Why is residue testing done after equipment cleaning in bioprocessing?

Correct answer: To check whether previous material remains

Residue testing verifies whether cleaning has removed material from the previous operation. The residue may be product, raw material, cleaning agent, microbial cells, or another process substance. If it remains and enters the next batch, it can cause cross-contamination, alter composition, interfere with testing, or create a safety and regulatory failure. The test therefore supports cleaning validation and batch-to-batch control. Option A is correct because it directly states that the purpose is to detect remaining previous material. Making the fermenter larger, burning the medium, or naming the product is unrelated to post-cleaning verification, so B, C, and D are wrong.