Butter study focuses on maintaining flavor and texture during storage
Butter represents a significant dairy industry commodity and plays a major role in California’s economy. California is responsible for 33 percent of the 1.5 billion pounds of butter produced in the United States each year. Butter flavor and texture are critical components of consumer acceptability and marketability. While butter texture has been well characterized, the sensory perception of butter flavor had not been classified using a defined and quantifiable language. Additionally, no quantifiable information was available on how the flavor and texture of butter holds up through frozen storage, adversely affecting the marketability of frozen product. During times of surplus, butter (bulk and sticks) is often frozen to maintain shelf life and may be held at –20C for two years or longer.
The CDRF recently concluded a three-year project, led by Dr. MaryAnne Drake of North Carolina State University, to establish a quantifiable sensory language for butter flavor and texture and to characterize the flavor, texture and functional characteristics of bulk and stick butter throughout the refrigerated and frozen storage process.
The study began with a trained descriptive panel evaluating 27 commercial butters using a defined language based on the sensory characteristics that drive consumers’ preference of butter with key discriminating sensory characteristics such as color intensity and diacetyl, cooked, grassy, milkfat and salty flavors. Focus groups and quantitative consumer testing found that sensory expectations of butter vary among consumers, and butters with specific sensory characteristics could be marketed to specific target market segments.
The effects of refrigerated and frozen storage on the sensory and physical characteristics of butter were evaluated, working with quarter-pound sticks and nine-pound bulk blocks of product. Butters were placed into frozen (-20ºC) and refrigerated storage (5ºC) and were sampled after 0, 6, 12, 15, 18 and 24 months. After 6 and 12 months of frozen storage, the butters were removed and placed in refrigerated storage for 3 and 6 months with oxidative stability index (OSI) measurement and descriptive sensory analysis (texture, flavor and color) conducted every 3 months. Peroxide value (PV), free fatty acid value (FFA), fatty acid profiling, differential scanning calorimetry (DSC), vane, instrumental color and oil turbidity were determined every 6 months. Variance was analyzed to characterize the effects of storage time, temperature and package type on butter flavor, OSI, PV and FFA.
The study concluded that for optimum quality, butter quarters packaged in wax parchment paper should be refrigerated for less than 6 months. When frozen at -20C, quarters can be stored for up to 12 months. It is still advantageous for manufacturers to store butter in large blocks, which may not completely stop quality deterioration but will maintain freshly produced butter flavors (milkfat and cooked/nutty) longer. For bulk butter in refrigerated conditions, flavor quality is maintained for at least 9 months. In frozen storage, bulk butter can be stored for 18 months without flavor detriment. This estimate of the shelf life for bulk butter is conservative, since smaller (4 kg) blocks were used in the study for convenience and cost, and butter is often stored in 25 kg block form.
A final aspect of this study examined the impact of package material on butter shelf stability and if lipid oxidation was the primary source of flavor quality loss in butter. Butter quarters packaged in wax parchment paper and foil were evaluated across refrigerated and frozen storage. Both sensory and instrumental volatile analyses, in conjunction with peroxide value and oxidative stability index tests were conducted. Results indicated that while lipid oxidation occurred during storage, it was not the driving force behind flavor quality loss and that lipid oxidation tests (PV value, OSI) were not correlated with sensory flavor quality loss. Instead, absorption of volatile organic components from the package and refrigeration or frozen storage unit were the primary source of flavor quality loss. Butter quarters packaged in foil or thick wax parchment wrappers, as a result, will maintain freshness longer than butter wrapped in thinner wax parchment paper.
In addition to surplus years, maintaining quality during storage is becoming increasingly important as export markets expand. Exports of butter and milkfat totaled 92.8 million pounds during the first five months of 2008, compared with 14.2 million pounds during the same
period in 2007. Since butter is a highly prized fat source in terms of flavor and textural properties, it is important that manufacturers understand how long their product can be stored before negative attributes develop. These off-flavors could potentially carry-through to applications and negatively impact consumer perception.
