What Are the Precautions for Raw Material Thawing in Aquatic Product Processing Workshops?

Raw material thawing in aquatic product processing workshops is a core control point in the pre-treatment link, which directly affects product texture, nutrient retention and food safety, and must strictly follow the principles of low-temperature time control, hygienic isolation and quality priority. Combined with the current aquatic product processing specifications and production operation requirements, the core precautions are as follows:

01

Pre-thawing Preparation and Raw Material Control

1. Thaw on demand and strictly prohibit repeated freezing and thawing

Accurately calculate the thawing amount according to the daily production plan, and prioritize the "small-batch, multi-batch" thawing mode; frozen raw materials shall not be refrozen after leaving the warehouse. Repeated freezing and thawing will damage the muscle cell structure, lead to massive loss of juice and soft and rotten taste, and significantly increase the risk of microbial reproduction.

1. Raw material sorting and pre-inspection

Before thawing, sort raw materials by variety, specification and batch, and eliminate raw materials with damaged packaging, thick frost and obvious signs of repeated freezing and thawing; raw materials shall comply with the hygienic standard of GB 2733 "Fresh and Frozen Animal Aquatic Products", and indicators such as volatile basic nitrogen and histamine shall be sampled for inspection when necessary.

1. Pre-disinfection of environment and tools and utensils

The thawing area is a general operation area for raw material treatment. Before each shift, tools and utensils such as thawing tanks, turnover baskets, operating tables and knives shall be cleaned and disinfected; temperature monitoring equipment shall be calibrated in advance to ensure accurate data.

02

Operation Key Points of Mainstream Thawing Methods

1. Low-temperature refrigerated thawing (priority for high-grade/raw food raw materials)

Applicable scenarios: raw aquatic products, high-grade fish fillets, raw materials with high quality requirements. It is the thawing method with the least juice loss and the highest safety.

Operation requirements: Place raw materials in a 0～4℃ cold storage in an elevated position to ensure air circulation and avoid raw materials being soaked in dripping juice; the thawing cycle of whole fish/large pieces of raw materials shall be controlled within 72 hours, and the core temperature shall be monitored throughout the process.

1. Air thawing (batch conventional raw materials)

Still air thawing: The ambient temperature shall not be higher than 18℃. Raw materials shall be placed in layers to avoid stacking, so as to prevent excessive local temperature rise. Pay attention to moisturizing during the process to avoid dry oxidation of the fish surface.

Flowing air thawing: The ambient temperature shall not be higher than 21℃. The thawing efficiency is improved by accelerating air circulation through fans, and the temperature of the fish body shall not be higher than 7℃ throughout the process.

1. Running water thawing (fast turnover scenarios)

Applicable scenarios: Small and medium-sized raw materials that need to be thawed in a short time, such as shrimp kernels, small trash fish and divided fish blocks.

Operation requirements: The water temperature shall be strictly controlled below 21℃, keep flowing throughout the process, and the total thawing time shall not exceed 4 hours; it is recommended to soak raw materials with sealed inner packaging to prevent water-soluble nutrient loss and secondary water pollution; raw materials of different varieties and batches shall be thawed in separate tanks, and mixed placement is strictly prohibited.

1. Microwave/high-frequency thawing (emergency rapid processing)

Applicable scenarios: Temporary material replenishment and small-batch urgent processing.

Operation requirements: Strictly match the raw material weight and power according to the equipment parameters to avoid local overheating and ripening; the surface temperature of raw materials after thawing shall not exceed 8℃, and they must be immediately put into the next process and shall not be stored at room temperature.

03

Core Temperature and Time Control (Safety Red Line)

1. Thawing end point control

Most processing scenarios do not require complete thawing. It is sufficient to reach a semi-thawed state with the core temperature of raw materials at 0～4℃, which not only facilitates subsequent division and shaping operations, but also minimizes juice loss; for raw materials requiring complete thawing, the maximum core temperature shall not exceed 5℃.

1. Upper limit of process temperature

The surface temperature of raw materials shall not exceed 7～8℃ throughout the thawing process, so as to prevent surface microorganisms from entering a large-scale reproduction state before the internal part is thawed.

1. Residence time limit

After thawing, immediately enter the cleaning and division processes, and the residence time at room temperature shall not exceed 30 minutes; temporary storage shall be in a 0～4℃ environment, and the total refrigerated storage time shall not exceed 24 hours.

04

Hygiene and Cross-contamination Prevention and Control

1. Area and tool isolation

The thawing area is physically separated from clean operation areas such as cooking and inner packaging areas; knives, cutting boards and containers are dedicated for raw material categories, with obvious signs, and disinfected at least once per shift to avoid cross-contamination between raw and cooked food and between different categories.

1. Outer packaging prevention and control

Removing the outer packaging of frozen raw materials shall be carried out in a special area to avoid dust and pollutants on the outer packaging contacting raw materials; raw materials with damaged inner packaging shall be evaluated separately, and those with serious pollution shall be discarded directly.

1. Wastewater and waste management

Wastewater generated by thawing shall be discharged in time, and the thawing tank shall be thoroughly cleaned and disinfected after each shift; waste packaging and unqualified raw materials shall be transported out of the workshop in time to avoid becoming microbial pollution sources.

05

Post-thawing Quality Control and Process Connection

1. Sensory inspection

After thawing, check the color, smell and tissue state batch by batch, and eliminate unqualified raw materials that are sticky, have peculiar smell and have soft and rotten meat; green-skinned and red-fleshed fish shall be inspected emphatically for signs of histamine spoilage.

1. Rapid circulation

After thawing, complete cleaning, impurity removal and division according to process requirements, and semi-finished products shall be transferred to the next process or temporarily stored at 0～4℃ as soon as possible to shorten the room temperature exposure time.

1. Disposal of remaining raw materials

Unprocessed thawed raw materials on the same day shall not be frozen again. They shall be sealed and refrigerated at 0～4℃, and must be processed within 24 hours. Those exceeding the time limit shall be treated as unqualified products.

06

Special Requirements for Special Raw Materials

Fish with high histamine incidence (mackerel, tuna, sardine and other green-skinned and red-fleshed fish): Thawing must be strictly temperature-controlled, the temperature throughout the process shall not exceed 5℃, and the thawing time shall be shortened as much as possible to prevent histidine from decomposing into histamine.

Raw aquatic product raw materials: Thawing shall be carried out in the quasi-clean operation area. Operators need to change clothes twice and disinfect hands, avoid contacting raw materials with bare hands throughout the process, and control the core temperature at 0～2℃ after thawing.

Small raw materials such as shellfish meat and shrimp kernels: Adopt short-time running water thawing, and stop when reaching the semi-thawed state, so as to avoid meat fragmentation and severe water outflow caused by excessive thawing.

In the production process, thawing records of each batch shall be well made, including raw material information, thawing start and end time, ambient temperature, raw material core temperature, operators, etc., to realize full-process traceability and meet the management requirements of aquatic product production license review.