There are precipitates in the fetal bovine serum, is this bad?

In almost every instance, the serum is NOT contaminated. Occasionally thawed serum will appear cloudy. It is usually the result of normal serum components. Fibrin (a non-globular protein involved in the clotting of blood) is most common. Fibrin appears in small quantities as a fine flake or may occur as a lump of a semi-solid substance. The presence of this material does not alter the serum’s performance and may be mistaken for microbial contamination. If the turbidity is a concern, it can be removed by filtration through a 0.45µm filter. However, the sediment may clog many lab-scale filters. If necessary, allow the serum to stand. The sediments will eventually fall to the bottom of the bottle and the serum can be decanted.