it. The ‘sweetness triangle’ theory states that, for a molecule to taste sweet, it must have three key areas that are specific distances apart from each other:

1 – a group of atoms which has a hydrogen available for hydrogen bonding.
2 – a group of atoms which has an oxygen atom available to form hydrogen bonds.
3 – a non-polar atom or group of atoms which doesn’t form hydrogen bonds.

To put it more simply, these features are thought to be necessary to make the molecule fit the receptors that detect sweetness on your tongue. In theory, the better a molecule fits the ‘sweetness triangle’, the sweeter it tastes!

Cloves

Cloves are one of the key spices required for the making of mulled wine, imparting a spicy, aromatic flavour. This is largely down to the presence of the compound eugenol, which makes up a large portion of the essential oil that can be extracted from clove buds. Other compounds present in smaller quantities include 2-heptanone, which has a fruity, spicy odour, and methyl salicylate, more commonly known as oil of wintergreen, which has a sweet and somewhat medicinal smell.

Eugenol also has a mild anaesthetic effect, which is one of the reasons that clove oil is occasionally used as a traditional remedy for toothache. This was explored previously in a past post on the site.

Nutmeg

Nutmeg is another spice commonly added to the mulled wine infusion. Sabinene is one of the main constituents of the essential oil, and contributes to the flavour, but a mix of other compounds are also responsible. These include members of a family of compounds called phenol ethers, which include safrole, myristicin, and elemicin. Myristicin actually lends nutmeg hallucinogenic qualities, but only in doses larger than those commonly used in cooking and mulled wine making. Allegedly, the effects of ingesting the nutmeg required are none-too-pleasant, so it isn’t an experience that comes recommended!

Cinnamon

Finally, the sweet, aromatic flavour of cinnamon is a key mulled wine constituent. Cinnamaldehyde, which makes up around 90% of the essential oil of cinnamon bark, is the main contributor to this flavour, and to the aroma of cinnamon. It has also previously been added to chewing gums, and research has shown it to have some antimicrobial effects.

By the way – a number of the compounds detailed here have also been featured in the 2014 Chemistry Advent Calendar. If you haven’t already, check it out here!