Optimizing a yarn production process with respect to foreign materials

The invention relates to a method for optimizing a yarn production process in which foreign materials (90) are monitored in a textile fiber formation (9). The textile fiber formation (9) is illuminated with electromagnetic radiation from at least two color ranges. The foreign materials (90) are classified into different color classes according to their colors. If a sufficiently large random sample with classified foreign materials (90) is available, a frequency distribution of the foreign materials is determined for the color classes and compared with a reference frequency distribution. If the determined frequency distribution deviates from the reference frequency distribution, at least one of a set of multiple optimization actions is performed, e.g., a warning signal is output.