CORVALLIS, Ore. — Raw milk quality isn’t compromised when tanker trucks sit empty and uncleaned for hours between loads, according to new research at Oregon State University.
The findings, published in the Journal of Dairy Science, could inform updates to the Grade “A” Pasteurized Milk Ordinance, said Lisbeth Goddik, professor and Extension specialist in dairy processing in OSU’s College of Agricultural Sciences.
The ordinance — a set of minimum FDA standards for producing, processing and packaging Grade A milk — allows tankers to be used repeatedly for 24 hours before mandatory cleaning. However, it does not specify how long a tanker can remain empty between loads.
OSU researchers have studied raw milk quality and long-distance milk hauling for several years. In 2015, they published results showing that “clean-in-place” sanitation practices mitigate any measurable effects on milk quality.
Study focused on idle time between loads
In the latest study, Goddik, OSU microbiologist Joy Waite-Cusic and graduate student Eva Kuhn focused on how long tankers can sit empty. The research was funded by Dairy Management Inc.
“These trucks go out up to 10 times each day and often sit empty between loads,” Goddik said. “As soon as the raw milk is emptied, air comes into the tank and the truck immediately begins warming up. We believed there would be a build-up of bacteria on the surface inside these trucks.”
All milk is safe for consumption because it’s pasteurized. However, milk quality — such as taste — can be affected by enzymes that survive pasteurization.
“This can produce off-tasting milk, for example,” Waite-Cusic said.
Simulating worst-case conditions
To simulate worst-case conditions, the researchers used five-gallon milk cans left empty and dirty between loads — especially in warm weather. They then tested milk samples to detect bacteria levels associated with raw milk quality.
The pilot study indicated that extended idle periods could degrade raw milk quality. So the team scaled up the study in collaboration with a major Pacific Northwest dairy cooperative.
The full-scale study followed a commercial tanker that first collected milk from a farm known for lower raw milk quality. The tanker then sat idle and uncleaned before picking up milk from a farm with superior quality.
Kuhn collected milk samples from each farm’s bulk tank and again from the tanker before unloading. The results showed that idle times of up to six hours — common in U.S. milk hauling — did not significantly compromise milk quality.
“Current industry sanitation strategies are working,” Waite-Cusic said.
Second study highlights sanitation gaps
The research team also published a second study in the Journal of Dairy Science focused on broader milk-hauling sanitation practices in the western United States. That study found that manual cleaning procedures are a potential weak point.
“Automated cleaning procedures work, but every time there is a human involved, things don’t always go as they should,” Goddik said. “We observed that some workers don’t clean as well as others. That needs more attention.”
Previously titled Idle, uncleaned milk trucks don't compromise the quality of raw milk, OSU study shows
