Since the Melakha of Borer (forbidden Shabbath labor of separating), includes all objects, anytime you have a mixture of two or more types of things, it is, as a result, always forbidden to take that which you do not want, and even that which you do want (with certain exceptions), from the mixture.
The exception is in a case where you fulfill all three of the following requirements.
1) You remove the good from the bad.
2) You use your hand and not a utensil.
3) It is done for the purpose of eating immediately.
The reason that it is permitted is when one does it in this manner, is because what he is doing, no longer appears to be the Melakha of separating, but the normal way of eating. The Posqim say that this is permitted even if you are doing it for others, provided they will be eating it right away, and that the two other two requirements have also been met.
There is a difference of opinion amongst the Posqim as to whether using cutlery is considered using a utensil and would be forbidden even to remove good from bad, or if they are considered an extension of one's hand. Some say that if the spoon, for example, is helping in the act or separating, then it is forbidden. On the other hand, if you could have done it just as well with your hand, then you are just using the spoon not to get your hands dirty, or the like, then that would be permitted.
(See Ba'al HaMaor, Kaf Hahaim oth 25. And see Teshuboth Ribbi 'Aqiba Eiger 20)
melacha, melakha, Shabbos, Shabbat, Shabbath, borer, separating, halacha, fork is extension of hand