Bread is made by baking dough and crisps. White bread with white flour. Black bread is made with rye flour and corn, sometimes with some vitamins.
The equilibrium humidity of the heart of the bread is about 90%, so it is easy to lose moisture and become hard. The balanced moisture of the crust is relatively low, and it easily absorbs moisture and becomes wet in moist conditions. Therefore, the bread wrapping material should have moderate moisture resistance. If the water vapour permeability of the packaging material is too low, mold growth will be promoted and the crust will be soft. Conversely, if the moisture permeability of the packaging material is too high, the bread can easily dry and deteriorate. In addition, the cost of the bread wrapping material is low.
The bread begins to change after 4 to 7 days. The speed and degree of aging are related to the nature of the flour, the baking method and the storage conditions. Moisture transfers from starch to the internal protein part, and the starch changes, losing its tissue properties. Since the ageing of bread is directly related to its internal moisture content, the wrapping of bread must effectively prevent the loss of moisture.
The ideal packaging material should meet the following requirements: 1 Appearance is attractive; 2 can maintain proper shelf life; 3 adapt to automatic packaging machine operation; 4 has sufficient strength; 5 low cost; 6 has suitable moisture resistance; 7 Protect the bread from deformation.
Bread is usually wrapped in flexible packaging material. The main packaging materials are as follows:
(1) Wax paper From about the end of World War I, the bag was wrapped in wax paper, and it was wrapped in an automatic wrapping machine and sealed around it. Wax paper is the most economical packaging material. It also has sufficient stiffness on the automatic wrapping machine, sealing is easy, and it effectively prevents the bread from losing moisture. The disadvantage is that the transparency is not good, and the pain is easy to cause breathability, resulting in bread water dispersion and loss. Hair dry.
(2)Cellophane Before and after 1902, cellophane was used as a wrapping material for bread. In the early stages of application, attention was drawn to issues such as mechanical operational limitations, high costs, and non-heat sealable issues. Later, plastic glass cellophane appeared to solve the problem of semi-moisture resistance and heat sealing. By 1930, in 1955, the package was basically wrapped in cellophane. However, the packaging cost of cellophane is much higher than that of wax paper, and it is more suitable for packaging of high-grade bread. Domestic bread is currently mainly wrapped in wax paper.
(3) Plastic film In the country, polyethylene films were used to package bread around 1958. The packaging cost of polyethylene film is about 30% lower than that of cellophane. However, the thickness is thinner than the film and the machine operation process performance is poor. Soon, polypropylene film appeared, its transparency is better than polyethylene, and the stiffness is larger, and the machine operation performance is better. However, a pure polypropylene film has been brittle at a temperature of 17.7°C, and heat sealing is difficult. By 1962, polyethylene-polypropylene-polyethylene three-layer coextruded materials appeared, further satisfying the need for surface wrapping packages.
At present, about 90% of the bags are packaged in polyethylene plastic bags. Its advantages are that it can be used repeatedly, it is easy to take, the shelf life of bread is long, and it does not need to be bundled. It can be sealed by heat sealing or plastic coated metal wire, or it can be wrapped in polypropylene plastic bag. Mouth packed bread. More particular is the use of aluminum foil/composite or polyethylene composites or aluminum foil/polyethylene composites. Although this kind of packaging material is not transparent, it can protect vitamin B1 in bread from loss.
In addition, bread packaging uses shrink film and blister packaging. The polyoxyethylene shrink film for shrink packaging shrinks the bread. Blister packs are expensive but attractive.
Source: Food Industry Forum