1. Why Water Collects on Vegetables Sprinkled with Salt
When salt is sprinkled on vegetables, a strong salt solution forms on the outside of the vegetable cells. The membranes of these cells let water pass through but block most dissolved salt. As a result, water inside the cells is pulled out toward the salty exterior. This action is called osmotic pressure, and it causes the vegetable to become soft and release water [1].
If enough water leaves and the salt concentration is high, it becomes harder for microbes to cause spoilage. According to the Ministry of Agriculture, Forestry and Fisheries (MAFF), pickling for preservation usually requires a salt concentration of 15% or more to prevent microbial decay [2]. A concentration of 15% or more is quite salty.
It is important to note that 15% is a guideline for long-term salt storage. Light pickles and home-made rice bran pickles are not this salty. Salt removes water and reduces spoilage, which is easy to understand. However, pickles also have a sour taste that salt alone cannot explain.
2. How Lactic Acid Bacteria on Vegetables Build Flavor and Preservation
In the Kiso region of Nagano Prefecture, there is a pickle called "sunuki-zuke." It is made by fermenting lactic acid bacteria found on the stems and roots of red turnips, and its main feature is that it uses no salt [2]. Pickles where salt is not the main ingredient can still work well.
According to MAFF documents, during salting, lactic acid bacteria and other microbes attached to the vegetables increase in number, enhancing the fermented flavor [2]. A review of fermented pickles states that lactic acid bacteria are key microorganisms. They create sourness and flavor, and also improve preservation by producing antibacterial substances like lactic acid and bacteriocins [3].
Here, the answer to our main question appears. Salt pulls water from vegetables, and sufficient salt prevents decay through concentration. Then, lactic acid bacteria on the vegetables grow, developing sourness and flavor while also boosting preservation. Pickle-making is not a single process; both the work of salt and the work of lactic acid bacteria affect taste and shelf life.
However, how lactic acid bacteria grow changes depending on the pickling bed. For example, what kind of bed is a rice bran bed that you stir every day?
3. What a Rice Bran Bed (Nuka-Bed) Is Made Of and Why You Stir It Daily
A rice bran bed ("nuka-bed") is made by adding salt and water to rice bran, which comes from polishing brown rice into white rice, and letting it ferment. It is said that stirring it daily to introduce air is important, and a fermented nuka-bed contains more than 10 types of microbes, including lactic acid bacteria, butyric acid bacteria, and yeast [4].
The review on fermented pickles notes that in rice bran pickles, lactic acid bacteria become dominant as the bed matures [3]. Daily care is thought to support this change, but the sources do not describe the exact relationship between stirring frequency and bacterial growth.
Rice bran pickles spread widely from the Edo period onward, when polishing technology advanced and more people in cities ate white rice. Because making white rice produces large amounts of rice bran, pickling became a way to use this byproduct [4].
Rice bran was utilized as a pickling bed. In the world of pickles, not just the ingredients but also the bed plays a leading role.
4. How Pickling Beds of Salt, Rice Bran, Sake Lees, and Vinegar Change the Pickle
Sources list examples for each type of pickling bed. Salt pickles include Nozawana greens and plums. Rice bran pickles include takuan (yellow radish) and iburigakko (smoked daikon). Sake lees pickles ("kasu-zuke") involve vegetables salted first, then pickled in sake lees, such as Nara-zuke or wasabi pickles. Vinegar pickles include rakkyo (Chinese onion) and ginger [2].
This source divides pickles into two main groups: those made directly by microbes on the vegetables, and those using fermented products like koji, miso, soy sauce, sake lees, or rice bran [2].
Vinegar pickles are interesting. Acetic acid in vinegar has properties that inhibit microbial growth, so fermentation does not occur. This is a different preservation method from pickles where microbes work, like Nozawana greens [2].
Even within the same category of "pickles," some remove water with salt and borrow strength from bacteria, while others suppress bacterial activity with vinegar. All aim to make food last longer, but they use different tools. Which pickle has the oldest written record?
5. Winter Melon Pickled in Sake Lees on Wooden Tablets from the Nara Period
Wooden tablets were excavated from the ruins of Prince Nagaya's residence in Heijo-kyo, the capital during the Nara period. One tablet had "Kasutsu-mouri" written in ink, indicating that a sake lees pickle of winter melon (Mouri) was delivered. A serial article by the Agency for Cultural Affairs states this might be an ancestor of Nara-zuke, a famous specialty of Nara [5].
According to MAFF documents, the oldest recorded pickle is "salt-pickled uri (gourd)" mentioned on wooden tablets from the Nara period. The Heian-era text "Engi-shiki" lists vinegar, soy-sauce, and sake-lees pickles, suggesting that most modern pickles existed by this time [2].
However, the lees pickle in "Engi-shiki" is not necessarily the same as today's Nara-zuke. The phrase "might be an ancestor" is a suitable level of certainty.
There are explanations that vegetable skins were salt-pickled during the Jomon period. However, this is a traditional explanation; written records support pickling only from the Nara period onward [2].
The review on fermented pickles describes pickles as food with "at least 1400 years of history," citing the wooden tablets from Prince Nagaya's residence as evidence [3].
6. A Kitchen Experiment on Salt and Water Using a Cucumber
You can try this today. Slice a cucumber thinly (use a knife with an adult) and arrange it on a plate. Sprinkle a pinch of salt on one side only, wait about 10 minutes, and compare whether water appears.
Also look at what happens to the side without water. If you change the amount of salt, you can observe how the amount of water released changes [1].
If you want to read more, the MAFF page on local cuisine classifies pickles like salt, rice bran, lees, and vinegar pickles, and explains sunuki-zuke. Reading this while looking at ingredient lists on pickle bags at home can help you identify which type of bed each pickle uses [2].