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Posted on Aug 6, 2007 in Equipment, Parent Hacks, Tips | 24 comments

Box lunches: Hot or cold?

Box lunches: Hot or cold?


A question I’m often asked is if we eat our box lunches hot, cold, or at room temperature. I mean, I often pack fruit next to savory foods that could heat up nicely in the microwave, so what do I do? Nuke the fruit?!? Unpack our lunches and then replate after warming? What a pain.

The answer is that because Bug hasn’t started preschool yet, we usually have our lunches outside at a park, zoo or playgroups where there is no microwave. So we eat them at room temperature or chilled unless I’ve packed them in a thermal food jar or a thermal lunch jar such as the Mr. Bento . But there are a number of tricks to keep in mind when deciding how to pack…

Reusable ice blanket for packed lunches

For a room temperature lunch:

  • First off, read my post on packed lunch food safety so you don’t get sick. This is important. I don’t want anyone spooning yogurt into a bento box, carrying it around at room temperature, and then wondering why they feel ill afterwards. Be smart about what you pack to eat at room temperature, or be sure to carry it in an insulated lunch bag with an ice pack (edible or plain) to keep things cool.
  • Season food more aggressively than you would if you were going to eat it warm: add more spices and flavorings. This is an often-touted tip in Japanese bento lunch cookbooks as the secret to delicious room-temperature food, and spices often have antibacterial properties (see the food safety post).

If there’s a microwave where you eat:

  • First, be aware of recent health concerns about microwaving food in plastic, and microwave safely. You may want to line your container so that the food doesn’t come into direct contact with the container, repack/heat the food in a non-plastic container, or skip the microwave altogether. Figure out your comfort level and adjust accordingly.Fritatta lunch
  • Pack one microwaveable container solely with microwave-friendly food, and put cold foods in another. You can dedicate one tier of a two-tier bento box, use separate Tupperware containers, or use removable sub-containers. The Laptop Lunchbox (shown at right, click photo for lunch details) has easily removable sub-containers, as do some better quality bento boxes. Packing hot/cold foods separately means you won’t have to unpack and replate warmed food.
  • Oily or greasy foods can overheat in the microwave and cause pitting or discoloration to plastic food containers, so protect your lunch container by packing especially oily food in cupcake liners, on paper towels, or on an edible equivalent such as lettuce (yes, you may not want to eat lettuce after it’s been through the microwave, but your container will be undamaged and you’ll still have a environmentally friendly lunch).
  • Season the food to be warmed as you usually do — no need to spice especially strongly as you might for room temperature food.
  • In the portion of the lunch that’ll be microwaved, avoid aluminum food cups and any lunch accessories that cannot be microwaved.
  • When microwaving most Japanese bento boxes, do not microwave the lid (if all-plastic it may warp, if hinged it may contain metal).

If you’re using an all-metal lunch container and want a warm lunch:

  • Pack all food to be warmed in one tier of your metal lunch container, so that cool side dishes like fruit or dairy can be easily separated out in a separate tier. The Chinese stacking lunchbox or To-Go Ware food tin are examples of this sort of multiple-tier container. Indians have been using this kind of tiffin tin forever!
  • If you have access to a microwave, you can jury-rig a microwave steamer to warm your entire lunch in its covered metal container. Find a large microwave-safe container large enough to hold your lunch container, and fill it with a half inch or so of water. Heat the larger covered container in the microwave until boiling, remove, and put your covered metal container into the larger container. Wait for 10 minutes or so until warm, depending upon how much food you’ve packed and the dimensions of the containers. If that doesn’t do the trick, you may want to rewarm the water in the larger container, and stir up the food in the metal container.
  • If you have access to a stove and a couple of frying pans where you’ll be eating (but no oven), you can jury-rig a steamer to warm your entire boxed lunch. Put half an inch of water in a deep frying pan or wok, elevating the metal container if possible on a steaming rack or shallow dish, and cover with another frying pan. Steam gently on the stove until warm, stirring the food as necessary. If you have access to a deeper pot, you can use a regular lid instead of another pan.

(EDIT: I’ve fixed the bug that prevented readers from being able to comment on posts over the past couple of days — some comment code got scrambled up with the Feedburner form to subscribe to daily Lunch in a Box posts by e-mail. All good now, sorry for the inconvenience!)



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  1. Great tips.

  2. @1 from Jessica:
    Ah hooray, you’re able to post comments again! Thanks for bringing the problem to my attention in e-mail, Jessica.

  3. @ 2 Biggie,
    I settled for trying to make a small comment and it worked ;). So hooray indeed :).

  4. I found the ice blanket a few days ago, right where you said it would be in Target. I love it! Although, I accidentally made two packets pop because I cut too close to the fluid.

  5. Hey, I just found one of these at my local supermarket:
    (no affiliation, yada yada)
    So far I’ve used it two days in a row, and will be using it tomorrow. That little ice-shelf in it’s center, which acts as a shelf for holding the two little boxes, works really well to keep my food cool until lunch time. The box fits right in my vinyl, insulated lunchbag, too. I can fit enough food in it for lunch, and a snack in the late afternoon, too. So far I’m very happy with it. (We’ll see if I’m still satisfied at the end of the week.)

  6. @4 from Niphil:
    Great that you found it! (and US$2.50 is definitely the right price) Too bad about the mess, but happy safe eating…

  7. @5 from grapeshot:
    I have a couple of the Fit & Fresh containers — the salad one and the soup/salad combo. They’re a bit bulky, but I like the built-in ice pack. (The ice ring on the soup/salad combo is faulty, though, and breaks the first time people freeze it — myself included. Grrr.) I’d be interested in what you think of the lunch container at the end of the week, grapeshot; let us know!

  8. Thanks for this information. I have been wondering about whether you reheat food or eat it cold. Very useful tips. I’m glad I found your site before school starts so I have some time to find packing materials.

  9. @8 from Melissa:
    Perfect timing, then — cool. I really like those little thermal food jars; they give me a lot of flexibility for soups/stews/curries as well as warm rice, even. Like $15-17 at Target or Walmart.

  10. @5 from grapeshot:
    I also bought that container and find it quite nice. It’s a very good size and is pretty sturdy. I especially like the ice pack.

  11. I just wanted to know if you had any ideas on which container would be bestfor keeping “hot” sandwiches hot for a school lunch?

  12. @12 from Eileen: Gosh, what kind of sandwiches are we talking about? I can’t think of the ideal container offhand; for something like hot Sloppy Joes I’d pack the filling in a thermal food jar or thermal lunch jar (like the Zojirushi Mr. Bento) and make the sandwich just before eating.

  13. i have a cute lunch container my mom picked up somewhere (there is even a little slot on the inside for a cute fork and spoon that are ultra skinny and nestle together) but it does not say what kind of plastic it is, all it says is “made in china” it does not have the cup and fork symbol. any concerns of putting food in it? maybe just not certain foods? i’ve been doing crackers so far..

  14. Hi! I know this is an old post, but was hoping you’d see this comment. Do you have any experience microwaving onigiri after it’s already been wrapped in nori? Sometimes I send it to lunch for Hubby already made… then he puts it in the fridge at work. I tell him that microwaving it will soften the rice again, but what will it do to the nori?

  15. @14 from melissa: If you have concerns about it, you could always pick up a surface lead test kit from your nearby hardware store. They’re super-sensitive, though, picking up ANY presence of lead (not just unsafe levels). You could also try lining the box with a piece of lettuce or food wrap.

  16. @15 from Bitsy: You know, all of my Japanese bento & onigiri books say to just freeze the onigiri without nori, and wrap it with nori after you’ve microwaved the onigiri. Long story short, I haven’t actually experimented with freezing & nuking already-wrapped onigiri. If you wind up trying it out, I’d love to hear your feedback on results!

  17. Biggie I looked everywhere here for some of those mini icepacks that you use to no avail and didn’t want to pay a huge amount to ship them in. My dad came up with an equivalent and managed to get me a couple for free. They are a special type of icepack which stays cold for DAYS! Literally. I clocked one at 2 days and still cold. Amazing thing.

  18. @18 from Metanoia: Wow, those ice packs sound amazing!!! Do you have a product name and/or link you could share with us?

  19. @19 Biggie: They say “Dry Ice 2000″ on the pack, but I really have no idea where you can get them in a domestic sense.

  20. @20 from Metanoia: Hmm, a Google search on “Dry Ice 2000″ doesn’t turn up anything useful. Too bad.

  21. Look at this site. This type of ice pack is said to remain cool for days.

  22. @22 from Amy: Fascinating products! It took me a while to find their pricing (on their Products page, not on the Order page), but interesting nonetheless!

  23. Good advice and a nice post. I had no idea there is an issue with plastic containers and microwave ovens. Is it all plastic?

  24. How would you keep a chicken sandwich hot for a school lunch?