storage. Lipase a c t ~ i s~respomible ~ t ~ for increased rancidity e butter. Butter i d e c t e d with mold so sli is not visibly apparent at the time of stoa age will sometime5 exhibit considerable mold when removed. Eggs in the shell ing temperature, became if frozen, ill coagulate. Storage eggs are subject to the same 0 a lesser deger: than those stored a t a higher The changes a:e loss d ni~istuie,increase in bes of the fat,, increase in an-nmonia in the yolks, changing, but in many respects history is un~ ~ ~ ~repeating ~ n aitself. ~ e Feuhgton’s ~ y statements of 1908 may again be the rule and not the exception. 8%present the rendering weliie of bad meat is c ~ n s ~ ~ e Lit ~ ~eratrmre , ~ ~ yei t ed less theen its value as l a w material. for the ~ a n u ~ aof~mu~ ~ r e(1) Rouse of Representatives, 66th Corrgu., 1 s t Session, Cold Storage Legislation, Hearing before comrn, on b g r . , 1 9 1 9 ~ e. The Massachusetts inspecto (2) Ibid., p p ~46, 47, 49, 51. more bad beef and
than durmg many pP fillding and confiscating muoh had in one instance they made a co&eation in a saueage %&my operating under federal inspection. The odd storage groeess k not sespgnfiiblefor these COX&tiom, and it is hardly to be expected that warehouse employees will investigate the conditfion of each barrel of meat 888
(3) Ibid., p,387. (4) Lythgoe, H. C., Atti. C Q ~ ~ infern. P . ehim., X CongT,, 4, 610--18 (1938). ( 5 ) Lytligoe, H. C., Ice and Refriiiye~at(on,91, No, 4 (1926). (6) Psnnicyton, M. E., U. 8 . Dept. Agr., Bur. Chsrn. Ruli. 115 (1908). (7) Rept. of Cornm. t o Inveetigate Subject of Cold Storage of Food,
Maes. Houas Do,um,?a% 1133 (1912). (8) Bbid., gg. 67-8. ( 9 ) 5paskea, Royden, SIZt, E3sning R&, Silly I N , 1942.
January, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
39
Courtesy, Parker Ruatproof Company
Feeder End of Installation Built b y Wean Engineering Company f o r Bonderizing Black Plate
and steel. Now interest attaches to the steel problem, and consideration is being given to the alternate or required use of glass in place of metal containers. The basis for the container changea which have been ordered is not to be found in the discussions of the OPM days. The background lies in the work which was done much earlier in the laboratories of the can manufacturers. It is questionable whether anyone can say definitely just when work on substitute containers began, but some work on black iron containers was underway in the early twenties. Also, the Quartermaster Corps had an interest in some experimental packs in black iron cans which were being studied by this laboratory, and the interest was not in tin conservation but in the avoidance of glare which might result from the reflection of sunlight from bright tin plate. One of the first conferences, if not the first, to consider ways and means of conserving tin and of arriving a t an effective reduction in its use for metal containers was called by the chief of the conservation unit of the Office of Production Management in April, 1941. The principal subjects for discussion were: 1. Nonessential civilian uses of tin can containers, curtailment of which might be effected with minimum hardship in the event of a shortage of tin. 2. Possibility of developing substitutes that could be used for such purposes. 3. Possible effect of reducing t o various percentages the amount of tin coating on containers.
The conference amounted chiefly to an exploration of the means of effecting reduction in tin consumption; but no definite proposals were made, and the meeting adjourned on the note that the can manufacturing industry would make reasonable changes where practicable and would hold itself in readiness to make still further changes if necessary. The net result was a prompt reduction of 10 per cent tin coating (from 1.50 to 1.35 pounds per base box pot yield) for cans to be used for packing a majority of processed canned products, but excluding certain so-called class 1 products (kraut, pigmented fruits, and other products of corrosive character),
Further savings were effected by the reduction or complete prohibition of the use of tin for containers used in packaging nonprocessed foods. These reductions were progressive until Order M-81 became operative nine or ten months later. Then a limit of 1.25 pounds per base box was set for containers for most of the processed products that were allowed to be packed. This amounted to a reduction of about 17 per cent from the original weight.
Reduction in tin content The requirement in M-81 had to have some experimental basis, and its genesis was in a so-called tin-conservation pack which was put up in the fall of 1940 to test the effect of the extreme reduction in tin coating of from 1.50 to 1.25 pounds. In the main, this represented a coordination of the work already underway in the laboratories of can manufacturers and was a collaborative venture. The can manufacturers supplied the containers and most of the products, and the National Canners Association conducted the tests. Colonel Paul P. Logan, Quartermaster Corps, who was one of the first to see the need of tin conservation, played a leading part in planning the program. The test cans and control cans were packed with various food products selected to represent major classes with refer-, ence to their action on tin plate. Twelve typical food products were canned, representing fruits, vegetables, fish, milk, and army rations. Among these products were foods which would be expected to produce varying degrees of corrosion, perforation, hydrogen springer formation, and iron and tin discoloration. Packs were incubated a t 85" F., B storage temperature which would reasonably accelerate any abnormalities that might occur by reason of the lighter tin coating without producing such false effects as might result a t a substantially higher temperature. Periodic cuttings and examinations were made over an 18-month period, the examinations including organoleptic observations, visual examination of the cans for evidence of corrosion or discoloration, and chemical tests of the contents for tin and iron.
40
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1943
solder with the original composition 97.5 per cent lead-2.5 per cent silver is being used commercially for containers made of hot-dipped plate and electrolytic plate, but not Bonderized plate. Unsatisfactory experience with the last is due to the fact that the solder does not alloy readily with the steel. Experience showed further that, when the lead-silver solder is used, tin is picked up from the cans and the composition of the solder bath reaches an equilibrium a t approximately 2 per cent silver-5.5 per cent tin-92.5 per cent lead. The question has been raised as to whether, when the highlead solder is used, we may expect a greater lead pickup in the food than would be expected with the 40 per cent tin-60 per cent lead alloy. In the conventional “sanitary” type of can little, if any, solder is exposed to the can contents except on rare occasions when the solder is excessively sweated through the seams. I n the case of the floated-end type of can a small area of solder is always in contact with the can contents. Commercial experience over many years and experimental evidence have shown that the lead pickup from the 40-60 solder is so small as t o cause no concern. The relative degrees of lead pickup from the 40-60 solder, the lead-silver solder, and lead-silver solder with two levels of tin (2.5 and 5 per cent) are being studied here. The method is empirical and constitutes an exaggerated test in that a relatively large area of solder coated on a tin disk is brought into contact with the test food in a deleaded glas8 jar which is subsequently sealed, processed, and held in storage at 98’ F. The test foods are evaporated milk, orange juice, chopped green beans, and corned beef hamburger. Early results indicate that on the basis of maximum expected exposure the difference in lead pickup is not significant. Supplementing the study of the solubility of lead from solder in different foods, an elaborate series of feeding tests
% Strength of 40 Tin-60 Lead Solder Solder
100x
40 tin-60 lead
96%
35 t i n 4 5 lead
30 tin-70 lead
90 %
06 X
25 tin-75 lead
41
is being made a t Yale University, under George R. Cowgill’s direction; pellets of the lead-silver solder, alone and with two levels of tin, are being fed to rats in exaggerated amounts. This obviously is a public health investigation, and is a continuation of a study which has begn underway a t Yale for over two years on the effect of ingestion of metallic solder of 40 per cent tin-60 per cent lead composition. I n the first study both rats and dogs were used as test animals, and lead pickup by the animals was essentially negative.
Glass containers Glass containers have been referred to frequently as substitute containers. This follows a fairly general misconception that only foods which are processed in metal containers are “canned” foods. That is not the case at all, and glass containers have been established in their own right in modern canning. Glass, then, provides the material for alternate, rather than substitute, containers for heat-processed foods. In 1941 fruits and vegetables packed in glass amounted to 14,000,000 cases, or about 4 per cent of the total. For 1942 it is estimated that the glass pack will reach 31,000,000 cases, or 11 per cent of the total. I n this connection, however, it must be emphasized that under Conservation Order M-119, issued in the interest of rubber conservation, there cannot be any substantial turning to the use of glass for products for which tin is prohibited under Order M-81. As a practical matter the situation seems to have resolved itself into determining, first, what foods should be permitted as heat-processed products in either metal or glass containers and, secondly, what the proper balance is between the two, considering the necessity for conserving both tin and rubber. From the standpoint of canning technology a change-over from one type of container to another calls for material changes in operation. Not only is an equipment problem involved, but the usual procedures must be adjusted to meet the change. In particular, exhausting, processing, and cooling methods must be revised and additional equipment provided. Through editorial columns and elsewhere, much has been said about the possibility of plastic, fiber, or other nonmetal or nonglass containers as substitutes for the conventional containers; but nothing has yet come to light which suggests the utility of such substitutes for heat-processed foods. This is not to say that the eyes of canning technologists are cloged to such a possibility, but those who have had experience in testing even minor changes in containers know that should a plastic or fiber container be produced which theoretically and experimentally appears to fulfill all the requirements of an efficient container, much time-consuming work will be necessary to get the “bugs” out of it. However, should a promising substitute come to view, the best technological talent in the industry will give major attention to its proper testing.
Canning methods 20 tin-80 lead
2.5 silver-97.5 lead (eutectic solder mixt. before t i n pickup occurs)
127 %
2.25 silver-5 tin-92.751ead (compn. aotually experienced when manufacturing cans where tin pickup hag stsbiliaed in solder bath)
lo8 x
I
-
Relative Eon ding Stren gfhs of Reduced Tin Con ten t Solders a t 250°F. Courteny, American Can Company
Everyone who has given thought to the subject recognizes the effect on canning practice of the rapidly changing container situation. However, few have realized the extent to which the various Conservation Orders have influenced canning methods. This has been especially true in regard to formulation of products, but not entirely so. The motivation of such restrictions and requirements has been to make optimum use of the container materials which are available. Without attempting to cover this point exhaustively, I wish to cite a few examples. Under the original Order M-81, dried products were excluded, not only aa mch but in combination with the canning of fresh vegetables. Potatoes were excluded. Thus, there was prohibition against the packing of mixed vegetables using
42
3AC A N D E N Q I N E E
potatoes or dried products such as lima beam or peas. It is my understanding that no proceased vegetables may be used in any mixture of vegetables and, for purposes of definition, frozen vegetables are held to be proceased. This would prohibit also the canning of the mixture of such a popular product as carrots and peas if either ingredient had been either cann,ed or frozen. It has even been suggested that the cold storage of vegetab1.e~ constitutes processing, ~tlllhough it w ~ u l d appear that this extension of the defiizition would be dificult t o justify. It is well known that ready-to-servc soups have, by order, been displaced by condensed soups. The background of this change is Order 31-81, and t h e aaneridrnent, issued irr April, sets forth what kinds of soups may be pecked and specifies the lower limit of dry solids which would apply to ea,ch kind. M-81-a, as amended in June, went further a,nd stipixlated minimum solids, or gravity, for certain tomato products, notably in the case of pulp or pur&, the specification for wvhich was lifted from 8.7 per cent) salt-free solids (as provided in the standard of identity) to 10.7 per cent, Other examples could be cited and all of them t o a greater or lesser degree influence plant practice. A nohble example of voluntary action on the part of one branch of the industry to coordinate its policy with the conservation program occurred when the shrimp canners, RS an industry, suggested it be made nmndatory khat the drained weight of canned shrimp in the can be increased substantia6ly. This desk, was made legally effective after the usual hearing by an order issued by the Federal Security Agency, which fixed the weights at certain minimums according to size of can and style of pack.
Val. 39, No. B
Another peacehime deve1opmcu.t which. under other oireumatanoas would receive Ear more attention t,han i s given here, i s the increasing application on 8, coxrimercial scale of the principle of high texnperatu~e~short t i m sterilkitiora, or pasteuri~ation, of canned fruit and vegeti~blejuices. The principle i s aimoet mkiversa!iy empiogd in %he canning 01 citrus juices and has conic: inlo \vide use with the vegetabic juices. ‘6he developnxnt follows the direct or irnpiicti prophecy mads by Balk ( 2 ) before the 1837 Food Techoiogy Conference at M. 1, 9.‘. k t the same conforeme hyers ( 1 ) discussed flash pasteurimlion i>E fruit juices, The: principk aa applied t o uanr;ed vegetables is jimt mund a8 if; is in t l ~ e case of acid products, but very high ten1perntures are necessary for short-time ation of vege6nblcs, and the application calls for r experiment,al work reqiiiring specialized equipment, Coxisequently such work carmot bo mdertaken during the wm=. ieaary reaearn:h There i s milch activity ia 1;he field of nutrition, nnd practically all of it da,tes back t o the Resident’s Conference: or1 Nutrition in Mey, 1941. PreeCplt stsadles on the autrit,ion of canned foods in 8 sense &to to that the initial ttndwtaking. Fcx mom canning industry supportod work of Dnia9er~ity,as evic‘benaedby i h e many rcpnrta by SV. 13 Eddy eontent ni‘ onnmd prclducts, Il‘hi~wnrlr e!irPrijri:it,ed in been a groat accu.!rrulatiora v i t x n h s a.nd nrethodcl tbc ir:tlu.s”,ry i s nwalse letlgc 01).the prot,cztiive
factors. For the better part of 1942, iri scientific Iricetinga the referenceB to changes in focjd production and bandling, and in fact to other technieal mattors, have been associated largely with the war situation. This carriea the suggestion that almost everything in the nature of development just prior to the outbreak of hostilities mas in anticipation of the ,merr raost work stopped except gency, and that whexi ~ a came that which w&s directly tied to the prosecution of the war‘. Perhaps that i s the way it should be, but there lias been every reason to carry on to a reamiable conclusion some of the inore promising lines of work which wcre well under way when war was considered by many of us to be fairly remote possibility. One of the aece7it advances in canning I.echno?ogy not associated with the war has becn the definition of practicable methods to stabilize to u, high degree the cbllorophylR of green vegetables such as peas. One method has recently been the subject of a hearing before the Food aird Drug Administration on a petition t o amend the gtaildktrd of identity for canned peas t o include peas 57hicl-1had been subjected to the stabilization treatment. The hearing covered a, period of several days, during which there was a thorough exploration, under quasi court procedure, of all the important technological details and many minor ones. To state the matter briefly, the stabilization of the green color by the method is the rceult of the adjustment and CQiltrOl of pII by treatment with small quantities of harmless alkaline reagents. This control results in the maintenance of green color by preventing, substantially, the dissociation of magnesium from the chlnrophyll molecule. Peas 60 treated have been canned to a commercial extent. The method of stabilization lacks perfection and work toward that end remains t o be done. Further investigation of the problem must wait until we can give renewed attention to peacetime matter^, but B noteworthy advance has been achieved.
taken during the em:n’so of collaborative studies will be or will be placed with hi!: x l i This part of elle l\mk is d’
ca,tions or’ tbia line af !.e,udy
81’0 &lnle;attXrrr
with engineering in reaching the objectj veri, But before emon w ~ c htcchnologieal ’Investigation, wc; must hwve forms;i;ion which ’ive are noiv attc~nytirrgLO obt:liil. I,iBar“at*rra:a:ibs:ci
Ganu”, 1942. (4) Rohnnan, E. F., NatS. Canners Aci-oc,, PluEI. 19-%(1937). ( 6 ) Lappert, T. W,, I ? n n -Age. 149, 29 (April 30, 1042). (6) Lueok, R. XI., Pro& Inst. Food Tech., I942 728 (1942)
