SOP: Conversion of Process Time According to Can Size

GIFSQ — Global Institute for Food Safety & Quality

Principle

If the heating rate fₕ of a product in one can size is known, the heating rate in other can sizes is calculated using conduction factors (for conduction-heating products) or convection factors (for convection-heating products) tabulated for the standard can sizes. The j value is assumed invariable with change in can size.

Materials required

• Table 25-22 of the book (conduction factors for different can sizes)
• Table 25-23 of the book (convection factors)
• Table 25-24 of the book (jar/can factors for glass jars)
• Known fₕ of the product in one can size

Procedure — Conduction-heating products

The heating rate fₕ is a function of can size and shape and the thermal diffusivity of the product. Since the thermal diffusivity of a given product is constant:

  fₕ(A) = (can factor A) / (thermal diffusivity)
  fₕ(B) = (can factor B) / (thermal diffusivity)

Therefore:

  fₕ(B) = fₕ(A) × conduction factor (B/A)

↓

Read the conduction factor B/A from Table 25-22 and multiply by the known fₕ; in the book’s example, fₕ of can size 401 × 411 = 40 min and the conduction factor for 300 × 407 = 0.592, so fₕ(300 × 407) = 0.592 × 40 = 23.68 min

Procedure — Convection-heating products

In homogeneous products whose viscosities are not considerably different from that of water, the heating rate is proportional to the surface/volume ratio of the container, incorporated into the can factor of Schultz and Olson; read the convection factor from Table 25-23 and apply it in the same way as the conduction factor above

Procedure — Glass jars

fₕ(jar) = fₕ(can) × factor for jar/can, reading the jar/can factor from Table 25-24

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

Schultz, O.T. & F.C.W. Olson — cited in the book.