Saturday, May 25, 2013

The shelf-life of bee honey


Honey stored in sealed containers can remain stable for decades and even centuries. However, honey is susceptible to physical and chemical changes during storage; it tends to darken and lose its aroma and flavor. This is a temperature-dependent process, making the shelf-life of honey difficult to define. For practical purposes, a shelf-life of two years is often stated. Properly processed, packaged and stored honey retains its quality for a long time.

The best storage temperature for bee honey

Processed honey should be stored between 64-75°F (18- 24°C). Honey can be exposed to higher temperatures for brief periods; however, heat damage is cumulative so heat exposure should be limited. It is best to minimize temperature fluctuations and avoid storing honey near heat sources. The recommended storage temperature for unprocessed honey is below 50°F (10°C). The ideal temperature for both unprocessed and processed honey is below 32°F (0°C). Cooler temperatures best preserve the aroma, flavor and color of unprocessed honey.

Crystallized bee honey

Most honeys are supersaturated with respect to glucose which may cause glucose to crystallize spontaneously at room temperature in the form of glucose mono hydrate.  The rate at which crystallization occurs depends on the origin of the honey and the methods by which it was processed and handled. Crystallization may be reversed by heating which “melts” the crystals.

It is also possible to induce and control crystallization to produce creamed honeys. This process yields very fine crystals and a smooth product with a peanut butter-like texture. Creamed honeys can be flavored or mixed with other ingredients such as nuts, fruits or dairy products.

Uncontrolled crystallization of honey is undesirable. Spontaneous crystallization causes the product to become cloudy and less appealing to the consumer. It results in separation into two phases: a liquid phase on top and a more solid phase at the bottom of the container. The higher moisture content and the fructose content of the liquid phase can allow naturally occurring osmophilic yeasts to multiply and ferment the honey. Pasteurized honey in sealed containers may crystallize but is generally not liable to ferment.

A honey with a glucose/water ratio < 1.7 tends to remain liquid for a long time, while one with a ratio > 2.1 usually crystallizes quickly. It has been observed that honeys with a high percentage of fructose remain liquid for a long time. Thus other ratios such as fructose/glucose and (glucose minus water)/fructose have been proposed. The use of these ratios to predict crystallization is possible only when comparing honeys which differ significantly in sugar composition.

Physio-chemical factors influence crystallization and fermentation

Crystallization of honey is most rapid at 52-59°F (11-15°C). Some preventative measures may be taken, including:
  • Storing at temperatures which delay crystallization (<52°F, 11°C)
  • Preventing absorption of atmospheric moisture by tightly closing containers during storage 
The fermentation process is essentially dependent on the initial count of microorganisms in the product, the storage time and temperature, and the moisture content of the honey. The most important cause of fermentation in honey is the increase in its free-water content.

Honey with moisture content below 17.1% does not ferment. The stability of honey with a moisture content > 17.1% depends on its microbial content.  Pasteurized honey (available commercially) generally does not ferment because the microbial content has been reduced. Honey is highly stable against microbial growth because of its low water activity, low moisture content, low pH, and antimicrobial constituents. 

What is done by processors to reduce the risk of unwanted crystallization?

During processing, several steps are taken to prolong the liquid state of honey. Pasteurization delays the process of crystallization by dissolving any crystals that may be present in the crude product. Pasteurization also affects yeast cells which considerably reduces the possibility of fermentation. Recommended pasteurization treatments include flash pasteurization (170 °F for a few seconds) or heating at 145°F for 30 minutes.

Filtering under pressure enhances the clear brilliant color of honey and removes some potential crystallization nuclei such as undissolved glucose crystals, air bubbles, pollen grains or any other large particles. The filling temperature of bottles and other honey containers has an impact on crystallization as well. Honey bottled at temperatures of 104°F (40°C) or higher (up to 130-140°F, 55-60°C) crystallizes significantly more slowly. 

Is the container in which honey is stored important?

Some researchers have demonstrated that honey stored in low density polyethylene containers can lose moisture over time. This loss of moisture could contribute to crystallization.

It is important to store honey in air-tight containers. This protects it from external moisture which the honey may absorb. Properly sanitized and sealed stainless steel drums in good condition are perfect for extended storage of large quantities of honey.

A high quality product is essential for every honey operation. Managing key factors in the extraction process will affect honey quality.

Excessive heat during extraction will darken the honey. Certain export markets have minimum standards for diastase (an enzyme which can be destroyed by heat) and the level of sugar breakdown due to heat. To prevent heat damage to honey, producers need to carefully manage the wax melting process and pay attention to storage conditions.

The process of extraction introduces air, bee parts and beeswax. These impurities cause the honey to granulate more readily. Management practices to reduce natural impurities focus on developing an extraction process that removes wax and bee parts, and reduces the amount of air incorporated into the honey.

Excessive moisture in honey may cause it to ferment. Furthermore, honey is hygroscope, meaning it will take on moisture from the surrounding air. Although very dry honey is not likely to ferment, it will become very hard when granulated. Pasteurizing will kill the natural yeasts in honey and thus prevent fermentation. However, pasteurization isn't a feasible practice for many beekeepers.

Crystallization is the process of granulating. Consumers have accepted finely granulated honey, but find a coarsely granulated product to be unsatisfactory. Crystallization is generally managed through proper storage temperatures.

References 

  1. White, J.W. Jr. 1978. Honey. In "Advances in Food Research," ed. C.O. Chichester, E.M. Mrak & G.F. Stewart. 24:288-374. Academic Press, New York.
  2. Doner, L.W. 1977. The Sugars of Honey - A Review. Journal of the Science of Food and Agriculture 28:443.
  3. Crane, E. 1975. “Honey: A Comprehensive Survey.” Heinemann, London.
  4. Jiménez, M. et al. 1994. Influence of the Storage Conditions on Some Physicochemical and Mycological Parameters of Honey. Journal of the Science of Food and Agriculture 64(1):67-74.
  5. White, J.W. Jr. 1975. Physical Characteristics of Honey. In: “Honey: A Comprehensive Survey.” ed. Crane E., pp. 157-206. Heinemann, London.
  6. Sanz, S. et al. 1995. Fermentation Problem in Spanish North-Coast Honey. Journal of Food Protection 58(5):515.
  7. Assil, H.I. et al. 1991. Crystal Control in Processed Liquid Honey. Journal of Food Science 56(4):1034.


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