With cooler winter temperatures it is very common for Olive Oils to develop a cloudy appearance. This is completely natural and nothing to be alarmed about. Like other vegetable oils, Olive Oil is liquid at room temperature, but if cooled sufficiently it will eventually turn solid. For Olive Oils this process starts to happen once the temperature drops below 10°C, and the first sign is cloudiness. Often, one batch will be affected, while another remains perfectly clear. Or, one batch may become turbid, while another develops tiny globules.
The way that a batch of Olive Oil responds to cold temperatures depends on the varieties of olives and their proportions in that batch, which region the olives were grown in, climatic conditions during growth, ripeness at the time of harvest, etc. All of these affect the composition of the oil and its response to cool temperatures. Cloudiness can usually be reversed by warming the oil gently. However, there is no need to do this, as the cloudiness does not affect the flavour or the underlying quality of the oil. In fact some people recommend refrigerating olive oil and using it as an alternative to margarine or butter.