There are two methods; the first gives the best results as it allows the full ﬂavours of the spices to be absorbed by the vinegar, but the second method is quick.
For the first method, put the sugar, celery seeds, mustard seeds, cardamom pods, cloves, coriander seeds, allspice berries and chillies in a bowl. Lightly crush the black peppercorns, peel and thinly slice the ginger and add them, with the garlic, to the bowl. Mix the spices together well, then put them in one or two clean, dry bottles and fill to the top with the vinegar. Seal and leave to stand for one to two months, shaking occasionally. Strain the vinegar before using.
For the second method, put all the ingredients in a bowl, cover with a plate and stand the bowl over a saucepan of water. Bring the water to the boil, remove the pan from the heat and leave the bowl over the pan for up to two hours, allowing the spices to steep in the warm vinegar. Strain, pour into a clean bottle and use within a short time.