Unit Operations and Equipment
This section covers Unit Operations and Equipment: mass balance, heat transfer, size reduction, separation, mixing, freezing, retorting and packaging equipment used in fish processing. The exam tests whether you can choose equipment for a duty and check a process balance.
Core rules
- Start with a mass balance: input = product + by-product + waste + loss. A balance that does not close signals a measurement or yield error.
- Freezing equipment includes air-blast tunnel, plate freezer, spiral freezer, IQF freezer and contact freezer. Choose based on product shape, throughput and whether pieces must flow separately.
- Retorts may be vertical or horizontal, still or rotary. Rotary retorts improve heat transfer in viscous products.
- Packaging equipment includes vacuum, modified atmosphere and shrink film. Check seal integrity and gas mix.
Worked example
A filleting line receives 500 kg fish. Fillet 55 percent, skin 8 percent, bone 12 percent, viscera 10 percent, trim 5 percent and loss 10 percent sum to 100 percent. Expected fillet is 275 kg. If actual fillet is 250 kg, the 25 kg gap must be explained by extra trim, over-trimming or weighing error. Reasoning: a mass balance turns a vague yield complaint into a measurable loss.
Traps
- Confusing machine capacity with usable throughput after changeovers.
- Ignoring glaze or drip loss in net weight.
- Overfilling a retort basket and blocking steam flow.
- Using one freezer type for all products.
- Recording input weight before washing but product weight after draining without noting the change.