Every dairy farmer knows that high-quality, pleasant-tasting milk can’t come from unhealthy cows. Keeping cows healthy is the first, best step toward milk with a sweet, clean taste. Having healthy cows with low somatic cell counts goes a long way to avoiding milk with a foul aftertaste, off-flavors or unpleasant odors.

The American Dairy Science Association (ADSA) has guidelines for the sensory evaluation of milk. On this scale, milk is evaluated for the existence of “flavor criticisms,” which range from acid, astringent and bitter to unclean, salty and rancid. The presence of any flavor criticism is rated as slight, definite or pronounced.

Those off-flavors considered most unacceptable are penalized more than those with less impact. For example, milk with a pronounced “feed” taste receives less penalties than a sample with a slight rancid flavor profile would.

Processors often penalize farmers for high somatic cell or bacterial counts, both of which lead to milk flavor concerns. High somatic cell counts cause milk to feel watery, while bacteria generate an unclean taste.

While these issues are important ones, they aren’t the only reasons milk from your bulk tank might not be rewarded a high score for taste. Even if your numbers are good, your milk’s flavor might not be.

Mixing and mingling milk

Processors are very aware of factors that will influence the final taste of their products, beginning at the farm and ending with consumption. The commingling of milk from many farms, combined with flavor impacts that occur during storage and processing, tend to neutralize many off-flavors coming from any given bulk tank.

“One of the biggest ways that processing ‘fixes’ off flavors is by commingling milk from different farms and different milk trucks,” says Michael Gould, food technologist with WhiteWave Foods.

“As they say, ‘The solution to pollution is dilution,’ and it holds true here. If one farm has slightly off-flavored milk, by the time it is mixed with the milk from other farms on the milk truck, and even to a larger extent at the dairy plant,” it is no longer noticeable.

In a recently reported study by the University of California – Davis, raw milk from tanker trucks headed to large processing plants was genetically sequenced. The results demonstrated seasonal changes and highly diversified bacterial populations in the milk while in the tanker truck environment.

The study also found that the large silos at the processing plants contributed their own bacterial profiles to the commingled tanker loads stored there.

According to the report: “Remarkably, the effects of the processing facility outweighed those of the raw milk microbiome, and the microbial composition changed distinctly within some but not all silos within a short time after transfer.

This knowledge can be used to inform cleaning and sanitation procedures as well as to enable predictions of the microbial communities in raw milk that result in either high-quality or defective products.”

“From a plant perspective, there are definite sensory effects which can be based on: pasteurization method – low temperature vat, high-temperature/short time or ultrahigh temperature processing; breed of cow; homogenization; as well as plant cleanliness and chemical contamination that can occur at the plant,” Gould says.

“Another cause of off-flavors in milk is transparent plastic packaging. An even bigger issue is stores switching from fluorescent lighting in the dairy case to LED lighting. Opaque packaging completely eliminates light-oxidized flavors.”

Flavor factors

It’s common industry practice to categorize problems with milk flavor by whether they are absorbed or transmitted, bacterial or chemical in nature. All three categories can arise at any stage of the game: on the farm, in storage or during processing or distribution. And some off-flavors can arise from more than one root cause.

Absorbed or transmitted issues move through the cow’s mouth or nose to the bloodstream and into the milk. When cows eat feed with a strong flavor, such as onion or garlic, or a strong barn flavor, it is transmitted to the milk in the udder. Or these issues may arise after the milk leaves the udder, during storage.

Common issues are milk storage under conditions of poor ventilation or flavors absorbed due to poorly cleaned refrigerators. Stale, unclean or “feedy” odors often originate in this manner.

Bacterial issues cause putrid, rancy, fruity, malty, bitter or unclean tastes and are the result of microbial contamination. This can occur at any time during the milk supply chain, from cow to consumer. The time it takes for the milk to spoil depends on the microbes present as well as the level of contamination, and processing and storage parameters.

Chemical reasons for off-flavor can arise within the cow or after milking. Cows with ketosis generate a “cowy” flavor to milk. Stress or illness can break the membranes of milkfat globules, causing a rancid flavor. Chemical contamination of the milk, or exposure to metals or oxidizing factors such as various light sources during storage, are other chemical causes of off-flavors.

Farm factor

Although the commingling of milk at large processing plants can neutralize or alter flavor issues arising on the farm, that doesn’t mean dairy farmers shouldn’t be aware of the taste of their milk.

Many factors at the farm or herd level can and do cause milk flavor issues, and being cognizant of how and when these issues occur, and taking preventative measures, can keep milk from your bulk tank tasting its best.

The cow itself, the feed it consumes and the farm environment all contribute to the taste of the milk leaving the udder.

Heredity, breed, stage of lactation and number of lactations all alter the taste of milk from any given cow. Combine these with feed and water, barn environment and cow health, as well as processing methods, and the opportunity arises to find a unique flavor profile, based on controlling these myriad factors. The variables, even before the milk leaves the udder, are many.

Researchers at Virginia Tech have recently found that too much iron in the cow’s drinking water can alter the taste of milk due to the degradation of proteins, as well as the oxidation of fats. Lack of vitamin E in the diet can cause oxidized or metallic flavors, too, as can too much dietary fat.

“Often, on-farm processors promote specific characteristics of their milk, creating a ‘signature taste.’ Examples of this might include being grass-fed, single-breed, pastured cows or silage-free. There are differences between breeds in protein and fat that have an effect on the finished product flavor, particularly for fluid milk,” Gould says.

“There are seasonal changes with milk flavor, particularly with feed changes – pasture versus silage versus dry hay – as well as changes in milk composition.” These changes can be reflected in the taste of the milk.

Milk flavor also undergoes alteration every step of the way after leaving the udder, no matter where it gets processed. But when it’s processed directly on the farm, from a single herd, there is no margin for error.

“For on-farm processing, farmers need to pay attention to all of the management steps because there may not be an opportunity to dilute their milk with another supply of milk if something is wrong,” Gould says. On the farm, “feed, parlor cleanliness or equipment use and maintenance,” are the three areas where problems can arise, altering the milk flavor profile and potentially causing off-flavors.

The basics of great-tasting milk begin with healthy cows – quality feed, clean barns, sanitized equipment without chemical residues – and packaging that prevents environmentally caused changes.  

Tamara Scully, a freelance writer based in northwestern New Jersey, specializes in agricultural and food system topics.

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