From Flash Freezing to pH Testing: The Logistics of Safe Sushi

In its conventional usage, “sushi” refers to the popular Japanese delicacy in which cooked rice is formed with raw fish. Well-known variations include nigiri, maki, and hand rolls, made either manually using bamboo mats or mechanically using specialized tools.

Both of sushi's main components—raw fish and acidified rice—are highly perishable and prone to pathogens that can cause outbreaks of foodborne illness. Therefore, like other foods subject to HACCP protocols, the ingredients for sushi require strict attention to food safety and quality issues during all phases of the supply chain: transport, storage, preparation, holding, display, and sale.

In this post, we take a look at the logistics of safe sushi production, in particular best practices to ensure the safety and quality of both raw fish and acidified sushi rice.

The flow of raw fish: from boat to chopsticks

Sushi has become a standard dish nationwide. These days, you can find it not only at Japanese restaurants, but also at food courts in shopping centers, special deli counters at supermarkets, and even pre-packaged in cold display cases at the corner convenience store. Most often, these retail locations are miles from the ocean — which means the fish is not local.

Sophisticated diners know that the term "sushi-grade" fish indicates high quality. This label reassures consumers that it is safe to eat, as well as tasty. Consumer demand has pressured purveyors of sushi to move its fish ingredients across the supply chain as quickly as possible—the ideal being within 24 hours.

At sea, fish are flash-frozen on the boat within eight hours of being caught. For sushi-grade fish, extra care must be taken packing it for transport. The weight of regular ice bruises the flesh, while dry ice is too volatile to maintain a consistent temperature. Instead, best practice dictates that whole fish be carefully arranged with insulated ice packs.

Depending on the distance from catch to purveyor, the frozen fish then travels by airplane or truck to retailers nationwide. Specialty vendors such as International Marine Products Inc. operate hubs in coastal and landlocked cities and provide them with daily shipments.

FDA temperature and time regulations for handling raw fish

Currently, there are no mandatory federal guidelines to determine "sushi-grade.” Therefore, purveyors and chefs go to great lengths to ensure the freshest and safest fish for their customers in order to uphold their reputations.

What the FDA does address is proper handling procedures of fish meant for raw consumption in its Hazard Analysis Critical Control Point (HACCP) Fish and Fishery Products Hazards and Controls Guidance. This documentation provides information about the different temperature and time controls required for a variety of species of fish to be deemed safe.

FDA recommends the following general guidelines for “Parasite Destruction Guarantee” for fish after they are caught:

• Freezing and storing at an ambient temperature of -20°C or below for 7 days (total time).
• Freezing at an ambient temperature of -35°C or below until solid and storing at an ambient temperature of -20°C or below for 24 hours.
• Freezing at an ambient temperature of -35°C or below until solid and storing at an ambient temperature of -35°C or below for 15 hours.

Best practices for preparing raw fish

Once they have purchased raw fish from a vendor, chefs and kitchen staff should adhere to the following best practices.

Purchase, Transportation, and Receiving

• Buy high-quality fish from reliable suppliers.
• Ensure ingredients are not beyond their expiration date.
• Conduct a quality check to confirm that the fish has been frozen since capture.
• Transfer raw materials to an independent, hygienic environment.
  
  

Storage

• Store fish in designated freezer compartments to avoid cross-contamination.
• Store frozen fish at a temperature of -18°C or below.
• Closely monitor and log the freezer temperature using probe sensors.
• Adopt the "first-in, first-out" principle.
  
  

Preparation

• Defrost frozen raw fish in refrigerators at a temperature between 0°C and 4°C.
• Use designated sinks, knives, and chopping boards for handling raw fish.
• Prepare and serve to customers for consumption as soon as possible.
• Avoid re-freezing and re-defrosting.
  
  

HACCP temperature and time controls for sushi rice

Like raw fish, sushi rice is prone to outbreaks of foodborne illness if not handled and stored properly. The primary pathogens associated with cooked rice are Bacillus cereus and Staphylococcus aureus.  Bacillus cereus form spores that can survive normal cooking, while toxins from Staphylococcus aureus can contaminate rice improperly handled in unsanitary conditions. Although the FDA does not publish specific, mandatory guidelines for temperature and time control, each state typically publishes its own regulations based on proven HACCP protocols.

Temperature control for sushi chefs

The guideline for cooked sushi rice is the same as that for other perishable food products: refrigerate at or below 41°F.

Time control

Chefs choosing to keep and serve cooked sushi rice at room temperature must adhere to the following criteria:

• The rice container must be marked to indicate the time the rice was removed from a temperature-controlled environment.
• The rice must be served or discarded within 4 hours. 
• The rice may not be re-heated or refrigerated to be used after the 4-hour period.

Acidification: the safest preparation for sushi rice

Because temperature and time controls require meticulous attention to keep sushi rice safe, the standard preparation for most chefs is acidification. Quite simply, the cooked rice is combined with an acid—typically distilled white vinegar—along with sugar and salt. Acidified rice has the following benefits:

• Is easier to work with at room temperature. 
• Can be prepared less often and used for a longer period than non-acidified rice. 
• Can be maintained without temperature control. 
  
  

The importance of pH testing sushi rice

For safe consumption of acidified sushi rice, its pH measurement must be less than 4.4 at ambient temperature. This limit prevents the growth of pathogenic bacteria and the production of toxins. Testing can occur in two ways: use of a pH test strip or use of a pH probe meter.

pH strip test method

The following manual method is inexpensive but time-consuming and prone to error:

• Measure the acidity (pH) of the sushi rice within 30 minutes after acidification.
• Mix ¾ cup of distilled water and ¼ cup of sushi rice.
• Stir the mixture for 20 seconds.
• Dip test strip into the liquid portion of the mixture for the time period as directed by the manufacturer.
• Compare the color of test strip to color chart.
• Add more vinegar if the pH is more than 4.40. 

Probe meter method

A probe meter indicates the pH of sushi rice instantly on a digital display by measuring the concentration of hydrogen ions present. Probe meters provide more accurate and reliable results than test strips.

For example, the color indicator for test strips may be perceived differently by different testers than the actual result. Furthermore, probes can be inserted directly into the rice without having to make a slurry for testing, thereby avoiding errors in its preparation.

A pH probe meter is calibrated according to the manufacturer’s directions before first use and thereafter calibrated once a week to assure accuracy. The calibration is based on the readings from standard buffer solutions selected to provide specific pH readings.

Expand your SmartSense capabilities with the HALO2 Wireless pH Tester for sushi

The HALO2 Wireless pH Tester is a third-party device manufactured by Hanna Instruments for HACCP compliance for sushi rice. It is compatible with our SmartSense mobile app used for collecting data and analysis within the SmartSense platform.

Designed to bring simplicity to pH testing, the HALO2 Sushi pH Tester is engineered for use with sushi rice to ensure it meets the food-hygiene and Hazard Analysis Critical Control Point (HACCP) regulations.

• Specialized electrode for spot checking the pH of sushi .
• Water resistant protection.
• Easy integration into current data logging systems.

SmartSense is constantly working with innovative companies to integrate their products within the SmartSense platform. You can find more information about the HALO2 Wireless pH Tester for sushi and other third-party devices compatible with the SmartSense solution here.