Chilli vinegar is ready for use immediately after preparation, but it will get stronger and get better taste over a few days as capsaicin responsible for the hot taste dissolves in vinegar. Optionally you can use green chillies, but the colour will turn green-brown. My favourite chillies for that recipe are really hot tiny bird chillies. When chopping peppers, you can remove the seeds if you don't like them. This will make the vinegar slightly milder. Chilli vinegar is perfect for sauces, soups, pastas and casseroles. Adds spiciness ;-) and turns up the taste of the dish.