You have to be careful when preserving vegetables such as capsicums, mushrooms, ginger and garlic in oil. They can be preserved in oil as long as the final pH of the mixture is below 4.6, which will ensure that pathogenic bacteria doesn't grow. Domestic vinegar contains four percent acetic acid.
This will not guarantee that the products will not spoil if not kept properly refrigerated, but it will ensure that they do not become toxic.
For further information contact the CSIRO (http://www.csiro.au) for a fact sheet Preservation of Vegetables in Oil and Vinegar. Below is our recipe which was approved by the CSIRO.
Grilled preserved capsicums and olives (makes about four cups)
4 red capsicums
4 yellow capsicums
300g black olives
2 cloves garlic, crushed
4 cloves garlic, halved
Salt and black pepper to taste
2 cups white vinegar
4 to 5 cups light olive oil
1. Cut capsicums into quarters, remove seeds and cores. Place capsicums on an oven tray, skin-side up, cook under a hot grill until skins blister and begin to darken; cool slightly. Place in a plastic bag, seal; stand for 30 minutes.
2. Remove skins from capsicums. Cut lengthways into 2cm thick strips. Place capsicums in a bowl with olives and garlic; season with salt and pepper.
3. Place vinegar in a pan, cook until 85C, a little below boiling point. Stir into capsicum mixture, stand for five minutes; drain.
4. Place capsicum mixture in hot, sterilised jars. Pour in enough hot oil to cover ingredients; seal while hot; cool. Refrigerate for up to two months or until required. Refrigerate after opening.