Hot Filling is a proven and recognized method for filling high acid foods (pH less than 4.6) that will be shelf stable at ambient temperatures. Now a days, this method is used extensively in the food industry for filling a glass and plastic containers and in paperboard cartons. It relies on heat treatment to temperatures in the region of 194-203 °F (90-95 °C) for at least 15 seconds (typically 15-30s). This process produces a “Commercially Sterile Product” by killing all microorganisms capable of growing in it. The product is then cooled and filled at temperatures ranging 180-185 °F (82-85 °C) into containers, sealed immediately with closures, and then held at this temperature for approximately 2-3 min. The hot filling will sterilize the inner surface of the container. The filled containers are usually placed on their sides so that the neck-finish and closure are also sterilized. The containers are then cooled in a cooling tunnel in order to minimize the thermal degradation of the product.

The main purpose of hot filling is to provide a product free from microorganisms capable of growing in it at ambient storage. Commercial sterility or thermally processed food refers to the absence of disease-causing microorganisms, absence of toxic substances and of spoilage-causing microorganisms capable of multiplication under a number of non-refrigerated storage and distribution conditions.

The properties of the food will largely determine the sensitivity to spoilage by microorganisms. Temperature and water activity are important factors that affect the microbiological spoilage of foods. Another factor of major importance for the growth and survival of microorganisms in foods is the pH or acidity. Low pH (high acidity) will restrict a number of microorganisms from growing and spoiling the food. It is, therefore, very important to know the acidity of the food when deciding the process conditions and the possible shelf-life of the product. Foods are often divided into two main groups in terms of their acidity: high acid foods with pH 4.6 or lower and low-acid foods with pH higher than 4.6.

There are some important reasons for the acidity classifications:

• Most spores that may survive heat treatment and chemical will not grow or germinate at pH lower than 4.6.
• Pathogenic bacteria will not grow at pH lower than 4.6
• The sensitivity to heat treatment is increased at lower pH.

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(Source: petmachine.in)