A review of international standards and the scientific literature on farm milk bulk-tank sampling protocols

Adequate agitation is required to ensure homogeneity before sampling from on-farm bulk tanks, but excessive agitation may cause churning with a resulting loss of milk quality. Homogeneity can be assured by thorough mixing before a sample is taken and can also be combined with intermittent agitation of the bulk tank. There is general but qualified agreement among various countries and agencies, such as the IDF, that 5 min of agitation for small, and 10 min for large, quiescent farm-milk bulk tanks is required to ensure sample homogeneity. However, no empirical studies are cited to support these standards. The few studies that examined bulk-tank mixing estimate required agitation times of 8 to 10 min or longer, depending on the size of the tank. If intermittent agitation is practiced, mixing for 1 to 2 min before sampling is considered acceptable in some jurisdictions but, once again, empirical supporting evidence is absent. Automatic samplers decrease the amount of time needed to obtain a sample from the bulk tank, but both intermittent agitation and agitation during milk transfer are still recommended to minimize fat residue accumulation in the bulk tank. Systematic studies are needed to establish mixing protocols that assure accurate sampling for all tanks in a given jurisdiction.