Refrigerated and frozen storage impact butter flavor, texture.

Butter is often stored refrigerated or frozen for extended periods of time because supply and demand for the product fluctuates. Manufacturers must know when the flavor and texture of their butter begin to deteriorate so that they can deliver a high-quality product.

Scientists at North Carolina State University and elsewhere characterized the effects of refrigerated and frozen storage on the sensory and physical characteristics of butter. They found that bulk butter may be refrigerated for up to nine months, while the storage of stick butter should be limited to six months. Frozen butter may be stored for almost a year before evidence of deterioration is detectable.

Fresh butter was obtained on two occasions from two facilities in 114-g sticks and 4-kg blocks. The researchers placed the butters in both frozen (-20 C) and refrigerated (5 C) storage. The frozen butters were sampled after 0-, 6- and 12-month intervals. The refrigerated butters were sampled after 0, 3, 6, 9, 12 and 15 months.

After six and 12 months of frozen storage, a portion of the butters was removed and placed in refrigerated storage for three and six months. At each sample time, scientists determined the products' oxidative stability index (OSI), peroxide value (PV), free fatty acid value (FFA) and fatty acid profile. They also undertook a descriptive sensory analysis of texture, flavor and color.

The investigators conducted an analysis of variance to characterize the effects of storage time, temperature and package type on product quality. They found that the storage time, temperature and the type of packaging system affected butter flavor, OSI, PV and FFA. The refrigerated stick butter developed refrigerator and stale off-flavors concurrent with an increased indication of oil oxidation--lower OSI, higher PV and FFA--within six months.

Off-flavors and oil oxidation were not evident in the bulk refrigerated butter until nine months. At six months, the frozen butter was not different than the fresh butter, but after 12 months, low levels of-off flavors were evident.

Further information. MaryAnne Drake, Department of Food Science, North Carolina State University, 236-E Schaub Hall, Raleigh, NC 27695; phone: [phone]; fax: [phone]; email: [e-mail].