There are two stages in preparing olives for eating:
- Getting the bitterness out of raw olives. This is generally done by either rinsing the olives in fresh water daily until the olives are edible, or by adding salt to the water and holding the olives under water for a few days / weeks until the bitterness is leeched out by the salt.
- Once they taste okay the next step is to preserve the olives in jars for eating later. The jars should contain either a simple salt brine marinade, but can also include vinegar, herbs and spices - to taste.
Yeast will form on the surface of the water at various stages - this is a light, fluffy white substance and is not harmful, so wash it off. If other colours form on the surface of the brine this could well indicate spoilage. If you add a layer of oil to float on top of the olives and brine (vegetable oil is fine) you should not get the yeast forming.