I've made a chili sauce mainly with fresh chili, herbs and spices and olive oil & small bit of balsamic vinegar, I've sealed it tightly in a PRESERVE bottle mainly used for making jam, but it seem to be bubbling after a few days?what could be the problem
You are lucky - your sauce is spoiling and you are seeing it.
It is not safe to can random recipes, or to store them (uncanned) for more than 5 days in the refrigerator or more than 2 hours at room temperature. This means that, if you go ahead and can them neverthelss, you get one of the outcomes:
- no pathogenic bacterial growth and no symptoms of spoilage.
- no pathogenic bacterial growth, but symptoms of spoilage (caused by harmless bacteria or yeasts)
- pathogenic bacterial growth and no symptoms of spoilage
- pathogenic bacterial growth and symptoms of spolage.
Many people try it out, get outcome 1 (which is really frequent) and conclude that it is safe and outcomes 2, 3 or 4 will never happen. They are wrong.
What happened to you is either 2 or 4, because the bubbles are caused by bacteria digesting your sauce and creating gasses as a byproduct of their metabolism. There is no way to tell if the bacteria are harmless or pathogenic. So your food is spoiled.
The reason I said "lucky": You also narrowly missed case 3, which is the most dangerous. Then you would have been at real risk to get seriously ill, without any warning.