When we cut open bread rolls and hamburger buns that have been stored in the deep freeze for a period of time we observe a white ring just inside the

The phenomenon that you have observed is commonly referred to as ‘freezer burn’ and arises from the movement of water within and from the product while still in the deep freeze. It was reported by Pence et al. (1958) who examined the whitened areas of products exhibiting the phenomenon and observed that they had a greater number of tiny voids associed with starch granules. These voids were linked with ice cristls that had sublimated from whitin the starch granules, causing a greater opacity of th crumb and the whitened appearance. The change in the crumb texture fro, this effect also couses the crumb to have a harsh, dry eating quality arising from the lower moisture content. However, the effect does not come exclusively from the loss of moisture since the attempts to restore the crumb properties are unsuccessful enless substaintial ‘re-wetting’ of the crumb is applied.

Even thoung the product has been stored in a deep freeze running at about –20ºC not all of the aqueus phase in the product is ‘frozen’. This aries because of freeze-concentration effects and presence of consentration of the remaining aqueous phase increades and its ‘freezing point’ becomes lower (Cauvain and Young, 2000). Eventually the consentration may become so low that the solution will not freeze even at –20ºC.

Any increase in the product temperature during storage will enable some of the ‘unfrozen’ water present to diffuse from the product into the surrounding atmosphere. This clearly happens with may frozen products since it is not product is held in the storage freezer then the greater is the accumulation of snow as the product progressively dehydrates.

After the product has warmed in the storage freezer any subsequent refreezing will take place very slowly from the surface inwards. This creates an interesting effect because the center of the surface begins to freeze quite quickly, while a few millimeters under the surface freezes slowly. The end resuld is the formation of the while areas of freezer burn which commonly reflect the outer shape of the product.

The problem can be ninimised by paying attention to a few simple ‘housekeeping’ rules:

• Do not store the product for very long periods of time.

• Check the actual storage temperature over a period of running time. The set temperature in the deep freeze is nominal and the thermostat will allow some degree of fluctuation around the set point.

• Ensure that your storage freezer is regularly serviced and have the conditions of any automatic defrost cycles checked.

• As much as possible avoid actions that allow the freezer temperature to rise excessively. For example, keep doors closed as much as possible and minimize loading and unloading times as much as possible.