Japan in July and August is not kind to dry foods. The relative humidity in most of the country sits between 70% and 85% for weeks at a time, and granola. Which is essentially a collection of porous, fat-coated oat clusters. Absorbs atmospheric moisture quickly once the bag is open. We get more questions about storage in summer than at any other time of year, so here is what we know from running the kitchen in Setagaya through eight summers.
Why granola goes soft in humidity ¶
The crunch in granola comes from the dehydration of the oat starch during roasting. When moisture re-enters the granola after opening, it is absorbed by the starch and the clusters soften. This process is faster at higher humidity and higher temperatures, which is why a bag left open on a kitchen counter in August will be noticeably softer within 48 hours. The fat coating from the sesame oil slows this process but does not stop it.
The best container for open granola ¶
An airtight glass jar with a rubber-sealed lid is the most effective storage container. Glass does not absorb odours and the rubber seal keeps humidity out more reliably than a clip-top bag or a loosely closed kraft bag. We recommend a 500 ml jar for a 250 g bag of granola, which gives enough headroom to shake the jar without the granola compacting. Avoid plastic containers if you can: some plastics absorb the sesame oil over time and transfer a faint plastic note back into the granola.
Should you refrigerate granola in summer? ¶
The refrigerator is a dry environment, which makes it tempting for summer storage. The problem is condensation: when you take a cold jar out of the fridge and open it in a warm, humid kitchen, moisture condenses on the cold granola immediately. If you do refrigerate, let the sealed jar come to room temperature before opening. About 20 minutes on the counter. Alternatively, keep the granola in a cool, dry cupboard away from the stove and kettle, which generate steam.
How long does open granola stay good in summer? ¶
In a properly sealed glass jar in a cool cupboard, open granola stays acceptably crunchy for about 14-18 days in summer conditions. After that, the texture softens noticeably even if the flavour is still good. If you find yourself with softened granola, spread it on a baking tray and put it in the oven at 150°C for 8 minutes. It will re-crisp as it cools. This works once; doing it repeatedly degrades the oat oils.
Our nitrogen-flushed bags and what they do ¶
The kraft bags we use are nitrogen-flushed before sealing, which displaces the oxygen and moisture inside the bag. This gives a 90-day best-before from the baking date on an unopened bag, even in summer. Once opened, the nitrogen is gone and normal storage rules apply. The baking date is printed on the back of every bag, not just the best-before date, so you know exactly how fresh the granola is when it arrives.
Summer storage is a small discipline that makes a real difference. A good jar, a cool cupboard, and the habit of closing the lid properly after each use will keep your granola in good condition through even the most humid August. If you have questions about a specific blend, get in touch with us at info@cedarvaultline.com.