It is very hard to distinguish biased from opinions, but generally former refers to a strongly expressed opinions while latter refers to just simple subjective expressions. However, when we think about it down to deep , we realize that there is a major problem distinguishing one from another.
Personally, I would say biased and opinions are basically not possible to be completely differentiated. Biased and opinions both are subjective expressions that always include personal opinions which are always biased to a degree. However, we can see that there must be some sort of difference between biased and opinions, because obviously some expressions such as ‘I like grapes’ are simply preferences. It is impossible to definitely differentiate biased and opinions other than spotting significant characteristics from each concept due to the imperfection in language itself. I think one indicator that can distinguish them is the intensity of personal expression over other’s view. Strongly biased opinions tend to disregard other possible point of view. This is especially in case where the statement regards controversial issues. So, bias is more like when one’s strong preference interferes others view point. Rather than distinguishing bias and opinions, I think its much better to see it as each end of spectrum, the more strong personal expression will shift it toward bias, and weak ones will be shifted toward opinions. Though, even simple preferences can be biased to a degree, so it is not possible to completely distinguish opinions from bias