By Jim Shimabukuro (assisted by Copilot)
Editor
Introduction: After baking whole wheat bread loaves for the last two years, I found weevils in my two flour containers. I store flour in these air-tight containers as soon as I get home from the market, so they were more than likely already in the flour. I threw out the infested flour and cleaned the containers. I was surprised to learn that, for storage, baking flour at low temperatures is an effective solution. -js
Weevils typically enter a home inside store‑bought flour because eggs are often present long before you open the bag, and warm, humid environments like Hawaiʻi accelerate their life cycle. Once inside a sealed container, the insects can mature unnoticed until the population becomes visible. Freezing and heat treatment are both effective because extreme temperatures disrupt all life stages, from eggs to adults.
Freezing flour for at least seventy‑two hours at 0°F is widely recommended to ensure that eggs, larvae, and adults are killed¹, and some sources note that three to seven days is also effective². Heat treatment works as well; baking flour at low temperatures such as 120°F for about an hour is cited as sufficient to kill both eggs and live weevils³. These methods are safe for the flour and do not affect its baking performance.
Preventing reinfestation requires attention to storage practices. Weevils thrive in dry goods and can spread from one product to another, so airtight, hard‑shelled containers made of glass, metal, or strong plastic are essential³. Even with good containers, newly purchased flour may already contain eggs, which is why freezing it immediately after purchase for several days is a reliable preventive step³.
Sifting flour can help remove visible insects, but it does not eliminate eggs or larvae, so it should be considered a supplemental measure rather than a primary control method. Discarding infested flour in sealed bags and thoroughly washing containers with hot, soapy water helps break the cycle and prevents surviving insects from migrating to new food sources.
Humidity plays a role in how quickly infestations develop, but the core issue is that eggs are often present before you bring the flour home. Freezing or heat‑treating new flour, storing it in airtight containers, and periodically checking for signs of pests—such as clumping, off smells, or tiny beetles—are the most reliable long‑term strategies.
Some people also place bay leaves in storage containers, though evidence for their effectiveness is anecdotal. The most dependable methods remain temperature treatment and proper storage.
References
- How long to keep flour in freezer to kill bugs for food safety —
https://theorganizedpantry.com/how-long-to-keep-flour-in-freezer-to-kill-bugs/(theorganizedpantry.com in Bing) - Does Freezing Kill Weevils in Flour, Rice, Beans, and Pasta? —
https://www.foodwine.com/freezing-kill-weevils(foodwine.com in Bing) - How To Keep Flour From Getting Weevils —
https://blog.entomologist.net/how-to-keep-flour-from-getting-weevils(blog.entomologist.net in Bing)
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