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processed cheese frequently becomes discolored on the surface during storage, a defect which has been traced to the foil used in wrapping the loaves.
FROZEN CREAM One other dairy product which offers a number of problems in preservation is frozen cream. The separation of cream of 40 to 50 per cent butter fat, followed by pasteurization and freezing, is becoming increasingly important as a means of carrying surplus butter fat over from the early summer to the midwinter season. This frozen cream is used mainly in the preparation of ice cream mixes in which homogenization is employed for re-dispersion of the butter fat. Rancidity, tallowiness, fishiness, and metallic and storage flavors are frequently encountered in frozen cream. These arise from the same chemical and bacteriological changes which have been described as characteristic of other dairy products. Just recently the quick-freezing of cream has received attention because of the present prominence of the general subject of quick-freezing, although so far as known no such product is yet available on the market. Another recent development is the production of a cream containing 80 per cent butter fat, whose storage should present no greater difficulty than does that of butter.
I ST R Y
Vol. 24, No. 6
CONCLUSION It is hoped that sufficient emphasis has been given to the points cited to indicate that a wide field remains for the work of the chemist and bacteriologist Improvements in the condition of dairy products after long storage will go far toward leveling off the seasonal price changes which are characteristic of the industry, and may prove of large economic value in permitting longer storage of surpluses during seasons of low prices, such as have been experienced during the past year. LITERATURE CITED (1) Bur. Markets, Bull. 729, U. S. Dept. of Agriculture (1918). (2) Food Industries, 4, 2 (1932). (3) Hammer, B. W., and Cordes, W. A . , Iowa Agr. Expt. Sta., Bzcil. 68 (1918). (4) Hess, A. F., Lewis, J. M., MacLeod, F. L., and Thomas, B. H., J. Am. Med. Assoc., 96, 370 (1931). ( 5 ) Newlander, J. 8., and Euenberger, H. R., Vt. Agr. Expt. Sta., Bull. 299 (1920). (6) Rogers, L. A,, (Associates of) "Fundamentals of Dairy Science," Chap. XIV, Chemical Catalog, 1928. (7) Sommer, H. H., and Smit, B. J . , Wis. Agr. Expt. Sta., Research BUZZ. 57 (1923). RECEIVED April 7, 1932.
Factors in Commercial Cold Storage JAMESC. IRWIN,JR., United States Cold Storage Corporation, Chicago, Ill.
C
OLD storage, which occupies such a prominent position
in the field of food preservation, may be divided in two general classes in relation to operation and application of development. One is the cold storage operated by the packer in conjunction with his various operations, subject to a unified supervision which controls preparation, handling, storage, and distribution. For him cold storage is a process phase in his program of production and selling, and a regulator rather than a primary source of profit. The commercial cold storage warehouse, on the other hand, is dealing with numerous clients and handling products over which it has little or no control before they are received for storage. While the storage must maintain the material and return it in the best possible condition, its methods are still subject to the established ideas of the storer, who is in general slow to accept changes. The selling of cold storage service is highly competitive, and, in the establishment of fair rates, investment charges have a large effect so that the premium obtained from radical changes in construction or equipment frequently cannot be counted on to be reflected in earnings. I n addition, scheduling of commodities through storage introduces difficulties and limitations on control. Goods received either in car lots or in small lots for car-lot accumulation a t one period may be withdrawn a t any time either in car lots or a few packages a t a time from rooms containing, from necessity of economical operation, from twenty-five to fifty or more cars. In setting up ideal conditions for commercial cold storage, the weight of these factors must be taken into account. Cold storage facilities are of two distinct classes: cooler, covering temperatures above freezing point; and freezer, applying to temperatures below 25" F. In the cooler, no marked physical changes are produced except the delayed maturing of some fruits and vegetables, and the storage life is shorter. I n the freezer, the commodity, if no$ received frozen, is frozen or partly frozen as quickly as conditions
warrant and with sufficiently low temperature the storage life is practically unlimited. Much closer supervision is required during the storage period in the cooler, while for the freezer commodities, emphasis must be placed on processing before being received for storage, and on the freezing period. C O L D STOR.4GE
I N COOLERS
For the cooler, temperatures are pretty well established just a safe distance above the freezing point of the commodity.
I n some cases these are too low, and in other cases higher temperatures give equally good results; but, unless undesirable effects are produced, it is obviously the point which will result in the longest storage life. The tendency is toward somewhat lower temperatures than formerly. Celery, for example, is held a t 33" to 34" F. in many warehouses, but others have found that temperatures which may result in slight external breakdown or show a trace of frost in storage give, over long periods, a better marketable portion. Humidity in. the cooler ranks close to temperature in its effect on out-of-storage quality. I n general, it is advantageous to maintain the highest possible humidity without serious mold growth, but for certain commodities the humidity must be much lower to maintain texture, as in cereals or tobacco; or by those commodities which have a tendency to absorb moisture and which are damaged by moisture absorption, as candy and dried fruits. Humidity control in coolers is comparatively simple, as saturation is rarely required. Methods in satisfactory use range from recirculating air in contact with a brine of the desired vapor pressure through humidifying by vaporizing or atomizing or merely sprinkling the floors, and dehumidifying by passing the air in the room over calcium chloride. The determination of humidity is frequently the weak point in humidity control, as the sling psychrometer requires the greatest care and patience a t 32" F. or below. Other devices
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I K D U S T R I A L A N D E N G IN E E R I K G C H E M I S T R Y
have met with some success but are subject to errors which the operator must appreciate. As a check, direct measurement by absorption of water vapor with phosphorus pentoxide is employed, and a t freezer temperatures such a method must be used for reasonable accuracy. There is considerable interest a t present in other atmospheric modifications. Ozonation has become standard practice for some commodities, particularly eggs. It appears to reduce mold growth, and hence allows higher humidities and considerably reduces the possibility of off-flavors from cases and packages. Again, particularly with eggs and some fruits, interesting results have been obtained with abnormally high concentrations of carbon dioxide, and this fieldFppears to be very promising. While some sealed containers are being used on a commercial scale, it is believed that the greatest practical application will be found in protected rooms wtth atmospheres noninjurious to workmen. To meet this, it may not be possible to secure full effects, but it is probable that practical considerations noted above will outweigh the loss. This applies to other atmospheres which have been suggested or experimentally applied. In this connection more or less air-tight liners for egg cases have recently found some favor, but the effect of these in storage has not been wholly satisfactory. Progress has been made, but much more is to be desired, in regard to handling before storage. Proper grading and packing, as well as immediate cooling a t point of origin are vital factors in storage life. The first two are well established, and the last is accepted in certain sections as to fruits and vegetables; but, except in largest producing areas, methods of gathering and accumulating eggs leave much to be desired both as to time and temperature. Because of delays in accumulation of eggs, effects are set up over which the warehouseman has no control, and which are not apparent in the present routine examination a t the time the eggs are received. It is believed that more complete examination of egg contents should be practiced for the protection of both owner and warehouse, and it is desirable that criteria be established for the quality of egg contents. COLDSTORAGE I N FREEZERS In freezers there is a marked tendency toward lower temperature and, except for curing meat, it is seldom that temperatures above 10" F. are considered; most products are carried a t zero or below. While i t is believed that there is advantage in extremely low temperatures for some commodities, there is evidence that this cannot be accepted universally and that low temperatures may cause damage to some items which are excellently held a t high temperatures. I n addition, with lower temperatures there is a rise not only in the cost of construction and refrigeration requirements, but a very rapid rise in the cost per unit of refrigeration for which a corresponding increase in value must be shown. The dehydration of protein material under freezing has been given some attention and is worthy of much more study. It is believed that a better knowledge of this process will determine future practice both as to freezing and holding temperatures, and that it will result in a return to higher temperatures for some commodities. Other changes are favorably affected
VITAMINA FROM CAROTENE. Vitamin A is produced when ultraviolet light of a particular wave length acts on carotene, the yellow pigment found in carrots, yellow corn, butter, egg-yolk, etc., according t o F. P. Bowden and C. P. Snow, of Cambridge University, in a report t o the British scientific journal, Nature. Ultra-violet light of wave length 2650 A, transforms the mother substance, carotene, into vitamin A. This light is too
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by lower temperatures, probably without limit, and a t the present time the optimum point for most commodities is not definitely determined. Atmospheric conditioning in the freezer is almost wholly a question of humidity. Where oxidation has an effect it will probably be controlled in processing and by suitable packing. According to present knowledge saturation is universally desired for the freezer and during freezing. Although this might a t first seem a simple achievement, local variations in temperature and moisture capacity of packages introduce difficulties. The cooling medium must be a t a temperature lower than the commodity stored so that conditions favorable for moisture migration are always present. While glazing with ice is common in fish freezing, it has not been accepted in other lines and would require a rsdical revision in quality standards, selling practice, and packages. Ice will help to build up freezer humidity, and water evaporation is used to some extent. To obtain a humidity of 95 per cent in a certain room four times the amount of water required to saturate the volume of the room is evaporated by electric heaters each day. Under these conditions, shrinkage is reduced but far from eliminated. I n the matter of freezing, the industry is a t much variance. The bringing into prominence of quick-freezing a few years ago has resulted in a great amount of healthy discussion and research, along with the usual flood of overenthusiastic and baseless assertions. Rapidity of freezing is undoubtedly desirable. Whether this should be secured by extremely low temperatures is more questionable, as mentioned in regard to holding temperatures. I n the earliest stages of this activity it is probable that many of the desirable qualities attributed to quick-freezing were due to selection of material frozen and the processing to which it was subjected before freezing, rather than t o the freezing process itself. CONCLU6ION
The object and duty of the warehouseman is to supply service that will result in the highest quality in goods delivered from storage, but it is most essential that he receive a reasonable profit from his operations. Any increases in operating cost must be added to his storage rates if his business is to be on a sound basis. On the other hand, the storer who is dealing in commodities of comparatively low value must have a very real increase in the value of his commodity to warrant his paying these higher rates. This, of course, is general for any industry, but the narrow margin of profit of both the warehouseman and the storer requires particular attention with regard to commercial cold storage. Advances are being made and will continue. There is still much to be accomplished in determining most favorable operating conditions and securing their acceptance by the warehouseman and the storer. Cooperation among various agencies is necessary, and, in particular, close contact of this division of the d 4CHEMICAL ~ SOCIETY ~with the Associa~ ~ tion of Refrigerated Warehouses of the American Warehousemen's Association, and with the American Society of Refrigerating Engineers, is to be recommended. RECEIVED April 7 , 1932.
short to be seen by human eyes but it can be recorded on photographic plates. The production of vitamin A was checked, in that the substance formed absorbs ultra-violet light in the way that known vitamin A does. It also yields a colored substance when treated with antimony chloride-another test for vitamin A. The irradiated carotene has not yet been tested biologically upon animals, however.
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