You might have learned that bento originated in Japan as a form of packed dried rice, but do you know that even in nowadays, most Japanese people still eat bento without reheating it?
Up till today, most Japanese bento makers still wake up at 4 or 5 am to cook for their loved ones or themselves, so that they can enjoy fresh and delicious bento at lunch time. As a result, most Japanese bentos don’t require reheating and can be served at room temperature.
However, it’s extremely difficult to follow this traditional bento preparation schedule. I for one am a lover of delicious bento, but I also love my beauty sleep. I deal with this dilemma by:
(1) Breaking up the time of mealprep and assembling bento
(2) Reheating bentos based on the type of dishes

Separating meal prep and assembly process brings more flexibility to my schedule. Usually I meal prep most of the ingredients and dishes in the weekend, so that during the weekdays, I can quickly bring together meals and bentos. Besides, depending on the type of food that I pack in bento box, I follow the corresponding timeline to reheat it. Generally, bentos can be categorized as: Cold, Warm, and Hot bento.
Cold Bento: No Reheating Required
For food such as salad, spring roll, and sushi, reheating is not required but since it usually contains raw ingredients, once it’s assembled, please store these food in a cool environment and finish them as soon as possible.
Cold Bentos are great for summer time or picnic for they are usually light and refreshing. Pack an ice gel pack with your cold bento and place them in a cooler bag to keep it fresh.

Sushi Sandwich bento is great for picnics or hiking

Braised pork bento is flavorful when it’s hot!
Hot Bento: Reheat Bento Right Before Eating
On the contrary, hot bentos are those food which you have to enjoy while it’s smoking hot, including curry, stews, and dishes with fatty meat or thick sauce.
Hot bento may seem inconvenient at the first sight, but it brings out most flavor and fragrance of the dishes. It’s works best as a splendid meal when you need to quickly relax yourself from work or school.
Still, please store hot bento at low temperature before reheating for the sake of food safety.
Warm Bento: Reheat 3-4 Hours Before Eating
Warm bento could be a compromise solution for some hot bento when there’s no way for you to access microwave during lunch time. Classic warm bentos contains fried or grilled dishes, and other dishes with less gravy.
Most Japanese bento can be categorized as warm bento for the light usage of oil and umami-based seasonings.

Grilled salmon and sweet egg roll are the most popular bento dish in Japan