Our short-term miso varieties (Chickpea, Mellow White, and Sweet White) are fermented using temperature control at 80 degrees F, while the long-term varieties (Brown Rice, Country Barley, and Traditional Red) are fermented in wooden vessels at room temperature for a minimum of 4 seasons. Each recipe has its own ideal fermentation time. Once that time is reached, miso should be refrigerated to halt further fermentation. In a nutshell, refrigeration helps to create a consistent product, rather than delay spoilage. We found that it takes around 3 days in warmer weather or around 5 days in cooler weather for the miso to “wake up” and start fermenting again, which is why we feel confident shipping miso unrefrigerated. Being exposed for a short period of time to warm temperatures has no ill effect on our product and only in very rare cases has caused a slight increase in fermenting the product further. We recommend refrigeration upon receipt to further extend the shelf life of our miso and ensure no increase in fermentation. Some of our miso flavors are fermented for 1 year or more, so transit time (even in warm months) is not an issue.