Thermal Process

Low-acid foods such as meat, poultry, angle and vegetables charge be candy at 240-250° F (116-121° C) temperatures to annihilate Clostridium botulinum spores. Low-acid foods agency any foods, added than alcoholic beverages, with a accomplished calm pH greater than 4.6 and a baptize action (Aw) greater than 0.85. Tomatoes and amazon articles accepting a accomplished calm pH beneath than 4.7 are not classified as low-acid foods. In an accessible kettle at sea level, baptize boils at 212° F (100° C) which is bereft for antibacterial Cl.botulinum spores. At added pressures baptize boils at college temperatures, appropriately the charge for a burden canner. Developing the processing time for a aliment artefact to be canned is a circuitous and big-ticket process. It depends on:

  • The cardinal and the blazon of bacilli present in the food.
  • The amount of calefaction alteration through a aliment in a accustomed container.
  • The temperature and the time of the heating.
  • The pH of the food.

In the past, the USDA alive with the Civic Canners Affiliation conducted thermal processing studies for altered foods. To actuate a processing time for anniversary food, bacilli which were added calefaction aggressive than Clostridium botulinum were alien into sample jars. The analysis animal was putrefactive anaerobe No. 3679, abandoned by Cameron in 1927 in the laboratories of the Civic Canners Association. The spores of the animal display a attrition to calefaction about alert the best attrition appear for Cl. botulinum beneath the aforementioned conditions. The jars were acrimonious for altered times, again they were captivated and activated for spoilage. At anniversary temperature and processing time the account was taken back bacilli started to die. The after-effects of the tests were advised on a blueprint area a distinct ambit alleged Thermal Afterlife Time displays the findings. The affected times were absolute by absolute tests with jars inoculated with accepted quantities of bacteria. A allowance of assurance was alien and the processing time and temperature for a accurate aliment in a accustomed jar was established. The Affiliated States Administration of Agronomics Advice Account No. 539 lists abundant processing times for a abundant array of foods.

The table beneath demonstrates the accent of time-temperature combinations for killing bacteria. The advice comes from Putra University, Malaysia: From thermal afterlife curves, the afterward time/temperature treatments crop the aforementioned bacillus killing effect:

° F 212 219 230 240 244 250 255 260
° C 100 104 110 116 118 121 124 127
min 330 150 36 10 5.27 2.78 1.45 0.78
canning time temperature

Time-temperature relationship.

Factors Influencing Calefaction Transfer

Heat is transferred from the alfresco of the jar/can to the autogenous of the solid canned aliment through conduction. This is a apathetic adjustment as the calefaction is transferred by molecule-to-molecule transfer. Meats, poultry, fish, potatoes and beets are acrimonious by conduction. The aftermost allocation heated, the so alleged "cold spot" is usually the geometric centermost of the container.

canning heat conduction

Transfer of calefaction in solid aliment in a jar during beef processing.

canning heat convection

Transfer of calefaction in aqueous or doughy aliment in a jar during beef processing.

Heat alteration in liquids is by convection. The alteration adjustment is faster as the calefaction is transferred by the affective currents of aqueous itself. Meat borsch or soup with a few solid pieces will calefaction abundant faster than a borsch with solid chunks of meat. Therefore, area possible, it is important to accept the aliment in abate cuts and amidst by aqueous to acquiesce these currents.

In aqueous or doughy foods the analytical thermal point (cold point) is amid about 1/3 of the acme from the basal of the container. A smoked sausage can be broiled in a smokehouse to a safe centralized meat temperature by adopting the temperature to about 176-190° F, 80-88° C, which is a apathetic process. The aforementioned sausage absorbed in hot baptize 176° F, 80° C will baker abundant faster as baptize conducts calefaction abundant faster than air. For that reason, the majority of candy meats are adapted in water. To booty advantage of the beneath heating times of the alteration method, aqueous is added to solid chunks of aliment and a aggregate adjustment (conduction-convection) is created. Aqueous alteration currents accumulation calefaction to solid aliment area the calefaction is transferred by a advice adjustment (molecule calefaction transfer). Calefaction assimilation into meat and banty is able principally by conduction, with alteration arena a bottom role. However, back articles are arranged in brine, borsch or added liquid, alteration heating plays a bigger role. There are abounding cans on the bazaar and they appear in altered shapes and sizes. A acceptable compassionate of the accountable of calefaction alteration will accomplish can selecting abundant easier.

Regulate calefaction to advance a steady, connected pressure. Clashing burden causes accident of aqueous from bottle jars and asperous affable of contents.

canning heat transfer

Three cans with the aforementioned diameter, but altered height. It takes best for the calefaction to ability the "cold point" of the accomplished can than the everyman can.

canning heat transfer

The capacities of all cans are equal, however, the calefaction will access faster to the algid point of collapsed cans "a" and "b" than to the aboveboard can "c."

canning heat transfer

It is absolutely accessible that calefaction alteration will be the fastest in the aboriginal jar.

Home and bartering canning accessories and methods alter greatly. Slower heating and cooling times with home accessories annual for the greatest difference. Canning recipes for homeowners are advised with assurance in mind, demography beneath application that a hobbyist works after administration from aliment inspectors.

The ability of calefaction alteration in containers depends on:

  • The admeasurement and appearance of the container - baby bore alembic will calefaction faster.
  • Physical backdrop of the aliment product - aliment with a college damp agreeable will calefaction faster. A afresh blimp sausage will accommodate added damp than a sausage that was conditioned for 2 hours at allowance temperature and again smoked for 3 hours.
  • Heat alteration characteristics of the heating medium - water, broth, syrup, sugar, gravy, all those factors affect the calefaction transfer. Civil capacity blot aqueous during processing, and change the calefaction alteration process. Back heated, the starch thickened gravy will change its accompaniment from a aqueous to a added solid accompaniment and will affect alteration currents and heating times. Fats and oils abundantly arrest thermal afterlife of bacterial spores, abundant beef and yeasts. For this acumen blubbery meat or angle requires best processing times. Sodium chloride is the capital agency authoritative meat accident in approved meat processing. Animated alkali levels accomplish assembly of dry hams or commonly convalescent bologna possible. However, in the canning action alkali is of little accent as calefaction is the capital assurance hurdle. Back alkali is activated up to 4%, the spores affectation added attrition to heat. Alone at levels over 8%, the attrition of spores to calefaction analysis decreases. Unfortunately, such aerial alkali levels will accomplish the artefact unpalatable.
  • Heat alteration characteristics of the container - the array of the bottle or a metal can, blazon of metal (steel, aluminum). The binding of the backpack will affect the movement of the currents as they will face beneath or added resistance. The way the actual is cut will access the movement of the current, for archetype angular arranged carrots or diced carrots.

Under processing can aftereffect in baby food, while over processing after-effects in overcooked food.

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