How would you investigate a fall in bioreactor yield?

Why

I would begin with the denominator. Are we discussing product titer in g/L, total harvested mass, purified product mass or potency-adjusted yield? Verify calibration, sample timing, dilution and material balance so an analytical artifact is not mistaken for a biological failure.

Compare viable cell concentration, culture duration, cell-specific productivity, dissolved oxygen, pH, osmolality, metabolites and nutrient feed with reference batches. If titer is normal before harvest but recovery is low afterward, inspect clarification, hold time, adsorption, filter fouling and later purification steps. If both viability and titer fall, investigate inoculum health, contamination, gases and mixing.

A single feed deviation may explain one batch, while a trend across lots may implicate materials, equipment or method drift. Document hypotheses, evidence and uncertainty, and review potential effects on attributes such as aggregation and glycosylation. In GMP settings, changes and investigations follow approved procedures.