Trawling BQF Horse Mackerel

Trawling inevitably causes scale loss, bruising (ecchymosis), and pressure damage to the fish due to crowding and net abrasion. BQF (Block Quick Frozen) technology freezes many fish together into a solid block, which locks the fish in place as a uniform mass. For canneries, this solid block can be fed directly into a band saw to produce uniform portions without any thawing. The processing steps (heading, gutting, canning) completely hide the visual defects caused by trawling, such as scale loss or belly discoloration. In contrast, individual quick freezing (IQF) would present each trawled fish individually to the canning line, making the visible damage more apparent and potentially leading to more product downgrading during sorting.

Given the inherent damage from trawling, buyers should specify a Catch Damage Index (CDI) or an equivalent defect‑tolerance table in their contracts. For example, the CDI used in fisheries research scores damage categories (ecchymosis, gear marks, pressure injuries) from 0 (undamaged) to 3 (severe). For a trawling BQF product destined for canning or fishmeal, buyers can accept a CDI sum score ≤4 per fish, with no individual category score exceeding 2. This objective system replaces vague terms like "good quality" and gives both parties a clear, numeric reference for acceptance or rejection. This is especially critical for BQF blocks because the interior fish cannot be inspected without thawing the entire block, but the CDI can be applied to a thawed core sample drawn from the block center.

A practical non‑destructive method is the ice crystal sound test. Tap the frozen block gently with a hard plastic mallet. A solid, high‑pitched ringing sound indicates that the block has remained consistently frozen. A dull, thudding sound suggests that large ice crystals have formed due to partial thawing and refreezing, which softens the internal structure. Additionally, inspect the block surface: small, fine ice crystals are normal; large, jagged, or cloudy ice patches indicate temperature abuse. If abnormal sounds or surface ice are detected, reject the block or require further destructive sampling. Some importers also use a handheld infrared thermometer to scan the block surface; temperature variation of more than 3°C across the surface suggests uneven thawing. These quick checks help buyers reject compromised blocks before costly laboratory analysis.