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Posted on Jan 22, 2008 in Bento, Food Jar, Laptop Lunchbox, Sandwich Case, Thermal Lunch Jar, Tips, Tutorial or How-to | 49 comments

How to care for your bento gear

How to care for your bento gear


Cleaning under the rubber packing strip of a bento box lidBecause I like shortcuts and can get bento gear cheaply in San Francisco, I’m tough on my equipment and push the envelope when caring for it. I experiment with putting everything in the dishwasher for speed even when the care instructions say not to. As a result I’ve lost or damaged some equipment, but I’ve also figured out what can take a little more abuse than the manufacturer recommends.

Dishwashers are uncommon in Japan (I didn’t have one until my last year there), so a lot of bento boxes and accessories are made with hand washing in mind. If you have time and the inclination, hand washing all of your bento gear with regular dish soap will make it last the longest, but I wanted to put together bento care guidelines for people either looking for a shortcut or wanting to know what the Japanese care instructions say. At the end of this post I’ve included translations of common Japanese-language care instructions if you’re trying to decode what’s in your cupboard.

Do you have a clever bento care or cleaning tip? Share it with us in comments! (Click here for the full post…)


Hand Washing

For best results, use warm water, a mild detergent, and a soft sponge to keep everything in top condition. Avoid scrub brushes or abrasive scouring powders as these can mar the finish of your bento gear. If food is dried on, let it soak briefly before washing so as to avoid hard scrubbing that could leave marks. At the least, you’ll probably wind up hand washing most of your bento box lids and accessories (described below).


Plastics can warp and disfigure in the high heat of a dishwasher; one way around this is to turn off the heated drying cycle, put all plastics in the top rack, and avoid the high heat sterilizing setting if your dishwasher has one. Think of it as the gentle cycle for bento gear. Anything small that might fly around in the dishwasher and land on the heating element should go into a smaller lidded dishwasher basket, either one that comes with your dishwasher or one sold separately (often for washing children’s bottle or sippy cup pieces).


Only microwave containers that are designated as being microwave-safe, and avoid putting the lids into the microwave. The high heat of the food can warp flimsy plastic lids, and some of the wing/flap-type lids have metal in the hinges that shouldn’t go in the microwave. Avoid microwaving greasy or staining foods (tomato-based or curry-based, for example) that are in direct contact with plastic containers as this can cause pitting and staining. Be aware of food safety concerns about microwaving food in plastic containers and determine your own comfort level.



Prevention: Use the tips in my post on packing smelly foods to reduce food smells in your lunch. If possible, wash the container soon after eating (or at least throw away unwanted food bits and give it a quick rinse/wipe with a paper towel).

Cure: After washing, put the open containers (lids off) in direct sunlight for an afternoon to air them out (storing the containers with their lids off also helps odors dissipate). For stubborn odors, some recommend applying a paste of lemon juice and baking soda. Cascade’s Plastic Booster can be added to the dishwater (either dishwasher or handwashing) to help the detergent work on plastic, whitening and deodorizing plastics.


Prevention: Pack tomato-based or other staining foods (like curry) in Pyrex or non-reactive metal containers, dark-colored plastic containers (like dark blue or red), food cups (disposable, reusable hard plastic, or silicone), or line the container with a barrier like lettuce, plastic wrap or an antibacterial lunch sheet to cover. Avoid microwaving containers packed with greasy or tomato-based foods as this will cause the plastic to discolor (or worse, pit). (See my tips on microwaving.) If you’re not going to microwave staining food in its container, you can also spray the container with vegetable oil spray or wipe with cooking oil before packing, creating a barrier against stains (this does increase the calorie count and affect flavor, though). If possible, wash or wipe out the container soon after eating.

Cure: To lighten stains on clear or white containers, place in direct sunlight or soak in hot water with a little lemon juice or bleach (wash thoroughly afterwards if you use bleach). Cascade’s Plastic Booster is a highly regarded product that can be added to the dishwater (either dishwasher or handwashing) to help detergent work on plastic, both whitening and deodorizing stained plastics. (EDIT: LJ user dollykat also finds that adding one or two foaming denture cleaning tablets to a stained box filled with water gets out stubborn tomato stains.)

* * * * *


Bento Boxes

Cleaning under the rubber packing strip of a bento box lidPacking strip: To maintain a watertight seal on flap- or wing-type bento boxes, periodically remove and wash the packing strip (the white rubber gasket that fits inside a groove in the lid) to keep it clean and pliable. You don’t need to wash it every time you wash the bento box, but regularly. Clean the crevice with a little brush, either a soft-bristled toothbrush or a special cleaning brush (I got a set of two at either Daiso or Ichiban Kan for about US$1; Amazon sells similar bottle brushes here). Be sure to allow both packing strip and lid to dry completely before reassembling. Bento box manufacturers in Japan sell packing strips separately if yours should ever crack, but it’s better to care for the one that came with your box than to go through the rigamarole of trying to replace one from a company that may not ship internationally. If your box or lid ever breaks and you’re going to throw it out, hold onto the packing strip as it might fit another box down the line, and they’re hard to replace outside Japan (I’ve never seen them for sale in the U.S.). Soft narrow brushes for washing bento box lids

Bottoms: I’ve found that most plastic bento box bottoms are just fine in the top rack of the dishwasher as long as the heated drying cycle is turned off.

Lids: After ruining some of my bento box lids by putting them in the dishwasher, I now hand wash bento box lids with a soft sponge (not a scrub brush or scouring pad). Lids made of soft, flexible plastic can stain and warp in the heat of the dishwasher (beware of the delicate inner lids of the Urara boxes!). Lids made of hard plastic (like the flap/wing type) are tougher, but the lid decoration tends to wear off faster in the dishwasher than hand washing. (The Feel at Ease bento box seems to be particularly vulnerable.) Side dish containers with decals can develop bubbles under the decal in the dishwasher. The workhorses of my bento boxes are the Lock & Lock brand boxes, though, whose lids are dishwasher safe. In general, avoid putting bento box lids into the microwave, as the high heat can cause warping and many hinges contain metal.

Laptop Lunchbox

Laptop LunchboxHooray! The Laptop Lunchbox’s inner containers and their lids are dishwasher-safe (top rack), and the containers can be microwaved without their lids. Hold off on packing vinegar-based salad dressings in the little sauce container as people have experienced problems with the lid cracking because of vinegar (any updates?). The lids will wear better in the dishwasher without the heated dry cycle. If washing by hand, you may want to run a soft-bristled toothbrush along the groove of the lid to make sure everything gets clean. The utensils that come with the Laptop Lunchbox are not dishwasher safe, though — some report cracking at the handle with repeated trips through the dishwasher. Best to hand wash these. Some people have also reported problems with a sticky residue when using the dishwasher to wash containers that were sealed with Glad Press ‘N Seal, but not when hand washed. I haven’t been able to replicate this, but FYI.

Thermal Food Jars

Small Thermal Food Jar

Insulated bento set

Hole in the bottom of thermal food jar

To prevent odors from developing in the metal containers, store with the lid off or cracked open. Follow the manufacturer’s recommendations for washing; my Nissan Thermos thermal food jar is watertight and the care instructions give a thumbs up for the dishwasher, but the cheaper thermal food jar in my thermal bento set has a tiny hole in the bottom that fills up with water in the dishwasher and leaks out afterwards. I now hand wash that one food jar.

Thermal Lunch Jars like the Mr. Bento

Nissan Stainless Thermal Lunch ToteThe care instructions for thermal lunch jars generally call for hand washing, but I’ve found that the bowls themselves do fine in the upper rack of the dishwasher (no heated dry cycle). Hand wash the lids for longest life, although I have been known to put them through the dishwasher on occasion with no ill effects (no heated dry cycle).

Collapsible Sandwich Cases

Collapsible sandwich holder (exploded)Although I hand wash the lids to protect the lid decorations (see above on bento box lids), the bases of the collapsible sandwich cases are fine going through the dishwasher.

Wooden or Lacquerware Bento Boxes

I don’t use wooden or lacquerware bento boxes; Just Bento has some notes on their care here.

* * * * *


PicksDecorative picks for children's lunches

Wooden picks should be hand washed, but you can put plastic and bamboo food picks through the dishwasher (upper rack, no heated dry cycle) if you use a lidded dishwasher basket to keep the picks from flying around the dishwasher and landing on the heating element. Many plastic picks include a warning that the oils and terpenes in citrus peels (such as lemon) can damage the picks. Manufacturers of plastic picks generally recommend hand washing, and warn against the dishwasher, microwave, freezer and oven.

Sauce Bottles

Pre-filled sauce containers for speedy lunch packingPeople are often puzzled by how to wash the tiny sauce bottles with screw caps (like the soy sauce fish). Some people avoid the whole washing issue by dedicating each sauce container to holding only one kind of sauce, but I prefer to wash them out with the same method I use to fill them. Unscrew the top and dunk the little fish in hot, soapy water. Repeatedly squeeze the sauce bottle underwater, forcing soapy water in and out of the bottle. To rinse, repeat the process in clean hot water. This is most effective when you wash the sauce bottle soon after using it. For dried-on sauces, fill the sauce bottle with hot soapy water and let it soak for a while. Put the cap on and shake it up to agitate, then wash as normal until clean. To dry, I prop them upside down in the dish rack and let them air dry. (Variation: Flickr user Kate Ford uses an old Water Pik to blast her bento gear clean, getting water into all of the nooks and crannies.)

Reusable Hard Plastic Food Cups

Reusable plastic food cupsThese are more delicate than they look, and don’t do well in the freezer, microwave or dishwasher (let alone the oven). They won’t deform if washed in a lidded dishwasher basket in the top rack of the dishwasher (no heated drying cycle). But they often turn over during the wash cycle and fill with water, requiring a hand wash in the end. Save yourself a step and just wash them by hand with a soft sponge.

Reusable Silicone Baking Cups (used as food cups)

Silicone cupcake linersThese are pretty indestructible — throw them into the dishwasher, oven, freezer or microwave. You can even take them out of the freezer with an individual portion of food, and put it right into the microwave without issues. They don’t do well with direct heat, though, so avoid putting them right into a frying pan, toaster oven, or under the broiler. Refer to the manufacturer’s instructions if in doubt. If I’ve cooked something stubborn in these like eggs, I find that baked-on bits don’t fully come off in the dishwasher and I need to give them a little scrub to finish the job.

Condiment Cups (i.e. mayonnaise cups)

Condiment cups for bento lunches The surest way to get these clean is to hand wash them, especially if they have stickers on them (i.e. the Clickety Clack mayo cups). Condiment cups without stickers can be washed in a lidded dishwasher basket in the top rack of a dishwasher (no heated drying cycle), but they’ll often turn over in the dishwasher and not get fully clean, necessitating a hand wash anyway. Paper stickers come off in the dishwasher, and plastic stickers can develop bubbles underneath.

Disposable Plastic Food Dividers (“baran”, i.e. sushi grass)Small food dividers for bento lunches (

Yes, these are originally meant to be used once and thrown away. But you may be reluctant to toss them either for cost or environmental reasons. Because plastic food dividers are usually quite thin and delicate (especially sushi grass), these are best hand washed with a soft sponge and air dried. When I’ve put them through the dishwasher, they tend to stick up to the side of the dishwasher basket and not get fully clean.

Lunch Bags

Cars bento lunch bag for childWhen one of Bug’s unlined cloth ‘kinchaku’ lunch bags gets dirty, I just toss it into the laundry with everything else. For longer life, you can either hand wash these or turn them inside out and put in a mesh washing bag before tossing it into the washing machine. Kinchaku with decal patterns will thank you for drip drying, but I’m too lazy for this and toss them into the dryer as well. There’s been a bit of fading over time that probably could have been avoided with a regimen of hand washing and drip drying, but that’s too much work for me.

Insulated Lunch Bags

Insulated bento bag (large)It’s best to follow the manufacturer’s care instructions with these; generally they’re looking to be spot cleaned or wiped with a damp sponge. With the Laptop Lunchbox’s insulated carrying case, Flickr user traceyk73 writes here that she had luck hand washing it, then propping it open on a sweater rack in the dryer for 40 minutes on the air dry cycle.

Drink Containers with Reusable Straws

Narrow brushes for washing reusable strawsMany of my preschooler’s drink containers have built-in reusable straws that need to be washed between uses. Huge pain. Placing the straws horizontally in the dishwasher doesn’t let enough water inside to clean them sufficiently, and they drop right through the holes in my dishwasher’s utensil basket. I finally got a tiny round brush to use when hand washing Bug’s straws (US$1.50 at Daiso, Amazon sells similar bottle brushes here) to use when hand washing Bug’s straws. It’s a pain, but the straws definitely get clean and I can also use the tiny brushes to clean little holes in cup lids. (EDIT: Reader Polcamilla uses pipe cleaners from the craft store for this — good idea!)

* * * * *


Below are some common care instructions you may see on Japanese packaging for bento boxes or accessories. I knew there was a reason I held onto all of that packaging! (If you have trouble displaying these on your computer, try adjusting the “Character Encoding” setting in your browser’s View section to include Japanese.)

Don’t wash in dishwasher.

  • 食器洗い機、食器乾燥機は作用しないでください。
  • 自動食器洗浄機・食器乾燥機には使用しないでください。

Don’t put in the freezer.

  • 冷凍庫でのご作用はおやめください。
  • 冷凍庫では使用しないでください。

Don’t put in the microwave or freezer.

  • 電子レンジ及び冷凍庫では使用しないでください。

Don’t put in the microwave or toaster oven.

  • 電子レンジ・オーブン等でのご作用はおやめください。
  • 本体は電子レンジ、オーブン、グリル機能での使用はできません。

Don’t put in the microwave, oven or dishwasher.

  • 電子レンジ、オーブン、食器乾燥機、食器洗い乾燥機等で使用しないでください。

Don’t put in oven or place near direct heat (causes warping or melting).

  • 火のそばに置かないでください。 変形することがあります。
  • オーブントースターや直火では作用しないでください。
  • é«˜æ¸©ã«ãªã‚‹å ´æ‰€ã€ç‰¹ã«ç«ã®ãã°ã«ç½®ã‹ãªã„ã§ãã ã•ã„ã€‚ç†±ã«ã‚ˆã‚Šã€å¤‰å½¢ã™ã‚‹ã“ã¨ãŒã‚ã‚Šã¾ã™ã€‚
  • グリル、オーブン機能での使用は出来ません。
  • オーブン・グリルでの使用はできません。
  • ç›´æŽ¥ã€ç«ã«ã‹ã‘ãŸã‚Šã€ã‚ªãƒ¼ãƒ–ãƒ³ã‚°ãƒªãƒ«ç­‰ã§ã®åŠ ç†±ã¯ã§ãã¾ã›ã‚“ã€‚

Wash before first use.

  • ご使用前に洗剤等でよく洗ってください。

Don’t wash with a scrub brush or scouring powder as it’ll damage the surface.

  • タワシや磨き粉で磨くと、傷がつきます。
  • たわし、またはみがき粉でみがくとキズがつくことがあります。

Microwave cautions

  • 電子レンジ作用上の注意
  • 電子レンジ使用上の注意

Remove lid before putting in the microwave.

  • 電子レンジで使用の際はフタを外して使用してください。
  • é›»å­ãƒ¬ãƒ³ã‚¸ã§ä½¿ç”¨ã®éš›ã¯ãƒ•ã‚¿ã‚’å¿…ãšã¯ãšã—ã¦ãã ã•ã„ã€‚ãƒ•ã‚¿ã‚’ã—ãŸã¾ã¾åŠ ç†±ã™ã‚‹ã“ã¨ã¯ã§ãã¾ã›ã‚“ã€‚
  • 電子レンジでご使用の際は、上フタ及び内フタをはずしてください。(Remove both top and inner lids before microwaving.)

Avoid microwaving oily or greasy foods as they can overheat.

  • æ²¹è„‚åˆ†ã®å¤šã„é£Ÿå“ã‚’å…¥ã‚Œã¦é›»å­ãƒ¬ãƒ³ã‚¸ã‚„ã‚ªãƒ¼ãƒ–ãƒ³ã§ã”ä½¿ç”¨ã®å ´åˆã€è€ç†±æ¸©åº¦ä»¥ä¸Šã«ãªã‚Šã‚„ã™ã„ã®ã§é¿ã‘ã¦ãã ã•ã„ã€‚(also avoid the oven)
  • æ²¹åˆ†ã®å¤šã„é£Ÿå“ã®åŠ ç†±ã¯é¿ã‘ã¦ãã ã•ã„ã€‚
  • æ²¹åˆ†ã®å¤šã„é£Ÿå“ã®åŠ ç†±èª¿ç†ã¯ãŠã•ã‘ãã ã•ã„ã€‚
  • 電子レンジ対応ですが長時間の温めにより、油分の多い食材(唐揚げ)などは、本商品の耐熱温度以上になることがあります。長時間の温めはお止めください。(Don’t heat for long periods of time, especially with oily foods like fried chicken.)

Use the microwave only to warm foods in this, not to actually cook in it.

  • 電子レンジでご使用できるのは、温めるだけです。調理用に使うことはできません。

Refer to your microwave oven’s instruction manual for further cautions

  • その他の使用上の注意については電子レンジの説明書にしたがってください。

The oils and terpenes in citrus peels (such as lemon) can cause damage (to plastic food picks).

  • レモン等、柑きつ類に含まれるテルペン又は油脂によって変質することがあります。