Biological and Food Engineering
Balance plus one rate
Biological and food engineering items usually reduce to a mass and energy balance plus a single rate relationship. Psychrometric problems (drying, storage ventilation, HVAC) require you to pin down dry-bulb, wet-bulb, dew point, humidity ratio, and enthalpy, and to recognize that wet-bulb equals dry-bulb at saturation. Drying problems separate the constant-rate period (surface moisture, controlled by air conditions) from the falling-rate period (internal diffusion, controlled by the product).
Thermal processing
Sterilization and pasteurization questions use D, z, and F. D is the time at a given temperature for a one-log (90%) reduction. z is the temperature change that produces a tenfold change in D. F is the equivalent time at a reference temperature. Use F = D (log N0 - log N) at the reference temperature; to convert, F_ref = F_T x 10^((T - T_ref)/z). Keep z in the same scale as the temperature you use; 10 C (18 F) is typical for C. botulinum spores.
Other core topics
Refrigeration load (product sensible and latent heat, respiration heat, transmission, infiltration), freezing-point depression with solute concentration, fermentation yield and stoichiometry, rheology (viscosity, non-Newtonian power law), and cleaning/sanitation (concentration, time, temperature).
Traps
Confusing D and z; using Fahrenheit in a formula built for Celsius; forgetting log reduction counts logs, not percent; ignoring product respiration heat in cold storage; treating wet-basis moisture as dry basis in a dryer energy balance.
Worked example
D at 121 C = 2.0 min, z = 10 C. For a 12-log reduction, F0 = 2.0 x 12 = 24 min. At 111 C, F = 24 x 10^(10/10) = 240 min. Halving the target to 6 logs halves both values: 12 min at 121 C.