1. Why a Famous Onigiri Shop Presses Rice Balls Only Gently
The owner of a shop with long lines of customers says that when making onigiri, you should press gently and lightly, about 3 times [1]. This might surprise those who think you need to pack the rice tightly. However, another article suggests aiming for 7 presses, keeping the touch "fluffy and gentle" [3]. That same article notes that shaping them into perfect triangles can make them too hard; slightly round and imperfect shapes are said to taste better. While 3 and 7 presses differ, both sources agree on not packing them tightly. These are guidelines based on experience, not fixed rules with a single correct number.
2. How Light Squeezing and Cooling Rice Leave Air Between the Grains
The shop owner also recommends cooling freshly cooked rice for about 5 minutes. When the rice cools to around 60 degrees Celsius, the grains shrink slightly, creating spaces for air, which results in a crumbly texture [1]. A rice expert explains a similar idea: if you shape the rice gently while it is hot, air gets between the grains. This keeps the rice from packing too tightly even after it cools, helping it hold its shape [2]. In other words, light squeezing means leaving air between the grains. If you squeeze hard, those spaces collapse, and the texture becomes hard. Note that these are explanations from shops and experts, not results from studies that directly measured the link between squeezing force and texture.
3. How Much Salt Should Go Into Onigiri?
There is a range in the amount of salt used. The shop owner uses about one finger’s worth of salt for immediate eating, and two fingers’ worth for bento boxes [1]. Another article suggests about one-third of a teaspoon of coarse salt per onigiri [3]. The rice expert says touching the belly of 2 to 3 fingers lightly to the rice is enough [2]. Since finger counts and teaspoons are different units, it is hard to compare the numbers directly, but it is clear that amounts vary by shop. The sources do not say why more salt is used for bento boxes. This raises a question: does salt actually prevent spoilage? We will check this in the next section.
4. Why Bacteria Can Still Grow in Salted Rice Balls
Salt inhibits bacterial growth because it dissolves in water, reducing the water available for microbes to use. This explanation comes from Hiroshima Prefecture’s food hygiene documents, using fish paste products as an example [4]. It does not state that the salt on onigiri is enough to stop bacteria. According to the Food Safety Commission, Staphylococcus aureus can multiply even at salt concentrations of 16–18%. If other conditions are right, it can produce toxins (enterotoxins) at 10% [5]. Rice balls are listed as a cause of staphylococcal food poisoning in Japan [5]. The shop guidelines give amounts in fingers or teaspoons, not concentrations, so they cannot be directly compared with 10% or 16%. Even so, salt alone cannot be relied on to keep onigiri from spoiling.
Note: What the fact sheet shows is that some bacteria can grow even in high-salt environments, so salt alone should not be trusted to keep onigiri safe.
5. How Using Plastic Wrap Changed Bacteria Counts in Onigiri
The Ministry of Health, Labour and Welfare advises using plastic wrap to shape onigiri in its disaster meal guidance [6]. Data from a Kyoto City experiment (2015) supports this. At 30°C, they compared bacterial colony counts (clumps of bacteria seen in culture) in onigiri made in different ways. With unwashed hands, counts were 194.5 after 2 hours, 507 after 4 hours, and over 500 after 6 hours. With washed hands, counts were 38.5, 114.5, and over 500. Onigiri made with plastic wrap had a colony count of 0 at all measured times. Gloves showed 0 to 7.5 [7]. At 6 hours, counts were over 500 for both washed and unwashed hands. Note that this experiment did not test the effect of salt. The colony counts are measurements from cultures and do not directly predict the likelihood of actual food poisoning.
6. A Yayoi-Period Rice Clump and Heian-Period Tonjiki
In November 1987, cone-shaped carbonized rice clumps that fit in a palm were excavated from the Suginotani Chanobatake site in Nakanoto, Ishikawa Prefecture (Yayoi period). An article suggests these were steamed rice onigiri [8]. It was speculated that they were wrapped in bamboo leaves, which may have had sterilizing effects, and heated, making them similar to chimaki (rice dumplings). Viewing carbonized rice as onigiri is an estimate, and the sources do not mention whether salt was used. According to the Ministry of Agriculture, Forestry and Fisheries, "tonjiki" mentioned in The Tale of Genji (Heian period) were rice balls made from steamed glutinous rice, served to lower-ranking people at noble estates [9]. These sources do not show whether ancient people used salt for preservation. However, they show that people have been shaping cooked rice by hand for a very long time.
7. How to Compare Squeezing Methods for Onigiri at Home
You can compare squeezing methods at home. Wash your hands well and use plastic wrap. Divide the same amount of rice into three portions and use the same amount of salt. Make three onigiri: one squeezed hard 5 times, one lightly 3 times, and one with medium force. Eat them immediately and compare how they break apart in your mouth. Keeping the rice temperature the same makes the difference in squeezing clearer. This method lets you check if expert advice matches your taste. Results may vary by person, which is normal. Eat the onigiri you make right away.
Where to read more: When looking for information, shop explanations are in [1], [2], [3]. The relationship between salt and bacteria is in Hiroshima Prefecture’s Q&A [4] and the Food Safety Commission’s fact sheet [5]. Hygiene in shaping is covered in Kyoto City’s documents [7].