PURPOSE OF THE LITERATURE REVIEW 



Freezing as a method of home food preservation 

 lias expanded rapidly during postwar years. Users 

 of home freezers and freezer locker plants require 

 sound information on methods for preparing, pack- 

 aging, freezing, and storing a wide variety of 

 foods and food products. Wliile much information 

 is available in the rapidly growing literature on 

 frozen foods, recommendations reaching users of 

 home freezers are often contradictory or lack 

 adequate research basis. This is especially true 

 in the area of frozen prepared and precooked foods, 

 where insistent demand for information that is 

 not available or complete emphasizes the need for 

 continued research. For tliese reasons, the Bureau 

 of Human Nutrition and Home Economics felt that a 

 critical review of methods recommended for the 

 preservation of foods by freezing and storage in 

 home freezers and freezer locker plants would be 

 of value in promoting uniformity in recommended 

 procedures and directing further research into 



those areas where available information is incom- 

 plete or conflicting. 



To make a critical evaluation of recommended 

 procedures, the Bureau sponsored a Conference on 

 Home FYeezing, which was lield March 14-17, 1949, 

 in Washington, U. C., and attended by food-freez- 

 ing specialists from institutions in various sec- 

 tions of the country. In preparation for this 

 conference, several members of the Bureau staff 

 collaborated in reviewing recent literature on 

 food freezing. From the assembled information 

 the following classified notes were developed to 

 guide the conterence discussions and serve as a 

 working tool for use by conferees. Rapid exhaustion 

 of the limited initial supply of mimeographed 

 copies and continued demand for the notes indicated 

 tliat a printed publication would be of value to 

 those engaged both in research and in the dissemi- 

 nation of information on home-freezing methods. 



THE CLASSIFIED NOTES 



file classified notes based on the literature 

 review are arranged in I'our main sections. In 

 the first section on vegetables and the second 

 section on fruit, information is tabulated on: 

 Tlie preparation of the food, chemical treatment, 

 heat treatment, cooling and type of pack recommended 

 for freezing. In the third and fourth sections on 

 prepared foods, information is tabulated on: 

 Formula, preparation, packaging, freezing temper- 

 ature, storage, thawing and heating for serving. 



Within each section the procedures which the 

 authors considered most applicable to home freezing 

 are set apart in one column. Other procedures 

 noted in the litera ture review are given in a sep- 

 arate column. 



Tlie authors wish to emphasize that the notes 

 are not presented as a complete review of food- 

 freezing literature. Publications reviewed were 

 largely limited to those giving directions based 

 on laboratory research or reporting concrete ex- 

 perimental data, and appearing within tlie last 10 

 years. To the extent that recent literature is 

 covered, tlie presentation of the review in the 

 classified notes, pages 3 - 95, serves certain 

 functions not served by an annotated bibliography 

 or the narrative review. Tlie grouping of proce- 

 dures from various sources provides for ready 

 comparison of recommendations that have been made 

 by different workers I'or the preparation ol' foods 

 for freezing. It also emphasizes the incompleteness 

 or conflict of information — which in turn indicates 

 the need for further research. 



SELECTION OF PROCEDURES 



The selection of procedures considered most 

 applicable to home freezing was based not only on 

 preponderance of opinion as expressed in available 

 publications, but also on unpublished data in Bureau 

 files, the authors' research experience, their 



evaluation of available information, and careful 

 consideration of practical household usage. 



In the category of preparation, lye peeling, 

 wliich provides a rapid and economical method for 

 peeling some fruits and vegetables, was not con- 

 sidered as a practical metliod for household use 

 because of the difficulties involved in proper 

 control of the process, and potential dangers in- 

 volved in its use. 



Among the chemical treatments, the use of cal- 

 cium salts for the firming of some products, par- 

 ticularly frozen apples, which is being used 

 successfully in commercial practice, was also 

 considered to be a procedure that would be gen- 

 erally impractical for household use. Its success- 

 tUl application normally requires preliminary ex- 

 perimental testing to determine tlie concentrations 

 and treatments required for particular varieties 

 and stages of maturity, as well as more careful 

 control than the average household worker is pre- 

 pared to exercise. 



Wliile there is considerable variation in rec- 

 ommended procedures found in the literature, the 

 authors believe that those listed as most appli- 

 cable to home freezing of fruits and vegetables 

 are generally suitable for the production of sat- 

 isfactory frozen products. Information on the 

 preparation and freezing of prepared and precooked 

 foods is more limited and conflicting. In many 

 instances there is reason to believe that the 

 methods selected as most applicable do not result 

 in products that are entirely satisfactory. 



Preheating 



Steam versus boiling water. - -Directions are 

 given in tlie notes for preheating both in steam 

 and in boiling water. Preheating in boiling water 



