TY  - JOUR
AB  - The body design of the lorry was then modified to be of the “cupboard” type, with the refrigerant in the storage chamber for the goods. A revolutionary step was taken by the introduction of solid carbon dioxide as refrigerant. This material is made by supercooling liquid carbon dioxide by its own evaporation until a “snow” is formed and then compressing this “snow” to a specific gravity of 1·5. The solid block so formed has a greater refrigerating effect per pound than ice, and a much lower temperature (=108° F.). It evaporates without passing through the liquid stage and on account of this property it has been called “Dry‐Ice” in America and “Dri‐Kold” in England. It is clean in use, but relatively expensive (about 2d. a lb.), and its low working temperature is a disadvantage, as it makes difficulties in controlling the temperature of the refrigerated space. Its use has eliminated all corrosion and enabled the insulation design and body building design to be simplified and made more efficient. The presence of carbon dioxide gas in the refrigerated space is often a disadvantage; when this occurs the solid carbon dioxide has to be held in a separate container and the heat from the refrigerated chamber led to it by conductor plates, or by a secondary refrigerant, or by a moving air stream. The high price of solid carbon dioxide and the difficulty of controlling the temperature with it have led many engineers to seek other solutions of the problem of refrigerating vehicles. The use of a small compressor outfit, which has its own motive power (either internal combustion engine or electric motor) or is driven from the axle of the vehicle, has been developed and has a following. The small size of these units causes inefficiency and uneconomical running, and the possibility of breakdown, with consequent loss of refrigerating power and spoiling of the load, is a nightmare to the operator. Most recently of all a return has been made to the eutectic tank method. This method suffered from the necessity of removing the tanks on the return of the empty vehicle and replacing them by a fresh set which had been freezing in a special equipment. This took time and two sets of tanks were needed besides the freezing equipment. Now the tanks are fixed in the vehicle; they have internal pipes which, when the vehicle is docked, are connected to a main refrigerating system, and flooded with liquid ammonia. This ammonia is evaporated by the compressor and freezes the eutectic solution which in turn refrigerates the vehicle when it is on the road. The system has the advantage of a stable, readily‐controlled temperature, absence of all mess, and the reliability and cheap running costs of a fixed large capacity refrigerating plant. The amount of eutectic used is such as to provide about 36 hours refrigeration on the road, so that no breakdown can result in the loss of the load. Mr. Milner Gray, in a section of his lecture in 1939 to the Royal Society of Arts on “The History and Development of Packaging” has already pointed out how social and economic changes in recent years have affected the distribution of foodstuffs. Smaller families and residences, and the increased pace of living have made popular the packaged food unit, which is easily purchased, handled and stored. The lecture dealt with the subject from the point of view of the designer of artistic packages, but the food manufacturer is obviously concerned with the effect of the package itself on the food it contains. It is a matter of commercial necessity for the large food factories of to‐day (with sales areas covering the whole of the United Kingdom) to ensure that their products shall reach all their customers in a satisfactory condition. The period which elapses between the goods leaving the factory and their reaching the customer varies, but the package must be such that the quality of the foodstuff is maintained for the desired period or “life” of the goods. A packaged foodstuff may be made or marred by its wrappings. Generally speaking, the main causes of spoiling in manufactured foodstuffs are mechanical damage, temperature effects, insect infestation, putrefaction, moisture‐exchange (dependent upon weather conditions), flavour contamination, and chemical changes such as development of rancidity and metallic contamination. The package can be constructed to give reasonable protection against all these factors, and a few illustrations will be given of how this is done. A package must necessarily be strong enough to prevent physical distortion of the product wrapped, but the question of functional designing of packages is not germane to the present lecture: the general principles of the strength of bulk containers was explained in lectures to the Royal Society of Arts by Mr. Chaplin and his colleagues from the Container Testing Laboratory at Princes Risborough. Prevention of insect infestation from outside sources is, of course, simply a matter of proper closure and choice of materials. Prevention of putrefaction, or spoiling by micro‐organisms is one of the chief purposes of a food wrapping, and bound up with the question of prevention of access to the food of putrefying organisms is that of prevention of infection of the food by organisms which might not themselves spoil it but which are harmful to human beings if eaten with the food. Medical Officers of Health have been concerned with the latter aspect for many years, and the present public demand for milk in individual containers, such as cartons or bottles, and for the large quantities of bread sold in sealed wrappers is no doubt due largely to their education of public opinion. Wrapped bread is usually sold in a sealed waxed paper packing, which, in addition to keeping the bread clean, also delays drying of crumb through moisture loss. The baker must, however, guard against the actual spoiling of his bread through wrapping. If the bread is packed too warm, mould growth in or on it may be promoted by the high moisture content of the atmosphere inside the waxed wrapper which is impermeable to moisture vapour. This impermeability has other effects, which will be considered later. Various proposals have been made to prevent mould growth on foods inside wrappers by impregnating the latter with compounds which volatilise slowly and inhibit the development of moulds and micro‐organisms. Compounds of the type of chloramine T (liberating chlorine in a damp atmosphere) have been patented for treating bread wrappers, while iodine, diphenyl and many other compounds have been proposed for treating wrappers to be placed round fruit. Some years ago a wrapper marketed to prevent meat spoiling was found to depend on the liberation of formaldehyde. Wrappers of these types cannot, however, be used on account of the danger of infringement of the Foods and Drugs Regulations if the foodstuff should absorb any of the volatile compound. The loss or gain of moisture by manufactured foodstuffs are two very important causes of food spoiling. Sponge cakes, under ordinary conditions of storage, soon become dry and unpalatable, while boiled sweets and toffee can be kept in good condition for a considerable time by the use of a suitably selected wrapper. Different types of wrappers allow the passage of moisture vapour at different rates, but for practical purposes they can be considered as either permeable or practically impermeable to moisture vapour. The rate of passage of moisture vapour through a wrapper has not necessarily any connection with the “airtightness.”
VL  - 43
IS  - 12
SN  - 0007-070X
DO  - 10.1108/eb011360
UR  - https://doi.org/10.1108/eb011360
PY  - 1941
Y1  - 1941/01/01
TI  - British Food Journal Volume 43 Issue 12 1941
T2  - British Food Journal
PB  - MCB UP Ltd
SP  - 111
EP  - 120
Y2  - 2024/04/23
ER  -