In 1923, C. Olin Ball proposed a formula method which would allow for the extrapolation of process time independent of a required direct thermocouple measurement once time and temperature data were collected by direct measurement (heat penetration test). This mathematical calculation procedure is known today as the "Ball Formula Method" and is the most widely used method in the United States for both process evaluation and process design for retorted canned foods.
The Ball Formula method uses heating factors to calculate process times. These Heating Factors are generated from the evaluation of heat penetration test data. The time/temperature data for each thermocoupled container is plotted on an inverted semi-logarithmic graph, which is developed based on the Retort Temperature and the Come-Up Time experienced by the test containers during the heat penetration test. Heating Factors are derived from the graphed data for each thermocoupled container. The factors from a single container are chosen by the process authority for use in the Ball Formula, along with the desired Retort Temperature, Product Initial Temperature, and Fo value. The resulting calculated thermal process time applies to the product and processing conditions in the heat penetration test.
CALSoft offers users the ability to easily evaluate/plot the heat penetration data to generate heating factors and to calculate a thermal process using the Ball Formula method.
It is important to understand that the basic assumptions made in the Ball Method result from empirically defined terms in the method which allow for an “estimation” of both process time or sterilizing value. Unfortunately, these assumptions often overestimate process lethality and, although conservative, do not accurately define the actual lethality delivered in the process. The Ball Method utilizes heating and cooling factors to predict the internal product slowest heating zone temperature. The following assumptions are fixed within the method for your products:
BASIC ASSUMPTIONS:
- jc = 1.41 (hyperbolic cooling lag)
- fc = fh (slope of linear logarithmic cooling = slope of linear logarithmic heating)
- RT-Tw or m+g = 180°F (steam) or 130°F (water)
- 42% correction of come-up time in calculation of jh value
- No further product heating after cooling starts
- A constant retort temperature method only
These assumptions make Ball Method flexible but also very conservative, over-estimating the actual lethality delivered to the product (mostly occurring in cooling). In the case of conduction heating products, there is often as much as a 100% increase in resulting lethality than that targeted in the scheduled process. Sometimes this is unacceptable to product quality and the Ball Formula is not the most appropriate process calculation method.