Mulled wine is the smell of wooden stalls and December markets: a red wine sweetened just enough, scented with orange, cinnamon, star anise and cloves. At home it takes half an hour, and it fills the whole kitchen with its scent.
The difference between a mulled wine that smells wonderful and one that tastes harsh comes down to a single rule: it must NEVER boil. Above roughly 80 °C (175 °F), the spices turn bitter, the citrus peel gets acrid and the wine loses its fruit. You keep it at a bare simmer, then let it infuse off the heat.
Good to know · Mulled wine is still an alcoholic drink: gentle heating does not remove all the alcohol, far from it. So it is not for children, pregnant women, or anyone driving; for them, there's the alcohol-free version with grape juice. Please drink responsibly.