Made for miso preparation. I hold miso-making workshops at my home in Ota-ku, Tokyo. However, after the miso is made, we've had many incidents where the bags burst due to the build-up of gas during fermentation in the warmer months. To prevent bursting, it's necessary to release the gas periodically. But, some people find it difficult to do this, especially when they are away on trips for extended periods. Also, when releasing the gas by opening the bag, it's easy to let air in, which can lead to mold growth and spoil the miso. I couldn't find any ready-made products with air release valves, or they were too expensive, so I had them custom-made by a manufacturer. I have a large stock, so I'd like to sell them on Mercari. Instant purchase is OK. You can prepare 2-2.5 kg of miso with this bag. The valve releases the carbon dioxide gas generated inside the bag. It has a check valve mechanism to prevent air from entering. Instructions for use will be provided in the transaction message after purchase (as it's a bit lengthy). The price is set per number of bags: 5 bags for 980 yen, 10 bags for 1700 yen, 20 bags for 3100 yen. If you wish to purchase a different quantity than listed, please leave a comment, and I will create a dedicated listing for you. *The cost of materials and shipping has increased, so I have revised the prices. This is the third price increase.* Thank you. ***I am continuously selling these. Price negotiations are not accepted.***