Concentrating Milk

Water is heavy, and transporting products containing it, such as milk, is costly. As a result, the dairy industry has been concentrating milk by membrane processing—reverse osmosis or ultrafiltration—and shipping it to manufacturers for use as a food ingredient. This not only reduces transportation costs, but also provides other benefits to the manufacturer.

For example, if cheesemakers in the upper Midwest are short of milk for cheesemaking, they can order this concentrate from other locations, said John C. Bruhn (530-752-2192), Specialist in Cooperative Extension in the Dept. of Food Science and Technology at the University of California–Davis. The transportation cost would be less than for unconcentrated milk, and the cheesemaker will get a higher cheese yield. The concentrate can also be used to add milk solids to ice cream or as a functional ingredient in other food products.

A relatively recent trend, Bruhn said, is to produce concentrated raw milk on the dairy farm and ship it unpasteurized for use in products that will subsequently be pasteurized. The process was approved by the Food and Drug Administration in 1996 and is being used in several states.

Concentrating raw milk at the farm, according to Phillip Tong (phone 805-756-6102), Professor in the Dairy Products Technology Center at California Polytechnic State University, San Luis Obispo, allows milk to be produced in the most economical location and shipped to where it is needed. Tong, who runs CalPoly’s annual Concentrated and Dry Dairy Ingredients Symposium (see www.calpoly.edu/~dptc), said that this can cause a big shift in where and how milk is produced, processed, and handled. However, whether the trend will continue will depend on changes in supply and demand for milk and how milk-pricing systems are set up.

North American Milk Products, based in St. Louis, Mo., is one organization that markets concentrated milk and patented systems to produce it. The organization is a partnership of T.C. Jacoby & Co., St. Louis, Mo., which handles equipment sales; Membrane Systems Specialists, Wisconsin Rapids, Wis., which developed the system; and Select Milk Producers, a New Mexico-based dairy cooperative, which bought the first five units.

According to Jacoby’s Technical Director, Bob Fassbender (phone 800-877-9556), North American Milk Products has five concentration systems in operation in Texas, New Mexico, and California. The concept, he said, was to put the unit right on the dairy farm for large producers in remote locations. As dairies develop in remote locations around country, there’s usually limited access to markets, so concentrating milk enhances the dairies’ ability to market the milk.

Because the process is a cold technology, not involving heat processing, FDA did an extensive review to make sure that concentrating the milk would not abnormally impact the bacterial load of the milk. The process starts with very clean, high-quality, Grade A milk, and the concentrated retentate must meet Grade A standards for commingled milk. The first unit was built and began commercial production in 1997 in Lake Arthur, N.M. The most recent installation was in March 2001 in Tipton, Calif.

Two systems are available. The UF system operates at 80–100 psi, the RO system at up to 500 psi. UF removes two-thirds of the water, lactose, and ash from the milk, concentrating it 3.5 times. The permeate is currently used as animal feed, although the company is exploring other ways to utilize it. Because of its smaller pore size, the RO membrane allows only water to pass through, concentrating everything else. The system is capable of separating a very clean lactose stream, without the acid damage typical of whey processing.

Unlike in conventional membrane processing, which involves recirculation, the milk flows through the serpentine membrane system in a single pass, as required by FDA. Because the milk is not pasteurized, the system is maintained below 45ºF to prevent pathogen growth. The operation of the system is straightforward. A pump feeds the system, and it essentially runs itself as long as the pressure is maintained.

The system on a dairy farm has 5–6 employees because it operates 24 hr/day. The cows are milked three times a day, so the flow of milk is ongoing. High-producing herds produce 80–90 lb of milk per cow. A small plant is about 4,000 sq ft in size, a large plant about twice that size. Small systems can process milk from 4,000 cows, and larger ones from 20,000 cows. The cost of the systems runs from $2.5 million to $5 million.

The newest thing, Fassbender said, is commercially producing a concentrated skim milk by UF. The concentrate consists of 60% protein (dry basis) and 40% other solids. It’s only been available for two months, and is receiving wide interest in the cheese industry, particularly among manufacturers of low-fat cheeses. The cheese manufacturer can use it to make reduced-fat Swiss and mozzarella cheeses. The UF skim milk is sent to the cheese plant, where it is blended to reach the desired ratio of fat and casein, then pasteurized on the way to the cheese vat. The lactose levels are reduced, and the cheesemaker doesn’t have to reconstitute a powder or get rid of excess lactose through use of culture starters, etc. The process improves the quality and functionality of the cheese and is much more efficient.

For example, he said, if a cheese plant that uses 1 million lb of milk/day replaces 10% (100,000 lb) with the concentrated skim milk, the cheese yield will be increased by about 12%. That will lower unit operating costs by up to 2¢/lb, or $1 million/yr in savings. No capital investment in equipment by the cheesemaker is needed. The dairy farmer or cooperative makes the capital investment.

The next step in the RO area, Fassbender said, is to start making beverage bases in the same facility. The fluid milk industry isn’t quite ready for RO milk yet, but some foodservice companies may be. RO milk concentrate can be used to make custom blends, which would be packaged in bag-in-boxes and pasteurized and shipped for reconstitution at foodservice outlets, such as boutique coffee shops for use as coffee creamer to replace the typical half-and-half, for example. He also sees it expanding into the soft-serve ice cream business, with specific blends tailormade for that type of application. One advantage of using raw RO milk instead of condensed milk, he said, is the flavor. Condensed milk has a slightly cooked flavor, whereas the RO milk has a very clean flavor.

As we look to the future, he said, a good-tasting, high-protein, milk-based beverage can be developed. Current “energy” beverages obtain their protein from whey protein concentrate or whey blends to achieve the desired protein levels. This often imparts a characteristic “whey” flavor to the beverage that must be masked. A custom blend of RO and UF milk provides a clean flavor. We are just scratching the surface of possible applications now, he said.

Other developments are also being pursued in dairy processing. Tong reviewed some of these.

He said that there is increasing interest in fractionation, isolation, and purification of milk components. Breakthroughs are on the horizon for new ingredients for the food industry that provide specific health benefits and/or functionality, performing better than the whole dairy product. Instead of providing broad functionality that meets lots of applications, these ingredients will be more tailored.

Work is also being conducted to extend the shelf life of dairy products from the current 2 weeks to 30–90 days, using traditional thermal methods but higher temperatures (ultrapasteurization, almost ultra-high-temperature processing), which may require use of clean-room technology in packaging the products. Some packaging innovations may have to occur, he said. Permeability and stability of the package will have to be considered. As shelf life is extended, Tong said, we may see some inherent instabilities in the products. Some of these instabilities, such as creaming (fat separation) and settling over time, are not seen with short-shelf-life products. These are all time-dependent changes that we don’t usually see in normal distribution.

The dairy industry, because of fractionation, is now producing permeates such as lactose and minerals filtered out of milk and whey and is trying to find uses for them. Lactose is the most predominant component in milk, so the industry is trying to find new uses for the permeate. In international channels, certain types of permeate may be added to other dairy ingredients, such as skim milk powder, to standardize the ratio of protein and lactose. That results in an outlet for the permeate and a more consistent skim and whole milk powder.

Another area may be a little more down the road, he said. Dairy ingredients have traditionally been made, using whey from cheesemaking as the starting point. Cheesemaking concentrates the fat and without going through coagulation and cheesemaking. Work is only at the laboratory scale as yet, he added.

Membrane processing is probably the most-used technology for separating components, he said, but ion-exchange chromatography can also be used to separate the desired components. We use it to make whey protein isolate now, and there’s no reason why we couldn’t do it with the milk stream. But if we get it out of milk, what do we do with the rest? Every time we separate milk into its components, we have to figure out a home for all those products. That’s always the challenge.

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by NEIL H. MERMELSTEIN
Editor