Autoclave Research Papers - Academia.edu (original) (raw)

The heat penetration factor fh is crucial in calculating the pasteurization or the sterilization time of packaged foods. This document explains how to calculate, or estimate, the heat penetration factor fh. Each explanation is... more

For a quick reference, the second page gives an overview of the main factors which affect the heat penetration factor fh. It presents the equations to calculate the fh, and lists formula to convert a known fh to the new fh after a change in processing or packaging conditions.

Chapter 1 shows the basic equations to calculate the heat penetration factor fh of a packaged liquid or solid food. How this fh factor can be used in heat processing, is illustrated by a sterilization process calculation.

From tables with fh values in Chapter 2, a first rough estimation can be made of the heat penetration factor fh of a food product, packaged in a cylindrical metal can.
To use these tables, you need to know the product texture (solid or liquid), the packaging size (length L; diameter D), the retort conditions (rotation or still retort) and the heating medium (saturated steam, showering water, or full water).

Chapter 3 outlines the effects of the food packaging on the heat penetration factor fh: the material of the packaging (metal or glass); the shape of the packaging (cylindrical; brick; oval; cube; ball), and the packaging dimensions (length, height, width, etc), expressed as specific surface S (for a liquid food), or adapted squared specific surface S*^2 (for a solid food), are included in the equations of the fh.

Tables of the partial heat transfer coefficients for several types of retorts, food textures and packaging materials, and equations to calculate the overall heat transfer coefficient U, are presented in Chapter 4. A list with the estimated overall heat transfer coefficients U for all types of packaged liquid foods may be of help in rapid calculations of the heat penetration factor fh. For packaged solid foods, not the overall heat transfer coefficient U, but the thermal diffusivity a (many data in Annex 3), or the thermal conductivity k of the solid is required.

Excel spreadsheet “Heat penetration factor fh calculations.xls” simplifies the tedious calculations of the specific surface of a food container, required to find its heat penetration factor fh. Chapter 5 explains, by means of 2 worked examples, how to use this spreadsheet to estimate the fh of both a packaged liquid food and a packaged solid food.

Several foods consist of solid food pieces, submerged in a liquid, or in a watery brine. Examples are beans in brine, sausages in brine, meat balls in gravy, etc. Chapter 6 lists equations how to calculate the heat penetration factor of such foods: first calculate the heat penetration factor of the container filled with brine only, and then add the calculated heat penetration factor of the largest solid piece of the food.

If the heat penetration factor fh of a packaged food is known, and the company wishes to change the packaging size, Chapter 7 presents size correction factors to calculate the new heat penetration factor. The size correction factor is proportional to the container’s specific surface S for liquid foods, and proportional to the container’s adapted squared specific surface S*^2 for solid foods.

Chapter 8 presents packaging material correction factors for fh, in case a company intends to change the packaging material from metal to glass, or from glass to metal. The material correction factors depend also on the texture of the packaged food: solid or liquid.

Chapter 9 explains step-by-step how to obtain, from experimental heat penetration data, the penetration factors fh and fc, and the lag factors jh and jc. The experimental time-temperature data are used to construct a semi-log heating and a semi-log cooling graph, from which fh, jh, fc, and jc can be deduced. This data analysis is illustrated by an extensive example calculation, and concluded by a worked example.