Measuring pH during Soy Sauce Production

Measuring pH during Soy Sauce Production

Soy sauce as we know it today traces its origins back in eastern cultures to at least 535AD. Salty, sweet, aromatic, savoury, and floral all contribute to the umami, the flavour of the soy sauce. Soy sauce is the by-product of the fermentation of a mixture of soybeans, wheat, and salt. Traditional methods of producing soy sauce are broken up into three main steps: koji fermentation, moromi fermentation, and the refining process.

During koji fermentation, soybeans and wheat are fermented with bacteria. The soybeans are first soaked in water, drained, and then boiled. The wheat can be roasted separately, introduced raw, or boiled with the soybeans. The inclusion of wheat in conjunction with the soybeans helps create desired growth parameters for favourable moulds and bacteria. The mixture cools and mould is introduced and incubated at a controlled temperature. The mixture, called koji, is then allowed to ferment for a few days. This first stage of fermentation allows for the conversion of raw material into a complex array comprised of proteins, amino acids, nitrogen, sugars and enzyme activity.

During moromi fermentation, a salt brine is introduced and the soybeans and wheat are macerated into mash and allowed to ferment for at least several months. It is during this step that lactic acid bacteria are used and yeast is introduced to convert sugars to alcohol. As the different stages of fermentation progress the temperature of the mash will fluctuate, and the pH will acidify from approximately 7.0 to a pH of approximately 4.5. This change in pH is as a result of the production of lactic acid from fermentation; once the pH reaches a level of pH 4.5, fermentation is complete and the soy sauce is ready for the next stage.

The resulting mature mash, or moromi, is squeezed and the subsequent liquid is raw soy sauce. The final step in production is refining. Raw soy sauce is filtered, clarified, pasteurised, and clarified again before bottling.


A commercial condiment company decided to expand their product line to include soy sauce to cater to the growing market. The company communicated with Hanna Instruments that they needed an easy to use product that was readily mobile to monitor the temperature and pH in the fermenting vats of soy mash as well as on the finished product line. They were worried as many of the employees did not have a scientific background and had complained about other products not being intuitive to use.

Hanna Instruments suggested the HI2202 edge blu and HI10482 HALO Glass Body pH Electrode with Clogging Prevention System and Bluetooth® connection. The HALO family of electrodes is unique as they function via Bluetooth® connection with either the HI2202 edge blu or the Hanna Lab App on compatible devices. This capability allows the user to utilise a laboratory meter or a personal device to take easy portable readings of their samples. HALO electrodes are digital electrodes meaning the calibration data is stored in the electrode, not the meter. This allowed the customer to easily switch between the HI2202 edge blu and Hanna Lab App without having to recalibrate each time.

The HI2202 edge blu is a tablet style meter that is supplied with a benchtop or wall mount cradle, and internal rechargeable battery with 8-hour battery life. The customer was pleased with the flexibility to use the edge as a benchtop meter in the lab or portable meter on the production floor. The HI2202 features up to 5 point calibration, 0.001 resolution, and Hanna’s exclusive CAL Check feature which gave the customer confidence that their electrode was in good working condition every time they calibrated it.

The HI10482 is designed for testing in the food industry with a ground glass double junction and PTFE sleeve to prevent clogging issues that can arise with food applications. The customer appreciated the high flow rate and clog-proof junction design, as some of the condiments they were producing were extremely viscous. The general-purpose pH glass of the probe can be used in samples that range from 0°C to 80°C. This feature would lend itself well to the soy sauce making process as the temperature varies greatly from step to step. The HI10482 has a double junction reference design. This meant the electrode utilised a silver-free reference electrolyte, minimising the risk of silver leaching into the food products. The HI2202 edge blu and HI10482 provided an intuitive and comprehensive solution to the customer’s condiment testing needs.


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