Pages Menu
Categories Menu

Posted on Mar 27, 2007 in Equipment, Parent Hacks, Tips, Tutorial or How-to | 31 comments

Food safety for packed lunches (old and new wisdom)

Food safety for packed lunches (old and new wisdom)

A major concern when packing lunch is making sure the food won’t spoil by the time it’s eaten. I’ve been doing some research on the different methods Japanese and Americans recommend for safe packed food, to reconcile traditional wisdom with new methods and research on foods with antibacterial properties. There are many different methods, I’ve described them in detail below with sources. These are only guidelines for food safety; please make your own decisions about what you’re comfortable packing and eating (I am not a food safety authority).

An outline of methods to ensure your packed lunch won’t spoil (details behind the cut):

  1. Incorporate food and products with antibacterial properties
  2. Keep it clean: Don’t introduce bacteria into the lunch when packing
  3. Keep hot foods hot and cold foods cold, using thermal jars and cold packs
  4. Pack less perishable foods, especially in the summer
    • Extra precautions for hot weather
    • Handy foods for hot weather
    • How to make dishes less perishable

1. Incorporate food and products with antibacterial properties

  • Foods

Japanese bento cookbooks often suggest packing foods with antibacterial properties in lunches in order to keep food from spoiling. Suggested foods include umeboshi (pickled plum), wasabi, ginger, karashi, salt, shiso, parsley and vinegar (i.e. making sushi rice, or putting an umeboshi or a tablespoon or two of rice vinegar in the cooking water when making rice). Some books recommend wiping the inside of the bento box with a slice of ginger before packing.New USDA- and NSF-funded research on foods with antibacterial properties has yielded a number of additions that are interesting when packing non-Japanese food for lunch. The strongest antibacterial foods (killing all bacteria) are evidently garlic, onion, allspice and oregano. The second strongest (killing up to 80% of bacteria) include thyme, cinnamon, tarragon, cumin (and lemongrass). The third strongest (killing up to 75% of bacteria) are capsicums, including chilies and hot peppers. The fourth strongest (killing 25% of bacteria) include white and black pepper, ginger, anise seed, celery seed, and lemon or lime juice. Honey has antibacterial properties, and the dodecenal compound in cilantro/coriander (both fresh leaves and seeds) is evidently one of the stronger antibacterials as well. (see sources 1 – 3 below)

  • Products

There are a number of bento products in Japan that have been treated with an antibacterial coating (i.e. flavorless compounds extracted from wasabi, etc.), designed to help stave off microbial growth in packed lunches. These include aluminum food cups for cooking, plastic sheets that you place on the surface of your packed food, and food dividers (“baran”) that look like sushi grass. These must be touching the surface of the food to be effective. I bought the products below at local Japanese dollar stores and markets in San Francisco; click the photos for larger views and details. EDIT: Not all food dividers and food cups are antibacterial; they must have the Japanese characters that mean “antibacterial” on them (click the product photos below for a larger view with the appropriate characters pointed out in a note on the photo).

Antibacterial food dividers and bento sheets:
Antibacterial lunch dividers and bento sheets Antibacterial bento sheet in action

Antibacterial cups:
Antibacterial food cups

Keep it Clean: Don’t introduce bacteria into the lunch when packing

Make sure your hands, food prep area, utensils and lunch containers are clean. When possible, use utensils (chopsticks, spoon, tongs, plastic wrap) to place, mold and arrange unwrapped food in your lunch container. If you’re using a bento box with a rubber packing strip around the lid, be sure to periodically remove, wash and thoroughly dry the packing seal (and the groove in the lid). This will keep your box clean and ensure that the packing strip does not crack, which would leave you without a watertight seal.

3. Avoid the temperature danger zone with perishable foods

  • The danger zone for bacteria growth is between 40 to 140º F (4 to 60º C, or room temperature). An extremely effective way to keep food safe until you eat it is to minimize the time food spends in this temperature zone (ideally less than three hours). The USDA’s food safety page has a number of useful guidelines.
  • Keep hot foods hot by using a pre-heated insulated thermos or food jar for liquids like curries, soups, stews, etc. To pre-heat, fill the thermos with hot water, let it stand for a minute or two, empty the thermos, and fill with hot food (close it quickly!). You can get little kid-sized 300ml food jars at stores like Target or Walmart, bigger food jars, or even large thermal lunch jars with multiple containers inside (like the Mr. Bento or Ms. Bento) from
  • Keep cold perishable foods cold by storing your lunch in a refrigerator (if available) or using insulated lunch bags or containers with cold gel packs. Western versions include insulated lunchboxes, the Laptop Lunchbox, Fit N Fresh containers; Japanese versions include insulated bento bags and picnic sets, bento boxes with a gel pack integrated into the lid, and insulated bento kits (with a thermal jar for the lid, two lidded side containers and an insulated carrying bag that you can put a gel pack into to carry hot and cold items at the same time). Thermal lunch jars can also be pre-chilled with ice water and used to pack chilled lunches. Click on the photos below for a larger view.
  • Insulated Urara lunch bag Lock & Lock insulated picnic set (exploded view) Chilled bento box with built-in gel pack Insulated bento set

4. Pack less perishable foods,
especially in the summer. Rice becomes hard and unappetizing when refrigerated at low temperatures, so many Japanese forego refrigeration and cold packs for their rice-based bentos, choosing instead to incorporate antibacterial foods, pack foods that are less likely to spoil, and make their food less perishable through traditional cooking/packing methods.

A. Extra precautions for hot weather

  • Japanese bento cookbooks instruct you to make sure all food in a bento has been thoroughly heated through to the middle, so in hot weather scramble eggs until they are dry. Avoid raw or rare meat, poultry, fish or eggs. Avoid raw fillings for onigiri (make sure tarako is grilled). Heat (then cool) even processed meats like sausages or hot dogs before packing to kill any bacteria that may have been introduced after processing.
  • Avoid dairy products such as yogurt (especially when spooned out of a larger container).
  • Avoid moist, liquidy foods.
  • Avoid regular tofu as it sheds water into the bento and spoils easily.
  • Avoid raw vegetables except cherry tomatoes.
  • Avoid cut fruit as it spoils easily; pack whole fruit like a banana instead.
  • Exercise caution with cooked rice, potatoes, grains and legumes (spice heavily, mix with antibacterial foods, dry thoroughly).

B. Handy foods that survive summer heat

  • Cherry tomatoes
  • Rice that has been mixed with pickled vegetables, chopped umeboshi, or other foods with antibacterial properties
  • Whole fruit
  • Canned fruit that has been frozen in single-serving freezer containers (pack frozen to act as a cool pack)
  • One-bite jellies that have been frozen (pack frozen to act as a cool pack)
  • Juice boxes or bottled water that have been frozen (pack frozen to act as a cool pack)

C. How to make dishes less perishable

  • With moist, liquidy foods, first dry before packing (drain in a small colander or on paper towels) and pack in a paper food cup to contain any excess moisture.
  • Spice foods more heavily than usual.
  • If you’re cooking or heating foods right before packing them in a bento, be sure to cool them first before packing. Once you’ve packed the bento, allow the whole bento to cool further with its lid off to avoid condensation on the inside of the box. This also makes the box easier to open at lunchtime (an important point for preschoolers!).

1) 1998 Cornell study on antibacterial spices:
2) Cilantro article:
3) CookWise, Shirley O. Corriher, 1997.
4) The New Professional Chef, Culinary Institute of America
5) USDA lunch food safety guidelines:
6) USDA Freezing/Refrigerating time chart:
7) Aijo Tappuri! Obento, Shufu no Tomo, 2007.
8) Obento Daijiten, Index Magazine, 2005.


Share in top social networks!


Post a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

  1. This is just the post I’ve been waiting for!

    As always, you’ve taught me something. I really appreciate this handy guide, since my bento boxes will arrive this week.

    The antibacterial food section is easily the most interesting thing I’ve heard in a while (so far as food goes), and I can’t wait to try implementing them into my rice and lunches.

    Thanks a ton!

  2. I was actually going to post a question regarding this on bentolunch…thanks :D

  3. Glad you got something out of it! I found the antibacterial food info to be fascinating — if you think about it, it starts to explain the foodways of different cultures (spicier foods in hotter climates).

  4. Guess we’re on the same wavelength!

  5. My pleasure. Good for me to research as well, as I don’t want to make Bug sick (but sometimes keeping lunch cold until we’re ready to eat it isn’t feasible).

  6. When you say “regular tofu”, what do you mean? As in, straight out of the pack? I have some extra-firm tofu that we had for shabu-shabu; I put the leftovers in the broth to cook through, then packed it in the fridge in tupperware for bentô later, is that okay, do you think?

    I love the idea of freezing canned fruit, I use a lot of it for lunches and the idea of using it as a cooling pack is awesome.

  7. This is seriously like a grad school research paper or even a thesis! Thanks! One question – where can I get cool packs here? I used to re-use the ones I got from cake shops (they will give you mini-cool packs so cream won’t be melt while you take the box home) when I was in Tokyo.

  8. Thanks for the great info. I love that you add your “sources”. My daughters lunch had condensation on the lid today…and zero on the antibacterial foods. Are obentos meant to be eaten at room temp or cool? I’ve only added an icepack to her lunchbox when she has yogurt or cheese in it. Now I’ll be more careful. I wonder if that’s why they add salt to onigiri? So fascinating! I’m sure people thought more about this before refrigeration was available! –julie

  9. Wow, thank you so much, amazing!

  10. I meant not the agedofu, fried tofu or dry tofu skins. Some of my Japanese bento cookbooks warn against regular tofu (including extra-firm) because it sheds water into the bento and spoils easily. I’d say it depends how you pack it: does it get its own little container so moisture won’t get all over, say, your rice and other items in the box? Are you going to keep it cool until you eat it (or are you going to eat it within three hours of packing it)? If so, go for it.

  11. My pleasure!

  12. Thanks! I’m not a food safety expert, so I thought people would like to see where I got the info (I didn’t just pull it out of my ear). If there was condensation on the lid, that would probably be because you packed food while it was still warm and closed the lid on it before it cooled totally. Happens to me sometimes too. Japanese bento cookbooks would advise against that, especially for preschoolers, as it makes the lid hard to open in addition to the food safety issue.

    Traditionally bentos are eaten at room temperature, but there’s a new trend in Japan towards better food safety (insulated bento bags/kits, antibacterial products, more focus on antibacterial foods, etc.). Salt in the onigiri is, in fact, a way to keep the rice from spoiling — I found that very interesting!

  13. I had a feeling that’s what you meant, just checking. ;)

    Yes, it would be packed separately, or rather with the rest of the shabu shabu veggies in their own water-proof pack. The bentô is for my other half, she prefers to keep hers refrigerated at work, so I guess there’s not a problem?

    Appreciate the advice, by the way!

  14. Great Bento tips!

    I wonder, where are the good japanese dollar stores in San Francisco? I live in the Bay Area and I’ll be visiting the city this weekend. Any favorites, or stores that are easy to find and park at?


  15. Sounds like a smart way to pack tofu to me!

  16. Mostly I reuse ones that I get from other packages, but I know that Target has some cute ones for kids (SpongeBob Squarepants, etc.) and ugly/plain ones for adults. If anyone in the Bay Area knows of a good source (especially for small ones), chime in!

  17. Awesome, I love that you took the time to post this, it was really helpful! I love the idea of a rice-’lid’, now that I got my thermal bento it’s almost my favourite one, because I think warm food is so comforting.

  18. That is very informative. Thanks!

  19. I’m so glad this is getting read; sometimes I worry when I see photos of bento lunches with spoonfuls of yogurt in them (are they being refrigerated?). I do like the little thermal bento, but the little regular boxes are also nice when I’m carrying multiple lunches (me and Bug) as they’re smaller. I’m happy to have the option.

  20. I’ve been thinking those novelty reusable ice cubes would be good for bento (I live in Miami, everything gets hot), but they’re not as easy to find as I thought.

    The plain cubes, the ones that look like miniature baggies, however, are easily obtained and could serve for portable refrigeration if there’s no frozen items in one’s meal that day.

  21. Out here in San Francisco, I tend to see them in the summer at stores like Target, but I would have thought they’d be much more common in Miami. Good luck, and good tip, sff_corgi!

  22. Hmm, interesting work-around, quiet! I agree that I wouldn’t trust it next to food or for a child, but it’s still interesting.

  23. Yes, and they also put up Christmas decorations a fortnight before Halloween.

    Hmm, first aid items. Good idea. Not decorative, alas, but a good idea.

  24. …!

    Oooo… you’re good.

  25. Good tips on the first aid section for cold packs, and wrapping your lunch to insulate it. Japanese often do this with “lunch cloths” or furoshiki. The traditional bento-wrapping style is illustrated here as “Otsukai Tsutsumi”: (this how-to chart was produced by Japan’s Ministry of the Environment as part of an effort to reduce disposable bag waste).

  26. Thanks so much!
    I made it only to Ichiban Kan this time. Maybe I’ll get to Daiso next time, but I got TONS of stuff and so did my boyfriend!

    I got a new bento with an insulated container, an onigiri/musubi mold, 2 egg molds, little flying pig sauce containers, a bunch of nori and a couple elastic bento bands to hold it all together.
    great tips!

  27. Just a hint, I find those cute ice cubes at my local ross. I saw them in fish shapes, and flamingo shapes!
    I dunno if you have a ross out there, it’s a lot like marshalls and other department discount stores.

  28. [kicks LJ's Schwartz in the tuchus for database errors]

    Try, try again. Sorry.

    Oh, we definitely have Ross down here, for quite a few years now. And Marshalls, and I think there’s even a Burlington Coat Factory but only at Sawgrass Mills (coat stores do tyres??). Thanks for the tip!

    A work friend said the dollar section at Target, the display always right by the mail entrance, also has reusable cubes often. I haven’t made time to stop by and check yet, though.

    I guess they’re just too cheap an item to show up on-line…?

  29. SCORE! I’ve noticed that Ichiban Kan is really increasing their bento-related inventory lately, and not with just the same old stuff. I wonder if this is how they’re responding to the presence of Daiso nearby… Hey, the consumer wins in this battle, right?