Monday, February 24, 2014

CHEF TALK Retort and the Culinary Consequences Part 1


Retort and the culinary consequences

Unlike ‘Pasteurized’ cooked meat products where the survival of heat resistant micro organisms is accepted, the aim of sterilization is the destruction of all contaminating bacteria including their spores. Heat treatment must be intensive enough to inactivate/kill the most heat resistant micro organisms, which are the spores of Bacillus and Clostridium.
If spores are not completely inactivated, vegetative micro organisms will grow from the spores as soon as conditions are favorable again. Favorable conditions exist when the products are stored at ambient temperatures.
Temperatures above 100 degrees Celsius, usually between 100 degrees Celsius to 121 degrees Celsius are needed to achieve this goal depending on the product. These temperatures must be reached inside the product.
Surviving micro organisms can either spoil preserved meat products or produce toxins which cause food poisoning to consumers.
Clostridium is more heat resistant than Bacillus. Bacillus spore will die at 110 Celsius. Clostridium spores need 121 Celsius to be inactivated within a short period of time. If these temperatures cannot be reached within a given time, a longer time period must be applied.
From the microbial point of view it would be ideal to employ very intense heat to eliminate any form of micro bacterial activity in meat products. However, most meat products cannot be exposed to such intense heat without suffering.
Degradation of their sensory quality, such as very soft texture, jelly and fat separation, discoloration and undesirable taste will occur.
Loss of nutritional value, destruction of vitamins and protein structures will arise as well. Vitamins are hardier to heat than bacteria but not resistant to intense heat of this nature. In order to comply with the above aspects a compromise has to be found.
Sterilization must be intense enough for micro biological safety and moderate enough from the product quality point of view.

It is of extreme importance that products, meant for canning, that are of a mixed composition (meat and vegetables) are being exposed to a temperature of 121 Degrees Celsius. If not, these products will be exposed to undesirable bacterial growth at ambient temperatures.  
Retort pouches, which are containers made of aluminum or plastic coated nylon material are of growing importance in food preservation.  Thermo-laminated food pouches have a seal layer made of PP (Polypropylene) or PP – PE (Polyethylene) Polymer and the outside layer is usually made of nylon. They can be used for ready to eat meals, and sausages in brine.
The need for safe but not excessive heat treatment received in products needs some practical consideration. These are: Heat treatment temperature and heat treatment time. Different temperatures need different treatment times.
The high temperatures are achieved by injecting steam under pressure in specialized retort steam kettles. Sometimes a combination of boiling water and pressured steam is used.
The level of heat treatment received by a product is measured in the value F. F 1 means an exposure at 121 Celsius for 1 minute at the coldest point of the product. By F 2 this is 2 minutes and so on. The level of sterilization of a product can herewith be determined.
Complete safe canned products, pathogen free and no spoilage, should be produced with temperatures between F 4.0 to 5.5 with temperatures ranging between 110 and 130 Celsius. This will provide a shelf life at ambient temperatures of up to 4 years at storage temperatures below 25 Celsius.
In part 2 of this article I will have a closer look at the possibilities of applying retort in home cooking and some aspects of retort in the culinary world.      

Written for PMG by:

Professional Chef
Marinus Hoogendoorn
Culinary expert in recipe development   

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