Tania Sanchez: Fight germs: eat mince pies

In the month leading up to the 25th of December, a woman who lived the first half of her life in tropical Saigon – and who happens to be my mother – will drag a purchased fir tree into her cosy California home, where winter weather means a millimetre of morning frost on the windows that disappears by 9am.

With that alpine fragrance bracing her spirit, she will fill the house with smells of clove and cooking sugar, and bake enough gingerbread to construct a vast edible metropolis, its masonry mortared with white frosting and inhabited by two-dimensional biscuit men, whose homes she will buttress with red-and-white peppermint canes and bejewel with gummy fruits.

She will fumigate the bathrooms with the hissing spittle of some red-topped limited-edition aerosol can covered in pictures of holly, which will reek of cinnamon, apple, and evergreen forest, or worse, an eggnog sludge of synthetic vanilla and nutmeg, or maybe that wonderful fruity-clove-menthol thing they call bayberry when they're not calling it wax myrtle. It is the soul of Christmas, the one odour that belongs solely to Christmas, not because of anything to do with Christ, but because they make candles out of the berries' wax, and Christmas is about candles. That is because at Christmas, every Christianised household, regardless of climate and technological progress, becomes medieval Germany in deepest winter. Below the equator, Argentinian households enjoying the roasting glare of summer watch their living-room pines, exhausted after their long descent from the Andes, helplessly, leprously shed their luxuriant needles by the armful. Children in swimsuits tweak bells attached to artificial mistletoe. Plastic reindeer go soft in the noon sun. For a month the house must be made to breathe the air of a Saxon winter, brought by Spanish missionaries.

These peculiar scents, so season-specific that many candles fragranced with some permutation of evergreen, fruit and spice are merely labelled "Christmas" with no further explanation, make up a standard suite of sensations with origins all over Europe, but crystallised into their current, apparently unalterable fossilised form in the romantic 19th century, when German Prince Albert set his Tannenbaum up in England, and on both sides of the Atlantic, everyone who was anyone set out with a hatchet for a vital bit of holiday décor.

These pagan pongs of puddings and pines are naturally nothing to do with the precious perfume resins – frankincense and myrrh – given to the infant Christ by the Oriental kings, who had different ideas of what to give a baby than we do. Now the standard conical Christmas tree, scaled to a normal ceiling, is perhaps the largest home fragrance diffuser in existence. Its hale, stirring odour not only smells clean, it is cleansing, since pine oil is a powerful bacteriostatic, good for the tree fending off micro-invaders, and good for the household detergents that include it.

In fact, as we look harder at what seemed the traditional smells of Christmas, their affinity for each other begins to seem not so arbitrary at all. A secret something links the aromatic riches of the table with the greenery festooning the room: an invisible and constant battle against germs. As my mother dances through the halls blasting cinnamon, clove, nutmeg, ginger, plum and caramel through every doorway, as if to run off some invisible devil with a hatred for pastry, she has no idea she is scenting the place like one gigantic mincemeat pie or Christmas pudding, for she has never seen a Christmas pudding and wouldn't know whether to eat it or shoot it if she did.

These dense, dark cannonballs of long-cooked sugar and treacle, dried fruit and spice didn't start life as holiday sweets. The word mincemeat reveals all: these dishes have their origin in the preservation of meat in the days before refrigeration, say the 15th century, when animals slaughtered in autumn were macerated in this archaic chutney, made hostile to bacteria with an enormous dose of sugar and salt, stuffed with currants and plums, spiced, and left to hang in mummified glory, to nourish people through the long starved winter. Those delicious mulling spices are death to bacteria: for instance, the molecule known as eugenol, the main component of clove oil, and the molecule cinnamaldehyde, ditto in cinnamon, are both enthusiastic enemies of nasty bacteria such as listeria, staph and e.coli. And what bacteria hate, we love instinctively; we have kept the spice and sugar and now we put the meat in the fridge.

'Perfumes: the Guide', by Luca Turin and Tania Sanchez, is published by Profile