TEXAS AGRICULTURAL EXPERIMENT STATION A. B. CONNER, DIRECTOR College Station. Texas BULLETIN NO. 635 JULY 1943 DEVELOPMENT OF METHODS FOR SAFE PROCESSING OF HOME CANNED MEATS SYLVIA COVER, B. D‘. TURK, AND A. H. KERNS Division of Rural Home Rasearch AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS T. O. WALTON, President I luvs \I al-y-FFPP. ; \ 1 AE§IBUITUTE§&.55€G??EEE?GE§fifiiififiafii"faaag B 39—743— 41M—L18O Since farm people are being urged to increase their supply of home . produced meat, it is imperative that a canning procedure be recommended which not only is adequate to prevent danger from harmful bacteria but also is as economical of time as is consistent with safety. \Vhen spores * of Clostridium botulinum develop in food they produce a. toxin so potent that a minute amount if eaten is sufficient to cause death. While this a seldom happens in canned meat, contamination with these spores frOm the soil may occur when animals are slaughtered even under the best of conditions found on Texas farms and ranches. This study was made to find the lowest processing periods which would destroy Olo-stridium botulinum in canned meat and make it a safe food. The procedure recommended is as follows; First: Pack cold meat into containers, leave unsealed and heat for a specified time in a cooker from which steam js escap- ing. The time at which steam starts to flow from the cooker in a steady stream marks the beginning of “Steam- ing time.” “Steaming time” Varies in length according to the size of container as follows: N0. 1 cans 30 minutes No. 2 cans 60 minutes No. 3 cans 90 minutes Pint jars 60 minutes Quart jars 80 minutes Next: Immediately after “steaming time” is ellded, seal the 00n- tainers, return them quickly to the hot cooker, and begin processing at once. Process at 15 pounds according to size of container for the following periods of time: * No. 1 cans 50 minutes No. 2 cans 60‘ minutes No. 3 cans 85 minutes Pint jars 60 minutes Quart jars 75 minutes Finally: As soon after processing as the pressure on the gauge re- turns to zero, remove tin cans and cool quickly and thor- oughly in cold water. Leave the glass jars in the open ‘cooker until the liquid inside stops bubbling, then remove them and allow to cool in air at room temperature. ‘Introduction CONTENTS Plan of Work Heating Before Sealing Heat Penetration Tests Results From Heat Penetration Tests Inoculation Tests Results From Inoculation Tests Discuss-ion Acknowledgment Summary and Recommendations DEVELOPMENT OF METHODS FOR SAFE PROCESSIN i OF HOME CANNED MEAT . Sylvia Cover, Foods Specialist, R. D. Turk, Veterinarian, and A. H. Kerns, Electrical Engineer ‘During the war emergency, farm people» are being urged, to increase ir preservation of home produced foods as much as possible in order relieve the strain on processing and transportation facilities and yet g adequately fed. This report of safe processing periods is as timely if it had been planned for war use. When the Work was" begun, tin = only were used since they may be cooled much more quickly than s jars, but when the shortage of tin developed, the plans were changed include pint and quart glass jars. _ 5: < _7When meat is canned at home on Texas farms and ranches, a whole j ycass is frequently canned in one day. Under these circumstances, it F ofomes especially important (to use the shortest processing time con- tent with safety. QThe Bureau 0-f Home Economics, in 1936 and in 1943 (9) recom- nded that ground beef be processed at 15 pounds pressure for 90 _utes in N0. 2 cans" and pint jars and 120 minutes in quart jars. _s homemakers had found that meat would “keep” perfectly with uch shorter processes. The Texas Extension Service in 1940 (7) rec- mended 50 minutes for No. 1 cans, 65 minutes for No. 2 cans, 80 _nutes for No. 3 cans, 75 minutes for pint, and 90 minutes for quart . In certain parts of Texas, however, objections to the meat canning gram “were encountered among a few physicians because of the fear Jiotulinus poisoning if inadequate processing periods were used. Clostridium botulinum is widely distributed in nature. Meyer and , inbovsky (6) found this organism in virgin soil, in cultivated garden ' d field soils and their products, and on vegetables and fruits bought various cities and towns in California where this study was made. e organism is a strict anaerobe, growing‘ only in the absence of air “n11 at temperatures from 2000 (68°F) to 37.500 (99.5°F) on most ‘dinary media. According to Kelser (5) it is quite fastidious in its edia reaction requirements, a neutral or alkaline medium being neces- ry for best luxuriant growth. It will not grow in highly acid media. eat resistance of the spores" is far from uniform. Esty and Meyer (3) ' nd that the spores of Clostridium botulinum in juicesof 17 varieties if canned food resisted heating at 100°C (-212°F) for periods varying eirom less than 10 minutes to 230 minutes and that at 105°C (221°F, , pounds pressure) the he-at resistance varied from 3 to 80 minutes for '09 strains of Clostridium botulinum. Thus there is always a chance a 5!: Acidification greatly lowers the thermal death point, the spores being ’ filial: meat may become contaminated with a highly resistant strain. 6 _ BULLETIN NO. 635, TEXAS AGRICULTURAL EXPERIMENT STATION ~. most heat resistant in media of neutral reaction. Young moist‘ spores are the most resistant. When animals are killed at home, even under the most favorable conditions, such as under a tree in the yard or pasture, there is a pos- sibility of meat becoming contaminated with soil containing botulinus spores. Under less favorable conditions the possibility of such contam- ination is increased. Experimental work was needed to find the lowest processing periods" which would kill these spores and thereby make the meat safe from the toxin produced by this organism. Nelson and Knowles of North Dakota (8) used a sealing temperature of 86°F (30°C) but Texas people have been taught for years by their Extension Service workers to use a high sealing temperature followed by immediate processing. Using such directions, shorter processing peri- ods are required. Thus any recommendation of processing periods must set up the conditions used in heating before sealing. Plan of Work Since the destruction by heat of the spores of Clostridium botulinum depends on the temperatures reached and the lengths of time they are maintained it becomes important to determine What temperatures are reached and for how long they are maintained. Heat penetration studies supplied this information. The heat penetration data were used for calculating processing times using a complicated mathematical formula which had previously been tested extensively in commercial canning plants. Actual destruction of live spores was used as the final proof of safe processing. In all of these tests the temperature of the meat in the cans atseal- ing time was as high as 180°F. This is an important point‘ because lower sealing temperatures increase the time needed for processing. Several methods of obtaining this high sealing temperature were tested. Heatilng Before Sealing Heating before sealing drives air out of the container and reduces the chance of breaking the jars or of bulging the seams in tin cans during the processing under pressure. The higher the sealing temperature the shorter will be the time under pressure needed for the meat ‘to reach a temperature high enough to make it safe. Various methods have been recommended for obtaining a high tem- perature in the can before sealing: 1. boiling in a kettle and packing hot, 2. Cooking in an oven or in deep fat and packing hot, 3. packing cold and heating under pressure, and 4. packing cold and heating in flowing steam. The first three methods were found to have the follow- ing objections: When meat is boiled in a kettle or cooked in an oven or in deep fat before packing, it is somewhat difficult to pack and if the packing process is delayed to obtain a full even pack, the tem- METHODS? FOR SAFE PROCESSING OF HO'ME CANNED MEATS 7 Qperature of the meat when sealed may be lower than 180°F. When cold meat is packed into containers and heated under pressure (7), the -.temperature of the meat inside is‘ frequently raised above the boiling fpoint of water. After the fire is turned out the meat temperature may above that of the cooker for several minutes even after the pressure iigauge has returned to zero (Fig. 1). If the petcock is opened and the l n u I I ? Cooker Cooker Cooker .- , u ___ ‘f-su‘... ___ 240,; ‘o.’ nonfat,’ -_ 24D _._ ' '..aoooanlnn _- . Q I O I I l; . o In ' ‘ w 1 p. UJh-J: --. ‘—‘ 220i . a’: i 22o '—— o. '5'!) i- .~ . n u "‘ y’ ° f; w. "c, non °°°o ‘Z . o 0 n "~-goc___ _ 20o _ _ 20o_ _. l; c . . gill!) I __ 180 . _. ._ 180 o ~_ .__ . a‘ O q ' $150 - __ 16o .' __ 160 o .' ___ I . ; o o _ g , - fleet _- Meat _' Meat ‘i 14o_ __ 14o ..__ no ‘ _- Ja ' -‘l > !§12o_ _ 12o__ __ 12o-_ _ v .2 _Y1oo_ __ 1oo_ - _ 1oo_ - _ so 11o. l cans _._ 843i -- 21o. 2 cans i BO.__ '. NO- 3 "m5 _._ @.._ i 60__ __ 60,__ __ 40 | i 4o n I 4o 1 1 1 1 1 Time in hours Time in hear; Time in hourg Chart 1. Heat penetration curves for No. 1, 2, and. 3 cans during- heating‘ at 15 pounds pressure before sealing. A lid removed as soon as the gauge returns to zero, liquid is seen to have j been drawn out of "the containers so that frequently only a small amount is left. Without an elaborate set up for recording temperatures inside a the containers, it is imp0s'sib1e to» know just when to stop the heating process so that this condition will not occur. The fourth method was found to be the most satisfactory. Cold or 5 cool meat, which is easy to handle, is packed into jars or cans. The uncovered containers are placed 0n a rack in a cooker containing boiling i water to within 2 inches of the top of the containers. (Glass jars must w} be set in cool water so that the temperature of the meat inside and the water outside does not differ enough to cause breakage.) The cooker flid is adjusted, tightening only one pair of clamps. The heat is turned l on full and time is counted as soon as a continuous straight jet of steam escapes‘ from the petcock (“flowing steam”). For No. 1 cans “flowing steam” should be maintained for 80 minutes, No. 2 cans 60 minutes, and No. 3 cans 90 minutes‘. For pint jars the time is 60 minutes, for quart jars 80 minutes. Tests have shown that by using this method ‘ the meat temparture is raised to around 200° F. (Figs. 2 and 3). This 8 BULLETIN NO. 635, TEXASHAGRIOULTURAL EXPERIMENT STATION I l I I l l I 240__ __ 240__ _._ 240__ __ 220__ ' Cooker ___ 22o__ Cooker __ 22o__ Cooker _ a OCQIOOOOODIOPO ' olfitlbfiikOOblillblbOfig ....¢..~.IOOQCOOOOOOOOOOIOQBOOCQIOQZQQOO o f. l." l . 2oo__ a . _ 3oo__ f __ 20o___,’ __ o , o . . , - q l I _ EWBO- , _. 180 ' g ' -- 180 ,, _ E o 0 c ,' U a ° '5 15°—- ,' —— 160 I _' -— 160 .' __ Q v ' , ' I? - ' u t ° ' 5 14o "°° __ 14o a _' Meat __ 14o_ Meat __ H . m . , 5120 ‘ , __ 120, ' __ 1zo_ . _,_, . a . \—4 q ; 100 ' __ 100 __ 1oo__ , __ . , . . 9Q__ No. 1 cans __ so; No. 2 cans ___ 3Q__ . no, 3 cans __ / 60__ _. s0_. .__ so._ . ,__ 40 1 | 40' | | 4o | I I 1 1 1 Time irrhours Time in hours Time in hours Chart 2. Heat penetration curves for No. 1, 2, and 3 cans during heating 1n steam before sealing. 240 I 240 I I Pint glass jars Quart 5'1,“ d," 220 _. c k .__ 220 ._. ._. °° 9r Cooker .OlOQIJOOOO i lfivililflfiiOod 20o __ , __ 20o _ __ ' . o _. " 9- 180 . .._ 1so __ .- .._. e Q ' F - a ' I _ ‘S 160__ __ 160_ ' _~ __ L? . - FL - E , _ s 1w -_ 14<>_ - _- _ I; E51; . ‘"8 § 12o . __ 12o _- - “t _ i, . .5 . - _ 10°» i 190 . ‘ F__ e0 __ so ' .' __ 4 f ' so _ so__ | I n I I | 1 1 Time 1n hours Time in hours Chart 3. Heat penetration curves for pint and quart glass jars during heating in steam before sealing? is high enough to insure an actual temparture as high as 180°F when processing is begun, if the meat is sealed quickly. This method of heating before sealing has several advantages. After “flowing steam” is obtained, the cooker needs no attention until the time is up——a decided advantage over using pressure, as on many ranges METHODS‘ FOR SAFE PROCESSING OF‘ HOME CANNED MEATS 9 flame needs frequent adjustment ‘to maintain even pressure in the ker and the pressure gauge must be watched constantly. The containers always full of liquid when the lid is taken off the cooker. The total e required with “flowing steam” is about the same as when pressure is v since a fair comparison must include not only the time under pressure » the 7 minutes allowed before closing the petcock, the time to reach desired pressure, and the time to return to zero (compare Figs. 1 2). The total time for No. 1 cans with pressure is 90 minutes, with wing steam” 60 minutes; for No. 2 cans with pressure ‘or “flowing m” 80 minutes; for No. 3 cans with pressure 100 minutes, with tgwing steam” 106 minutes. then steaming is done over a low flame on a gas or on a kerosene e, the time required to obtain “flowing steam” may be as much as .4... 3 hours. In such cases the time after “flowing steam” may be re- g d considerably (Figs. 4. 5, and 6). In fact, on an old model kero- e I. stove, the meat had reached the desired temperature by the time ‘wing steam” was obtained (3 hours). However, the conditions vary much among difierent stoves that no recommendations can be made; 1 temperature of 180°F when processing begins is higher than is- fre- _ ntly recommended but is practical if this method of heating before g is used and the cans or jars" are sealed quickly and replaced im- k tely in the hot cooker for processing so that the internal tempera- = of the containers does not drop below 180°F before processing ns. If the containers cannot be sealed as soon as “steaming time” | I I I I I 2 ' | I | Kerosene stove ‘ i ggqi L“ 5“ mam‘ ”,»onou ‘00000000001 o‘ - "i fiihat v l. Meet | . | | s | l 1 g 2p a \ g 1 Time in hours Time i“ h°“1'9 ' 4. Heat penetration curves for Ho. 1 cans during heating before sealing- on kerosene stove and over 10w gag flame. 10 BULLETIN N0. 6323, TEXAS AGRICULTURAL EXPERIMENT STATION 2 _ | i I I 2Q f ‘ I I zzqi Kerosene stove ___ 2;0___ 1-9" E55 5'15"" __ 2oo- a”.'~ —- 200- c", i“ f‘. ‘or. h‘ 180i "do j 180i ‘"9 .1 é cooker ‘g. Cooker r3", - é 1ec_ w“, -- 1s0-- "_- s- ,v . o n» ,8 E‘ 14C___ ‘.0000. ___ 140i " i r: .- ' ,3 f‘ .‘ Meat ' -' ‘b i i J -— E 120 x. Mes 120 ‘mow’. ‘E » l‘ "‘ 1oo__ -_ 100' —- 80: —— 3°—— '1 6Q__ __ wt I. - ___ "' L L I I I I I 1 3 1 2 Time in hours Tim? ill hwfi Chart 5- Heat penetration curves for No. 2 cans during heating before sealing on kerosene stove and over 10w gas flame. - 24 I I ‘ I I I 220___ Low gas flame __ "OQOOOQO 0 1' zoo-_- _,.-‘ . - 1‘. v 1eo__ _-" - _ s~ z 16o__ Cooker .,- ___ 3 v“ a ,0 1-. w . é 140_- _.' _ _. ~ ‘g9 .0 . ‘s w", .' q; 12o__e__.,,.~"’ W“ _ s -P g 10o. __ ac__ t» _. eo__ __ ......... .. I | _l | I 1 a s Time in hours Chart 6. Heat penetration curves for No. 3 cans temperature provided qooker (Fig. 7). during heating before sealing on low gas flame. the containers are left undisturbed in the closed METHODS FOR- SAFE PROCESSING OF HOME CANNED MEATS 11 0F I up QF I I llo. 1 cans No. 2 cans lio. 3 cans 21<1__ ._ 21Q__. i 21OL___ __ . -. P“... 20c " _ 20o - B 20o u» 5 B . —~ —- l... 3 "- o 0 A Q A nasal .. . .. , . 1so_ ., A _ 1eo._ ., ..,_ 190.. °.._ __ I I o 1w '. | 18o . | 180 | ' | Time in hours Time in hours Time in hours Chart 7. Cooling curves of cans under different conditions. A. On table ‘ at room temperature. B. Left undisturbed in closed 0001181‘. Heat Penetration Tests , The shortest safe processing period for ground meat in sealed cans _was tested in two ways. In the first, now to be described, heat penetra- tion data were obtained and used to calculate the time needed to de- stroy spores of Clostridium botulinum. Thermocouples and stuffing boxes for the pressure cooker, cans, and ~jars, were constructed for use in measuring heat‘ penetration. The di- rections given by Bigelow (2) were followed as closely as possible. At ‘first, the thermocouple readings were made with a Leads Northrup po- ten-tiometer and the millivolt readings converted into degrees centi- grade. Later, the work was" speeded up greatly by substituting for the potentiometer a Celectray recording device equipped with four thermo- couple lead wires which recorded the temperature on a chart. When this instrument was obtained, the thermolite rods through the stuffing boxes (recommended by Ball) were discarded because the asbestos cov- ering on the wires of the new apparatus prevented injury during tight- ening of the stuffing boxes. Two thermocouples were led into the pressure cooker by a shank type stufiing box attached to the lid. One of them was" short for determin- ing the temperature of the cooker, the other long and equipped with a flat type stuffing box for determining the temperature inside the can of meat. Since the lid on tin cans could not be sealed with the stuffing box in place, a small round hole was cut in the center of the lid of the test can to permit inserting the thermocouple after sealing. The flat type stuffing box could then be soldered to the lid, closing the ho-le completely. Soldering the stuffing box to the can of hot meat proved to be a very trying procedure. The heat from the soldering iron over- heated the contents at the top of the can forcing the greasy broth through the liquid solder. Unless this was removed completely, the solder would ‘not hold. Frequently a can, which seemed sealed when placed in the cooker, was leaking when removed from the cooker after processing. This necessitated many runs before data on a perfec-tly sealed can were obtained. This difficulty was not present in the trials with glass‘ jars. A square, wide mouth, glass jar having a glass top and screw band was used. A 12 BULLETIN NO, 635, TEXAS AGRICULTURAL EXPERIMENT‘ STATION hole was drilled in the glass top with emory dust and a shank type stuffing box was attached with gaskets and screwed tight, easily forming an airtight junction. Heat penetration tests were made at 15 pounds pressure f_or No. 2 tin cans and pint and quart glass jars, and at‘ 10 pounds pressure for No. 2 cans on a gas stove and on an old model kerosene stove. Results from Heat Penetration Tests Heat penetration data are given in Tables 1-3 inclusive. Safe processing periods were calculated from the heat penetration data by the National Canners Association, using the method developed by Ball (1). . (Such calculations are made routine-ly by the- National Canners Asso- ciation from data collected on industrial packs but previous to the time this work was planned they had not had access to such data on packs made according to home canning procedures.) ‘ With 15 pounds pressure. Heat penetration data for ground meat in No. 2 cans are given in Table 1. Calculations showed that the No. 2 cans would require processing at 15 pounds pressure for 50 minutes to destroy spores of Clostridium botulinum. v Heat penetration data were not obtained for No. 1 and No. 2 cans. Bigelow (2) gives a table of factors for estimating safe processing times Table 1. Heat Penetration Data for No. 2 Cans at 15 Pounds Pressure Temperature °O Time I in minutes Pressure Center ’ cooker of can 2 » l 9a 3 1011 4 102 5 107 7 K 113 9' 120' 10 121 11 121 13 121 15 121 17 121 19 121 22 121 25 121 28 1211 31 121 34 121 37 121 41 1211 45 121 50 121 55 121 6O 121 65 121 70 121 75 116 S0 110 R5 106 METHODS: FORI SAFE PROCESSING 01*‘ HO'ME CANNED MEATS 13 Table 2. Heat Penetration Data for No. 2 Cans at 10» Pounds PWSSHIQ Temperature °O Temperature °O g Time '1 ime iln minutes Pressure 1 Center in minutes Pressure (Tenter - cooker of can cooker. of can 0 52 89 641' 116+ 109 2 7s 1 s9 c6 115 109 4 1 s1 1 88+ es 115 109+ 6 1 93 88- 70 116 110 8 1 100 87 72 116 110+ 10 1 100+ 1 87 74 116+ 111 12 1o1— 1 87- 76 116- 111 14» 101 - 87 + 78 116- 111 + 16 103 88- 80 116- '- 18 10s 1 ss s2 11c- 112 2n 112 1 819- 84 116- 112 22 116 90- ~ 8'6‘ 116- 112+ - 24 116- 9'0 88 116 113 26 ___ 92 90 116 113 28 116- 93! 9'2 116 11% 30 116- 9'4 9'4 116 113+ 32 * 116- 95 96- 116 114- 51 116 97 9'8 116 114- ss 11c 1 es- 100 11c 114- 38 116 99- 102 116- 114- 40 116 100- 104 116- 114 42 116 1 100+ 106 115 114 44 116 1 102 108 115 114 46 110 l 103 110 115 114+ 48 116 i 1% 1121 116 114-1 :30 116 1 104 114 116 114+ , 52 116 1 105 116 116 115- 54 116- ‘ 106- 118 116 115- 56 116- 1 107- 120 ~ __- 58 116- 107 122 116- 115+ 60 116- 108- 124 101 105 62 116+ 109- 126 i --- 100 u various sizes of cans, if the correct time for one size is known. Mul- plying the Bigelow factor 1.5 by 50 (the processing time required for o. 2 cans) gives an estimated processing period of 75 minutes for No. cans. The Bigelow factor 0.6 times 50 gives an estimated processing riod of 30 minutes for N0. 1 cans. ' Heat penetration data for ground meat in pint and quart glass jars ere obtained but the National Canners Association was swamped with iergency measures when these data were ready. Since the volumes of se jars are similar to No. 2 and No. 3 cans respectively, they were umed to require similar processing times. Glass heats more slowly if tin but tin cans are cooled quickly and thoroughly in cold water ediately after processing, while glass jars are allowed to cool slowly the cooker until bubbling stops then the cooling is continued in air room temperature. Since the heat penetration tests showed that the iperature inside the glass jars when the pressure gauge returnedto no was 106°C or 107°C (corresponding to about 4 pounds pressure), - slow cooling would allow further sterilization to take place. This ow, cooling is" not practiced in commercial canning and the formula id for calculating safe processing times makes no provision for in- ‘ding this part of the sterilization period. Calculated processing peri- 14 BULLETIN NO..635, TEXAS AGRICULTURAL EXPERIMENT STATION Table 3. Heat Penetration Data. for No. 2 Cans at 10 Pounds Pressure o-n an 01d Model Kerosene Stove Temperature °0' Temperature “o Time _ Time in minutes Pressure Center 1n minutes Pressure Center ' cooker of can cooker of can 0 60 844+ 88 112 102+ 2 7'3 84- 90 112+ 103 4 77 83 92 3 104-- (i 80 82 94 114- 104 8 812 81 96 114 105 10 84 $1 — 98 114+ 105 12 86- 81- 100 115 106 14 87 — 80+ 102 115 107- 16 819‘ 80+ 104 116- 107 18 90- 80 106 116- 108 20 9'1 80+ 108 116— 108 22 9'2 80+ 110 116- 108+ 24 93 81 11:2 116— 109 26 9'3 81 114 116 1091+ 28 9'3 82 116 116 110 30 94+ 8421+ 118 116 111 — 3.2 95 83 120 116+ 111 34 9'6 8&4 122 116+ 111 36 97 84 124 116 112- 38 9'8 814+ 126 115 112 44) 99 85 128 115 1121+ 42 99+ 86 130 115+ 113- 44 100 87 132 116- 113- 46 100 88- 134 116 113- 48! 100+ 88+ 136 116 113 50 100+ 819+ 138 116 113 52 101 90 140 116 113+ 514, 102 _- 142 116 - 114 56 102+ 91+ 144 115 114 - 58 104- 92 146 115 \ 114 e0 104 93 14s 115 l 114 62 105 94- 150 115 l -__ 64 1051+ 94+ 152 115 114 so 10c 95 154 115 | 114 68 107 96 156 116 — 114 70 108- 97- 158 116— 114+ 72 108 97 160 116 114+ 74 109‘- 98 162 116 114+ 75 109 99+ 164 116 114+ 78 110- 166 116 114+ so 110 1001- 16S 116 115- 82 111 - 101- 170 116 115 84 111 101 172 100 115 s6 112- 102 , ods based on heat penetration studies of meat canned in glass jars, there- fore, would be somewhat higher than the minimum. i With 10 pounds pressure. Heat penetration data for ground meat in No. 2 cans are given in Table 2. Calculation showed that 100' minutes would be needed for safe processing. Heat penetration data using an old model kerosene stove are given in Table 3. Such stoves are sometimes used on Texas farms and ranches to provide supplemental heating units when large amounts of canning must be done in one day. The laboratory experience was similar to that in the homes. It required 21/2 hours to reach 10 pounds pressure even with the water in the cooker boiling when the sealed cans were set in. (On such a stove 15 "pounds pressure is exceedingly difficult to METHODS FOR- SAFE PROCESSING OF‘ HOME CANNED MEATS 15 attain.) Although the slow rate of heating for the cooker was reflected in the rate of heat penetration into the meat in the sealed cans, yet at the time 10 pounds pressure (116°C) was reached in the cooker, the meat was actually at a higher temperature (109+°C) than When the gas stove (90—°C) had been used (compare Tables 2 and 3). This would seem to indicate that less than 100 minutes at 10 pounds pressure would destroy the spores of Clostridium botulinum when a kerosene stove is used. But when the data were submitted to the National Canners As- * sociation they reported that this method of processing was “impractical,” and did not give any calculated processing time. Other reasons‘ (given later) also caused the authors to agree» that no recommendations‘ should be made for this type of process. Inoculation Tests Since the deadly toxin of Clostridium botulinum is produced when vi- able spores grow inside the sealed cans, the processing time must be long enough to destroy the viable spores. Inoculation tests should give this information but it is difficult to produce spore crops of strains of Clostridium botulinum having a high resistance to heat, even a medium resistance being difficult of attainment. Esty and Meyer (3) reported the maximum heat resistance of spores artificially produced under the most favorable conditions for growth and heated in a phosphate solu- tion at pH 7.0 was: 4 minutes at 120°C (248°F') 10 minutes at 115°C (239°F) 32 minutes at 110°C (230°F) 100 minutes at 105°C (221°F) 330 minutes at 100°C (212°F) Yet the knowledge of the maximum resistance in meat of naturally oc- curring spores is of major importance in determining adequate steriliza- tion' processes. As a result another organism was needed similar in its growth requirements to Clostridium botulinum and at the same time having the ability more readily to produce spores of comparatively high heat resistance. Townsend, Esty, and Baselt (10) made heat resistance studies on spores of putrefactive anaerobes to determine safe processes in canned foods. They reported that P. A. No. 3679 was the most suit- able organism yet found as a substitute for Clostridium botulinum and “processes for canned foods based on spoilage data obtained by the use of suspensions of No. 3679 of a resistance in phosphate equivalent to the maximum for Clostridium botulinum should be on the safe side for Clostridium botulinum.” The organism has since been widely used l by laboratories connected with the canning industry in experiments 0n canned foods. It was the organism used in this study. The spore sus- pension was obtained from the National Canners Association. l6 BULL-ETIN NO. 635, TEXAS AGRICULTURAL EXPERIMENT‘ STATION Four processing periods for each size of can or jar were used in thef inoculation tests to provide at‘ least one pack above and one below the“ lowest point at which viable spores would be found. (This point had. been determined previously by calculation from heat penetration data, or by other ways of estimation). Control cans or jars which were not‘ inoculated were processed in each cooker with the inoculated ones. In- oculations were made with a suspension containing 10,000 spores per milliliter. For No. 1 cans 0.5 ml. was used, No. 2 cans and pint jars.” 1 ml., No. 3 cans and quart jars 1.5 ml. After heating but just before ' sealing the spores were placed in the center of the cans and jars with a.“ i pipette. Inoculation at this point made certain that all of the spores; remained in the container. Inoculation before the steaming period, would have raised the question of whether or how many spores were, lost‘ in the meat juices which spilled out of the full container during the _ < handling necessary for “sealing. I After processing, the tin cans were cooled quickly in cold water but; A the glass jars were allowed to cool in air at room temperature. All of, the cans and jars after cooling over night to room temperature were; stored at 95-98°F. Those that showed no external evidence of spoilage (bulging or vis? ible gas bubbles) after several months of storage were cultured in the. laboratories of the Division of Veterinary Science to determine the Dres- ence of viable spores. The test for viable spores was carried out as A follows: DeXtrose-meat-mash media was placed in long narrow tubes. (20 x 200 mm), heated just prior to inoculation to drive off any oxygen that might be present and cooled rapidly to 35°C. Control tubes of this medium, using unheated spores of P. A. No. 3679, showed luxuriant growth as evidenced by gas formation, clouding of the supernatant fluid, and a marked offensive odor. The containers of meat were opened asep- tically. One milliliter of meat particles and broth was placed deep into the tubes containing the media, care being taken to introduce not air . bubbles at the time of transfer. Short lengths of sterile glass tubing were used as pipettes in making the inoculations. All tubes were held in the incubator at 37°C for 7 days before being discarded. However, the positive chltures usually showed up within 24 to 48 hours, only one showed up as late as 72 hours. Since the processing period at 10 pounds pressure as calculated by the National Canners Association was 100 minutes the method using 10 pounds pressure was considered impractical under home canning condi- tions and no inoculation tests were made. No inoculation tests were made in cans processed on the kerosene stove. Each kerosene stove would present a difierent problem and it was deemed impossible to make recommendations which would apply to _ each. METHODS‘ FOR SAFE PROCESSING OF HOME CANNED MEATS 17 Results from Inoculation Tests When spores from P. A. N0. 3679 were used,_ the data (Table 4) show t using a temperature as high as 180°F‘ When processing begins and rocessing pressure of 15 pounds, the lowest point at which viable res were absent is: 40 minutes for No. 1 cans; 50 minutes for N0. 2 75 minutes for No. 3 cans, 50 minutes for pint jars and 65 minutes uart jars. These are the lowest safe processing times for canned nd meat as determined in this study. ble 4. Spoilagefilfests of Canned Meat Processed at 15 Pounds Pressure No. of cans No. of cans containingviable spores Prooess- stored Length N0. of ing ———-—-———— oi Inoculated cookers time storage Cion- ' tull min- Gon- Inocu- at 98°F trols Positive Per- utes trols lated (3’T°O) Spo on Total cent- culture age Tin Cans Bulged 1 20 12 24 1 wk. 0 24 ..- 24 100 1 30 12 24 3 mo. 0 0 2 2 8 1 40 12 24 _ 3 mo. 0 0 0 0 0 1 50 12 23 3 m0. 0 t 0 0 0 0 2 30 8 22 5 m0. 0 10 11 21 9'5 2 40 8 24 5 mo. 0 0 5 5 21 2 50 9 23 5 m0 0. 0 0 0 0 2 60 10 22 5 m0. 0 0 0 0 0 3 9 21 2 mo. 0 4 9 13 62 3 65 9 21 2 mo. 0 0 4 4- 19 3 75 9 21 2 mo. 0 0 0 0 0 3 1 9 21 2 m0. 0 0 0 0 ' Glass Jars Bubbles 2 30 8 18 2 mo. 0 0 12 12 67 2 40 9 20 2 mo. 0 0 2 2 10 2 50 9 16 2 mo. 0 0 0 0 0 2 60 10 16 2 mo. 0 0 0‘ 0 3 55 6 15 3 mo. 0! 0 2 2 ‘ 13 5 65 10 23 3 mo. 0 0 0 0 0 5 75 9 22 3 mo. 0 0 0 0 0 4 85 8 20 3 mo. 0 \ 0. 0 0 ‘ 0 Discussion mparisons were made between the calculated processes and those ined by inoculation te-sts. For No. 2 cans the National Canners iaiion had calculated from heat pentration data that 5O minutes ‘d, be required to kill the spores of Clostridium- botulinum, inocu- _ w tests showed that‘ 50 minutes was the lowest period at which no 1o spores were found. For No. 3 cans the estimations using the 18 BULLETIN NO. Q35, TEXAS AGRICULTURAL EXPERIMENT‘ STATION Bigelow factor gave 75 minutes and 75 minutes was the lowest process- ing period at which no viable spores were found in inoculation tests. However, for No. 1 cans the estimations using the Bigelow factor gave 30 minutes but the inoculation tests showed that 40 minutes was the lowest processing period at which no viable spores were found. Experience showed that in some of the glass jars the seal was broken when the jars were removed from the cooker. Heat penetration tests showed that when the cooker was opened after processing, the tempera- ture inside the glass jars corresponded to about 4 pounds pressure. This pressure, seemed sufficient for a sudden jar to cause the softened rubber to bulge outward and break the seal. For this reason it is rec- ommended that the glass jars be allowed to remain undisturbed in the open cooker until the liquid inside stops bubbling. Then they may be removed and the cooling finished in air at room temperature. When processing times are to be recommended to the homemakers the minimum periods necessary to destroy spores of Clostridium botu- linum must be taken into consideration. However, since it is difficult under home conditions to know when Slight inaccuracies occur in the pressure gauge, it seems wise to recommend the use of processing periods‘ 10 minutes longer than those found to be the minimum. The following factors of safety are present in the recommended processing times: 1. Heavy inoculation of viable spores. 2. Since spores were placed in cans or jars“ after steaming and just before sealing, they were not subjected to the heat treatment involved in “heating “before sealing” which might have made them somewhat more susceptible to the higher temperature later. 3. Actual spoilage of meat in the cans was not‘ found at a level twenty minutes under the recommended level. 4. . Viable spores were not found at a level ten minutes under the rec- ommended level. It should be noted also that the toxin of Clostridium botulinum is thermolabile, the toxic properties being destroyed at 80°C (176°F) in 30 minutes. Thus if the canned meat is thoroughly heated just before it is eaten, any toxin present will be destroyed. Hall (4) who reported details of several cases of botulism observed from his st'udies'that there seem to be three distinct groups of house- wives: 1. Those who are well grounded in the fundamental principles of. bacteriology as applied to home canning; who intelli- gently use controlled steam pressure; who are ever con- scious of the danger of botulism in spoiled canned foods; and who always recook all canned foods before serving them. These housewives and their families rarely, if ever, die from botulism. ' i 2. A very large number of women who have little or no knowl- edge of bacteriology; who use antiquated “cold-pack” or other inadequate methods of canning; and who having much spoilage, are vaguely conscious of an ill-defined ele- METHODS FOR» SAFE PROCESSING OF HOME CANNED MEATS 19 ment of danger which they attempt to avoid by tasting each jar of food before serving it. N0 doubt thousands of jars of perfectly harmless spoiled home canned foods are dis- carded as a result of this common practice, but from time to time a jar is encountered which contains botulinus toxin resulting in the death of the human guinea pig and often domestic fowls and other animals as well. In these cases the other members of the family generally do not suffer. 3. The third group consists of people who are at the bottom of the ladder educationally, socially, and economically; who use the crudest methods of home canning; who seem to be oblivious to the danger of eating spoiled foods; and who will apparently eat anything that looks like food if they can get it down. Such foods may be highly seasoned or flavored to mask spoilage. When botulism occurs under such conditions it usually takes a toll of several lives. Research in home canning therefore must be aimed to benefit home- FInakers who are capable of following directions" carefully, such as those the first group mentioned by Hall. It would be impossible to make recommendations for the third group because of the uncertainty any of them would be followed. \ ACKNOWLEDGMENT kit;- Grateful acknowledgment is made to the National Canners Associa- fflon for calculating the processing times from the heat penetration data 31nd for supplying the spore suspension of the test organism. SUMMARY AND RECOMMENDATIONS x Two periods of heating are necessary in canning meat; the first before gsealing, for driving the air out of the cans or jars to provide a partial ‘vacuum inside the sealed cans and the second, after sealing, for destroy- ‘ ing spoilage organism inside the sealed cans. The Texas Agricultural QExtension Service has, heretofore, recommended that both periods of i {heating be under pressure. Because of certain difficulties, experiments wvere set up to determine 1. an adequate but simpler procedure for ffheating before sealing, 2. the shortest processing time which would igfjnciestroy the spores of Clostridium botulinum. These tests Were carried gout by using heat penetration data and by placing live spores inside the écontainers of meat before processing. If heating before sealing is done under pressure, the cooker needs to watched constantly. Some- liquid is always drawn out of the con- Ftainers which then need to be refilled before sealing—a messy and time Yconsuming duty. Meat heated in boiling broth, in deep fat, or in an [oven must be packed while the meat is hot and difficult to handle. .There is danger that the meat temperature will fall below 180°F before fsealing. The method of heating in steam before sealing was‘ found to be ;_bést. It lfas the following advantages: containers are packed with cold meat which is easy to handle, containers need only to be sealed after 20 BULLETIN NO, 635, TEXAS AGRICULTURAL EXPERIMENT STATION heating so that it is easy to have the meat temperature as high as 180°F when processing begins, the cooker is not under pressure and therefore does not ne-ed constant watching. ' ' The shortest safe processing period for the sealed cans was tested in several ways. 1. By using the heat penetration data t0 calculate the time needed to destroy the spores of Clostridium botulinum. The-se calculations were made by the National Canners Association according to a complicated mathematical formula previously worked out and tested under commercial canning conditions. 2. A short method of calculating Was used after the safe processing period had been determined for one size of can. 3. The calculated processing periods were then checked by using cans of meat inoculated heavily with spores of P. A. 3679, an organism whose spores are similar to those of Clostridium botulinum in heat resistance but are more uniform in their high heat resistance. The containers were processed at four ‘different time levels for each size of . jar or can so that at least one pack would be above and at least one below the point at which no viable spores were present. Growth of the ~ organism took place at the lowest level in the cans causing them to bulge. A foul odor which was unmistakable was present also. With a longer period of processing no spoilage too-k place but viable spores were pres- ent in a small percentage of the containers. No spoilage was observed in any of the glass jars but viable spores were found at the lowest levels. With the two or three still longer processing periods no viable spores ; were found. The lowest level at which no. viable spores were found is considered the lowest safe processing period, but ten minutes is added to it as a factor of safety in making recommendations. The two heating periods recommended are: “Steaming time” (heating before sealing) No. 1 cans‘ 30 minutes _ No. 2 cans 60 minutes _ No. 3 cans 90 minutes Pint jars 60 minutes Quart jars 80 minutes “Processing time” (in sealed containers at 15 pounds pressure) No. 1 cans 50 minutes No-. 2 cans 60 minutes No. 3 cans 85 minutes" Pint jars 60 minutes Quart jars 75 minutes When “steaming time” is over, seal immediately, put hot sealed con- tainers innnediately into a hot pressure cooker, and begin processing as quickly as possible. This assures a temperature of 180°F inside the containers when processing begins. When the pressure on the gauge returns to zero, cool the tin cans quickly and thoroughly in cold water but allow the glass jars to remain‘ undisturbed in the open cooker until the liquid inside stops bubbling,, then finish cooling in the air at room temperature. METHODS‘ FOR SAFE PROCESSING OF HOME CANNED MEATS 21 REFERENCES , C. 0. 1928. Mathematical Solution of Problems on Thermal Proc- “Health 115-245. low, W. D., Bohart, G. S., Richardson, A. C., and Ball C. O. 1920. eat Penetration in Processing Canned Foods. National Canners Asso- ciation Bulletin No. 16-L. - , J. R., and Meyer, K. F. 1922. The Heat Resistance of the Spores of B. zfiogggniiég and Allied Anaerobes. XI. Journal of Infectious Dis- ses : - . a Ivan C. 1936. New Outbreaks of Botulism in Western United States. Food Research 1:171-198. . er, R. A. 1927. Manual of Veterinany Bacteriology. The William d Watkins Co., Baltimore, Md. er, K. F., and Dubovsky,. B. J. 1922. The Distribution of B. Botulism in California. II. Journal of Infectious Diseases 31:541-555. ley, Grace I. 1940. Canning Meat in the Home. Texas Extension rvice Bulletin B-101. Y> on, Casper. I., and Knowles, Darlene. 1940. Effectiveness of Heat enetration in Meat Canned in Glass Jars in a_ Pressure Cooker. Jour. lgri. Research 61:753-759. - ley, L. and Stienbarger, M. C. 1936. (New edition 1942.) Home ning of Fruits, Vegetables, and Meats. Farmers’ Bulletin 1762. - send, C. 'l‘., Esty, J. R., and Baselt, F. C. 1938. Heat Resistance . tudies on Spores of Putrefactive Anaerobes in Relation to Determina- Ttirn of Safe Processes for Canned Foods. Food Research 3323-346. easing of Canned Food. Uniirersityiof California Publications in Public -