This is Fourth edition tech levels. For Third Edition the tech level would be C or better.
Below is a general breakdown of food preservation:
Ancient
Pickling
Drying
Curing (salt)
Sugaring
Smoking
Jellying
Jugging
Freezing (1)
1820
Canned
1880
Refrigeration
Pasteurization
1920
Freezing (2)
Vacuum forming
1950
Preservatives
1960
Irradiation
1980
Modified atmosphere
2000
Electroporation
Pascalization
(1) In latitudes that allowed for winter freezing of food.
(2) Industrial freezing
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