We learned from one of our customers that sushi rice has the potential to become a host for pathogens if not properly prepared. To protect against this, it is imperative that proper amounts of vinegar are added to maintain optimum acidity.
To ensure proper acidity levels are achieved, a pH meter should be used to test each batch of rice. A maximum pH reading of under 4.6 is generally considered safe. In many states, there are specific laws in place that state sushi rice pH MUST be between 4.1-4.6.
There are two different ways that you can measure the pH of sushi rice. Method one is to use a pH meter with a probe for measuring non-liquid items such as rice. We used the Sper Scientific Basic pH Meter (840087) in our experiment and a Spear Tipped pH probe (840049), which is designed especially for measuring non-liquid items. We also used Sper Scientific Large Display pH Pen (850050) and compared the methods.
The meter and probe is by far the easier of two methods in that you can simply insert the spear tipped probe into rice and get your reading. In order to use the pH pen you have to make a slurry (instructions below) in order to take your readings. When using the slurry method you need to ensure there is enough moisture in the rice for the electrode to be fully saturated. In either case, you should conduct a pH test within 30 minutes after acidification of cooked rice to accurately test your sushi rice.
To make a rice slurry you start by gathering a ¼ cup sample of cooked, acidified rice taken from various locations in the batch and add ¾ cup of distilled water in a clear cup. Blend the slurry for 20 seconds to create a thorough mix. Once you have created your slurry mix you insert the pH pen in the mixture and let it rest for few seconds before you take your reading.
In both cases, you should calibrate your meter and probe with both a pH4 and pH7 calibration solution prior to taking your readings to ensure the accuracy of your readings.
Sper Scientific offers several pH meters and pH pens that can be used to test the pH of your sushi rice. The pH meters can be purchased for as little at $77 and the spear tipped probe costs $83. The pH pens start at $37.