I know, I know, it's cereus

November 2, 2015 1:19 PM

Is there somehow less of a problem with Bacillus cereus in Japanese rice? I often see remarks like this one about not refrigerating onigiri, and about leaving rice in the rice cooker for hours if not days and continuing to eat it. The worst food poisoning I have ever had was from B. cereus, so I am hypersensitive to rice preparation and storage.

Reheating will not help, since the spores survive cooking. Vinegar would not be enough, either. Do people regularly get sick from treating rice this way?

posted by fiercecupcake to Food & Drink (17 answers total)

According to the report:

The optimum temperature for growth in boiled rice was between 30° and 37° C. and growth also occurred during storage at 15° and 43° C.

The report also states that it's Chinese restaurants (that is, restaurants that prepare and serve "Chinese food" in North America), so it's reasonable to expect that the kitchen temperature in the restaurant is going to be around 30 degrees. It wouldn't be unusual if it was that warm in the kitchen.

We never refrigerate Japanese rice. We cook it in the rice cooker, and it stays in the rice cooker overnight until the next day when it is used for breakfast or lunch.

You don't want to refrigerate Japanese rice because it dries out in the fridge and will not taste good.

On the other hand, rice is seldom left out overnight in the rice cooker in the summer time, when the interior ambient temperature of our house is 30 degrees Celsius in high summer.

While we have never had food poisoning, the rice will quickly ferment and taste sour.

At other times of the year when the ambient temperature is around 20 degrees inside, we leave the rice out overnight in the rice cooker.

But with two growing boys the rice rarely lasts for more than 12 hours :)
posted by Nevin at 2:04 PM on November 2, 2015

Response by poster: Wow, that still seems shocking to me; just because optimum is between 30 and 37, it still grows at 15 and 43!

Maybe I am not understanding when you say you leave it in the rice cooker. Is the rice cooker still on and holding at a hot temperature?

Don't be led astray by the "Chinese restaurants" bit; all food safety classes I've taken in the US stress rice cooking, cooling, and storing very specifically, since B. cereus is present in even properly cooked rice.
posted by fiercecupcake at 2:08 PM on November 2, 2015

"Fancy" Japanese rice cookers, like the Zojirushi brand rice cookers, have a "Keep Warm" function that automatically switches on after the rice is finished cooking. I'm having a bit of trouble finding out what the exact temperature of this setting is, but this forum has a user who measured this setting in their Sanyo rice cooker and found it to be 137 F (58 C) (search for "temperature"). I would bet that a large proportion of Japanese families/individuals who talk about leaving their rice in a rice cooker for hours on end are utilizing this Keep Warm function, especially because it's automatic.

Personally, I have a Sanyo rice cooker with this exact function and I have no problems eating the rice after several hours on Keep Warm, from a health perspective. The manual says that the rice is safe up to 12 hours from cooking. However, I do tend to avoid eating Keep Warm rice after it's been at that setting for more than 5 or 6 hours because I find that the texture and flavor tend to suffer.
posted by andrewesque at 2:12 PM on November 2, 2015 [3 favorites]

I read through the forum thread a bit more (serves me right for posting without reading it through!) and later on, someone mentions the Keep Warm temperature is 158 F (70 C), and the poster who found a 137 F (58 C) measurement of cold water in the "Keep Warm" setting after two hours found that it rose to 161 F (72 C) overnight. Given that cooked rice is going to be cooling down from 212 F, not starting from room-temperature or cold water, the Keep Warm function is going to be sufficient to maintain the rice at a temperature above 145 F (63 C), which your attached link says is what's necessary to prevent B. cereus growth.

(and having had bad food poisoning/GI illnesses myself I sympathize with you! Although my Chinese-American parents leave rice on the countertop in Los Angeles overnight with no ill effects, I personally in my own kitchen always refrigerate rice.)
posted by andrewesque at 2:25 PM on November 2, 2015 [1 favorite]

Maybe I am not understanding when you say you leave it in the rice cooker. Is the rice cooker still on and holding at a hot temperature?

No, we never leave it on. That wastes electricity for one thing. "Cold" rice is reheated in the microwave.
posted by Nevin at 2:32 PM on November 2, 2015

I am not sure exactly what you're looking for in this question, whether it's advice on whether or not to specifically seek out rice sourced from Japan, or a specific set of (possibly) rice-related food preparation tips, or what. Whichever it is though, the NIH page is actually pretty clear: you should keep the cooked rice above 63C or quickly cool it below 15C (i.e., put it in the fridge, DON'T just leave it cool on the counter). Anecdotally this is what we do in my house, with the high temperature being maintained by the rice cooker's "warm" setting after cooking for up to ~3 hours if we are still eating, and after that sticking it in the fridge in a sealed container, minor texture and flavor changes be damned. Again anecdotally, we've never gotten food poisoning from rice, but of course there's never a guarantee.
posted by Joey Buttafoucault at 2:53 PM on November 2, 2015

Response by poster: To clarify, I'm wondering why people don't get sick all the time from leaving rice out for hours and hours in a rice cooker, or apparently DAYS unrefrigerated in that onigiri comment.

andrewesque, that is VERY helpful to know; I've never had a rice cooker with a Keep Warm function. Sounds like that keeps it out of the danger zone.
posted by fiercecupcake at 2:56 PM on November 2, 2015

That's weird. In twenty years living in and being connected to Japan I've never had food poisoning from rice, and I've never heard of anyone having food poisoning from rice. I wonder if Japanese rice has a protein that prevents this from occurring.

I can't speak for long grain or Thai rice which is typically used in Chinese food though, since we never ever touch that kind of rice if we can help it.
posted by Nevin at 2:58 PM on November 2, 2015

or apparently DAYS unrefrigerated in that onigiri comment.

That seemed rather odd. The onigiri, if left out overnight will taste pretty "pasa pasa" come morning. It would be inedible after 24 hours in that it would be totally pasa pasa and dry.

The benefit of keeping rice overnight in an unheated rice cooker on the counter is that it is sealed and keeps the relative humidity just right.
posted by Nevin at 3:00 PM on November 2, 2015

My take on the onigiri comment (as someone who has been making and reading a lot about onigiri lately) is that by "a day or two" they mean, like, made the night before and then at room temp in a lunch box all morning. Which would be about the same amount of time you'd have a sandwich at room temperature in the same context.

I can't think of a context where onigiri sitting out at room temperature for 48 hours would be even vaguely appetizing. Ew.
posted by Sara C. at 3:49 PM on November 2, 2015 [1 favorite]

A few risk-reducing factors:

1. "B. cereus spores can be resistant to heat and radiation, but heating at 100°C for 5 minutes results in cellular damage to the membranes and ribosomes"...
2. I would think rice cookers are designed to do the above.
3. Regular pot method of rice cooking starts with getting a hard boil for a few minutes.
4. Even if you don't manage to kill the spores, they still have to multiply up to the infectious dose to cause illness.
5. Rice held at the wrong temperature starts to smell like an old sponge. Fresh rice is fairly cheap.
posted by zennie at 4:12 PM on November 2, 2015

Isn't Japanese rice, or at least sushi-style rice, cooked with vinegar? Or prepared with it post-cooking? Perhaps this would delay the onset of rice plague?
posted by turbid dahlia at 4:34 PM on November 2, 2015

Epidemiologist chiming in. I want to narrow in on this comment:

...all food safety classes I've taken in the US stress rice cooking, cooling, and storing very specifically, since B. cereus is present in even properly cooked rice.

Clearly I'm not saying this as an official representative of my day job. That said, food safety courses are oriented toward overestimating risk. Makes sense, right? Err on the side of safety if you're feeding the masses.

B. cereus-related food poisoning is pretty rare if you're in the U.S., at least instances in which the magnitude is severe enough to seek medical diagnosis and treatment. It's best to practice expert food hygiene in commercial settings because the economy of scale is working against you: even relatively rare events will happen in settings that involve the preparation of a very large number of servings. In terms of people making foods at home, especially traditional foods in which the routine of preparation is tightly controlled and consistently performed (including hygienic preparation and storage), anecdotal evidence is much less likely to reveal its ugly head.

Many people, perhaps most people, do not observe CDC/FDA-sanctioned levels of food preparation safety in the home for all dishes. If you're capable of being as diligent as CDC/FDA advise--which is very, very diligent--then by all means keep doing so.
posted by late afternoon dreaming hotel at 5:59 PM on November 2, 2015 [5 favorites]

Okay, I figured it out. I asked my wife.

Traditionally***, Japanese cooked rice would have been stored in a wooden container (a nosebitsu). I don't know what variety of wood it would have been, but the wood would have antimicrobial properties. For example, there is a variety of mochi that is wrapped in cherry leaves in spring; the cherry leaves have antimicrobial properties.

A contemporary rice cooker, besides being sealed and therefore airtight when storing rice overnight is also apparently treated with some sort of antimicrobial film that probably contains silver.

Regular old white rice like we had for dinner tonight is not cooked with vinegar, by the way.

***BTW, it would take the Japanese to be defeated in World War II before white rice would become a staple food. Before the war due to low agricultural productivity and severe economic disparity, most people would only eat white rice once or twice a year if they were lucky. The rest of the year they would subsist on millet or perhaps buckwheat.
posted by Nevin at 7:07 PM on November 2, 2015 [2 favorites]

My daughter-in-law is Hawaiian, and keeps rice in the cooker. She believes that storing cooked rice in the fridge makes it too dry. Hawaii has medium humidity and even temps. Here in Maine, in the warm, humid, summer, rice stored out of the fridge molds fast.
posted by theora55 at 6:47 AM on November 3, 2015

Need to pop back in to debunk the myth that wood containers have some mechanism to disinfect contaminated food. They do not. At all. Wood doesn't generally have antimicrobial properties in a conventional sense. Storing foods in wooden containers is not the answer here.
posted by late afternoon dreaming hotel at 8:51 AM on November 4, 2015 [2 favorites]

It's very possible that "traditionally" sometimes people got food poisoning from rice and simply didn't connect the two things or didn't think food poisoning was a problem worth worrying about. Especially if rice was a luxury food item not consumed regularly by ordinary people.

There's a long history of wealthy people suffering for their rich diets, and the occasional bout of B. cereus related sickness might have been part and parcel of that for wealthy people in pre-industrial Japan.
posted by Sara C. at 9:58 AM on November 4, 2015