Preserve any herb or spice in oil and you run the risk of paralysing those who consume it with a severe case of food poisoning, known as botulism. As the legendary Harold McGee puts it, in his authoritative tome On Food and Cooking, "Oils encourage the growth of deadly Clostridium botulinum, whose spores can survive brief boiling and germinate when protected from the air." This put the fear of God in me. Clearly, some careful research was in order.
I won't bore you with the details, just summarise my findings:
- Gently heating the oil helps eliminate bacteria.
- Don't use fresh chillies if you want to keep it for longer than a week.
- Use a light olive oil. There's no point splurging on fancy extra virgin: its flavour will be overwhelmed by that of the chilli.
- Sterilise the bottles you intend to store the oil in.
- Boil the whole dried ingredients in malt vinegar before adding them to the oil, to help eliminate any lingering bacteria.
- Shake the flavoured oil, once bottled, to get rid of trapped air bubbles.
- Don't add garlic to your chilli oil, as garlic provides enough nutrients for botulism to grow.
1 pint malt vinegar
2 cups olive oil
2 tsp crushed dried chillies
4 whole dried chillies (I bought mine - variety unnamed - at the local Chinese supermarket)
Sterilise the bottle(s). I wash mine in hot soapy water, then place them in a cool oven (tops removed if they have rubber seals), turn the oven to 150C and leave the bottles for 20 mins. Remove carefully, ensure they are completely dry, and set aside.
Boil the whole dried chillies in malt vinegar, fully submerged, for 10 mins. Drain on kitchen paper. Open the windows - boiling vinegar stinks! Those of you familiar with chutney-making will know what I'm talking about.
Place the olive oil in a saucepan over a low heat, and add the crushed and whole dried chillies. Warm through for 5 minutes (do not boil), remove from the heat, and leave to cool before bottling.
The longer you keep it, the hotter it will get. If you don't want it to get any hotter, after testing it a couple of weeks after making, strain out the chillies and re-bottle.
Store in a cool, dark place.