The Howard mould count is the classic microscopic test for mould contamination in foods — particularly tomato products, where it originated. A weighed sample is prepared, spread on a Howard mould-counting slide etched with a grid, and examined under the microscope: the analyst counts the fields in which mould hyphae (filaments) exceed a defined proportion of the field. High counts indicate the raw material contained mouldy, rotten fruit — a quality and safety failing, since some moulds produce mycotoxins. Regulatory limits (such as the FDA’s defect action levels) turn the count into an enforceable standard. It is an old but telling test: you cannot hide rotten tomatoes from the microscope.