American consumers have become accustomed to the luxury of fresh, refrigerated milk as a mainstay in their consumption habits. But that luxury is slowly eroding, as dairy plant consolida­tions are altering distribution and mass-merchandiser venues operate through strategies of non-refrigerated retailing.

The result is that dairy beverages that can be stored at ambient temperatures and have extended shelf life are becoming top of mind for dairy manufacturers. But these dairy products can suffer from off-flavor notes and stability issues. So while the prospect of shelf-stable dairy products and non-refrigerated distribution are at the forefront of the industry, the problems that plague dairy products treated with high heat remain an obstacle that dairy manufacturers and food scientists are struggling to overcome.

“The science is progressing and the industry is perfecting the existing processing technologies of extended-shelf-life products. It is an industry learning curve and the quality is continuing to get better on these products,” says Bill Haines, vice president of innovation at Dairy Management Inc. (DMI), Rosemont, Ill. “University studies and dairy plants are fine tuning the processes to achieve the best products. And on the flip side, consumer tastes and perceptions will shift and adapt over time, so as these products become more common, what was perceived as a shortcoming will become more mainstream.”

Standard dairy milk products undergo HTST pasteurization to render them safe for human consumption and reduce bacterial populations, yet these dairy products still must be refrigerated. Such “fresh” milk products have a shelf life of 14 to 21 days. Many milk products today utilize HTST pasteurization coupled with hygienic packaging processes to extend shelf life to 30 days or more.

Other options for extending the shelf life of dairy products require higher heat treatments coupled with hygienic packaging. For example, ultra-pasteurized (UP) products are thermally processed at 280 degrees F for two seconds and, if stored refrigerated, these dairy products have a shelf life of up to 45 days.

Even better, if UP dairy products are hygienically packaged using aseptic technology, these products can be shipped and stored at refrigerated temperatures and offer a shelf life of up to three months. However, UP temperatures are the conditions under which the taste as well as the stability of milk beverages can begin to degrade. Some UP dairy products can suffer from slight “cooked” notes, or can have the milkfat components separate out over time during storage.

Another possible higher-heat treatment is ultra-high-temperature processing (UHT), which heats milk products for four to 15 seconds at 280 to 302 degrees. If UHT products are aseptically packaged or retort processed, the milk products can be shipped and stored at ambient temperatures and can offer a shelf life of six months to a year. However, these extreme amounts of heat can result in the disadvantageous off-flavors and stability issues that consumers find unacceptable.

The currents of today’s changing dairy world demonstrate the need for finding a solution to these problems. Many dairy processors and university dairy science programs are studying ways to improve the sensory or textural characteristics of high heat treated dairy products.

Dairy manufacturers realize that consumers are not ready to transition completely to shelf-stable fluid-milk beverages. Nonetheless, simply out of necessity, there is some movement toward these types of products.

“In dairy, Europe has always been way ahead of America. And what we see in Europe and in other countries is that shelf-stable, aseptically packaged dairy products have been the standard for a long time,” says Jan Kuiper, executive vice president at Stork Food and Dairy Systems Inc., Gainesville, Ga. “Extended-shelf-life products are based on economics, and the United States is just beginning to experience the small dairy cooperatives and small plants failing to survive. As we see a concentration of dairy plants in one central location, the resulting distribution issues will force a change to extended-shelf-life products.”

Another factor influencing the growing need for ESL dairy products is the growing popularity of mass merchandisers.

“Consumers are buying milk products outside of the traditional grocery store — in club stores, dollar stores and mass merchandisers. These channels are not around the corner from the local dairy and in many cases the supply chain is quite a bit longer, so aseptic-packaged ESL products are critical,” says Jeff Keller, vice president of strategic business development at Tetra Pak Inc., Vernon Hills, Ill.  “There is a very fixed amount of chilled retail space in these channels and so ESL dairy products are a wonderful solution for them.”

While there may be a limit upon how willingly American consumers will embrace unflavored fluid milk that is not refrigerated, new innovative dairy beverages that do offer an extended shelf life are currently making waves in the market.

One of the biggest success stories in extended-shelf-life dairy products is the introduction of Horizon Organic’s single-serve, aseptic, flavored-milk products. This product is noteworthy because the line met the needs of the intended audience, but also happened upon an unintended and lucrative niche.

“Horizon single-serve, aseptically packaged milks in the Tetra Prisma package have been a tremendous success in a number of different areas. But the most interesting success has been the solution they offered to Starbucks,” says Keller. “Most Starbucks don’t have extra refrigerated storage, but these products can be stored at ambient temperatures and then placed in the small cooler out front as needed.”

Three years ago, Horizon introduced three varieties of flavored, single-serve milk products in TetraPrisma packs. The TetraPrisma pack is a slim 8-ounce package with an outer foil wrapper — seen as more “adult” than a juice box.

This product line can be shipped and stored without refrigeration, although most retailers sell the products in the refrigerated case.

“It is common everywhere else in the world to have six months to nine months to a year for the shelf life of a dairy product that has been packaged aseptically,” says Keller. “And with flavored milk that is packaged aseptically and has been on the shelf for nine months, if you chill it down and conduct a blind taste test, the untrained consumer could not tell the difference between that product and a fresh milk product.”

The Horizon Organic single-serve milk product line was also a success in natural food channels where it was sold both on the shelf and in the refrigerated case.

And finally, the ability of Horizon’s single-serve aseptic milks to be stored at ambient temperatures brought the product into club stores.

“Aseptic processing is the highest grade of hygienic filling, and together with the UHT process creates a sterile milk product with an extended shelf life,” says Kuiper. “We make an aseptic filler that delivers 60 to 90 days extended shelf life without refrigeration.”

It seems that one of the keys to successful marketing of shelf-stable fluid-milk products is education. The single-serve milks from Horizon Organic may be so popular because the consumer audience for these products is generally more educated about their food.

In fact, if extended-shelf-life dairy products are going to be embraced by consumers readily, an extensive education campaign must accompany the new products to market, since unfamiliar means of consuming milk will not be easy for consumers to swallow.

The other inroad in extended-shelf-life dairy beverages is in value-added dairy-based products.

“The UHT process results in a different taste than fresh milk, and the American taste hasn’t adapted to it yet. But a lot of new product activity in dairy extended shelf life includes the flavored products or value-added dairy products, in which the consumer doesn’t taste that sterilization effect,” says Kuiper. “Eventually, shelf stability will prevail, which is why our business philosophy is going that direction.”

Kuiper points to rising energy costs being another factor propelling extended-shelf-life dairy-based products, as the energy needed to ship and store refrigerated products will become more costly.

“The dairy category represents a category with untapped potential for non-traditional processors, like the beverage companies who are hearing about current consumer interest in health and wellness,” says Haines.

The soda companies coming under fire for products with “empty calories” might soon become competition for dairy manufacturers. Such companies have established massive distribution systems that could easily incorporate ESL dairy-based beverages.

Of course, working with dairy components in a beverage product is far from simple. Just ask Dr. Phil Tong, professor of dairy products technology at California Polytechnic University in San Luis Obispo, Calif.

Tong is studying heat-induced changes that can affect stability issues in various product applications, through funding from DMI and a matching grant from the California State University Agricultural Research Initiative. Tong’s project aims to understand and ultimately improve the applicability of dried dairy ingredients in formulations to create dairy-based beverages.

“We are trying to understand what contributes to the variability of dried dairy ingredient properties and systematically study those variations and their effects upon the stability of the beverage system,” says Tong. “There are subtle differences in dried dairy ingredient ratios of casein to whey proteins, which may contribute to differences in their behavior in the presence of heat.”

Whey proteins tend to denature from heat, unfold and create opportunities for new ingredient interactions to take place in these systems. This causes whey proteins to gel or coagulate when they are heated. Caseins, on the other hand, usually remain stable under very high heat processing at the pH of milk.

Tong notes that additional components of a typical dairy-based beverage environment — such as acid — also affect stability. For example, the acid from a fruit juice results in a pH of 3.5 or 4, at which point casein can become less stable. Although some whey proteins are more stable at this pH, the presence of acid can result in an unpleasant chalky mouthfeel if not addressed properly. Typically such dairy-based beverages must incorporate buffers and polysaccharide gums or other stabilizers to reduce these undesired effects.

Acid environments can limit the amount of dairy proteins that can be utilized in such environments. In addition, the impact of acid environments may depend on the ratio of these dairy proteins to other constituents.

“The other ratio we will vary and study in the milk powder is the ratio of solids to protein, or lactose to protein or protein to minerals,” says Tong.

When the protein level in milk powder is high, stability becomes a challenge if this is not addressed.

“In the United States, we don’t control the protein content of milk when we create milk powder; we simply remove the fat out of fresh raw milk, pasteurize it and remove the water to dry it. So whatever ratio of constituents are inherent in the original milk will be the ratio of the final dried product,” says Tong. “But now there is technology available to adjust the ratio of protein to lactose through membrane processing. So another part of our project will document how varying the composition of protein to lactose affects the stability of the system.”

This is the first phase of the project. Then starts phase two, wherein Tong will begin to study some of the commercial blends of stabilizer and chelating agents that help improve stability in these dairy-based beverage systems.

“Carrageenans are already present in many dairy beverage products to stabilize the system, but they are becoming critical in ESL products that are ambient-stored,” says Ted Benic, director of technical services and general manager of dairy blended systems at TIC Gums, Belcamp, Md. “As these products warm up, their viscosity drops and they rely upon some sort of suspending agent to keep the product solids in suspension.”

Many of the value-added dairy-based beverage products contain vitamins and minerals, and 75 to 80 percent of these nutrients are insoluble in a water or milk-derived environment, tending to settle out of solution.

“The trend is to have more vitamins and minerals. Ten percent of the RDA doesn’t cut it anymore, now we want 100 percent of the RDA in a serving,” says Benic. “This means adding five to 10 times the normal amount of vitamins and minerals that would exist naturally in a product, and trying to get all of this in one product and keep them suspended.”

Carageenan also reacts with potassium, calcium and sodium, which can be an advantage in keeping the emulsion if this effect is accounted for in the formulation. A gelatinous mass can result if high levels of potassium, calcium or sodium are included with carageenan without an understanding of this synergistic effect. Sometimes sequestering agents are used in these formulations to bind some of the calcium, sodium or potassium to control their reaction with carageenan.

“Lecithin is used as an emulsifier to bind fats in dairy-based beverages, eliminating the lines of separation we see in products,” says Benic. “These are called ‘multi-phase’ products, where we are trying to get water and oil to bind together. After these products are on the shelf for six months the interfacial tension starts causing the emulsion to break unless lecithin is included.”

If more than 0.1 percent lecithin is used in a product, consumers notice an off taste, so levels of the ingredient must be kept circumspect. And depending upon the desired foaming effects, lecithin can be used in conjunction with mono and diglycerides (to yield more foaming), although these ingredients are not considered natural and sometimes are label-prohibitive.

For now, consumers are most willing to embrace extended-shelf-life dairy products that are familiar — meaning refrigerated. HP Hood LLC, Chelsea, Mass., may be the reigning expert in this arena. HP Hood has been manufacturing refrigerated extended-shelf-life dairy beverages for several years, including products within the company’s licensed brands such as Lactaid, Nesquik and Coffee-Mate.

“Our extended-shelf-life products all deliver at least 60 days shelf life. These products undergo higher-temperature short-time treatment and are filled under environmentally controlled systems,” says Peggy Poole, Hood’s vice president of quality. “This filling environment is commercially sterile, with fillers that have been hyper filtered, air that is hyper filtered and packaging materials that have been treated to ensure sterility.”

And just in November, Hood began processing and distributing Stonyfield Farm-branded organic milk as a new extended-shelf-life product. This new development is generating a lot of excitement.

“The reality is that we must stay in touch with our consumers and their changing needs,” says Poole. “That means we continue to monitor consumer needs so we can respond to changing demographics and nutritional demands by developing new formulas and introducing new, innovative products.”