Zonirushi ricecooker accuracy?

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mille162

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I bought the Zojirushi NP-NVC10 rice cooker last year and have used it only a handful of times (wanted a forget about it solution to making rice on the countertop at a catered event that didnt have adequate stove space). Besides it boiling over/venting steam that left a starchy residue I still can’t get off all its vents and underside, I noticed the clock was off. I set the clock to my cell phone (GPS turned on, sync’s with atomic clock every 10min so I know its accurate). This is 90 days elapsed time: ricemaker shows 7:37, cell phone shows 7:54. 17 minutes over 3 months is a pretty big discrepency!

so, this has me asking all types of questions, and will stores closed, can’t exactly walk back in with it to exchange it or ask questions.

1. Is the clock display just a stand-alone function, or is this a display of the bios clock?

2. Is the clock accuracy adjustable as a manual watch would be to sync it up to actual time

3. Is the clock inaccuracy affecting any other functionality? This is one of the highest rated and supposedly most accurate automatic rice machines available (yes I know, I can just use a pot of water on the stove, which is what I usually do and why this has almost no use).

4. Could the boiling over issue (venting thick bubbles of gooey starch) be a malfunction in the system as well, or is that normal/expected (directions and measurements were followed)
 

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Hey Mille,

I can[t speak to the clock inaccuracies but would think it's a non-issue. The only function of the clock (as far as I know) is to allow starting the rice maker at a particular time - once turned on it's just a clock.

The only time I've had issue with my 12 Qt Zo spitting out some liquid is when it was (probably) overfilled w water or had particularly starchy rice that had not been rinsed.

We've bought/sold from each other a couple times, I would be happy to drop my 12 in the mail to you so you could compare results. I use a 3 Qt Zo for daily.
 
How much are you cooking in it and are you washing the rice and are all the gaskets and internal parts properly seated?
 
daveb said:
Hey Mille,

I can[t speak to the clock inaccuracies but would think it's a non-issue. The only function of the clock (as far as I know) is to allow starting the rice maker at a particular time - once turned on it's just a clock.

The only time I've had issue with my 12 Qt Zo spitting out some liquid is when it was (probably) overfilled w water or had particularly starchy rice that had not been rinsed.

We've bought/sold from each other a couple times, I would be happy to drop my 12 in the mail to you so you could compare results. I use a 3 Qt Zo for daily.
Click to expand...

thanks! I might take you up on that offer in the near future!
If the click was connected to the overall bios, I thought the inaccuracy in time might be an indicator of another internal issue, that maybe the temp sensor was also off, or the timer was off?
 
Cooking 1/2 capacity, rice rinsed, everything is put together and fits fine. Afraid if the clock is off, then maybe the cooking sensors are also off
 
Was the cooker plugged in during most of the 3 months? Sometimes the internal clocks of gadgets have an accurate time base, like a digital watch, and sometimes they have an inaccurate time base and expect sync to the power line frequency, which is fairly accurate in the long term.

If you are worried about the accuracy of timing based on an error of 17 minutes in 3 months, remember that 3 months is about 60 x 24 x 30 x 3 = 126600 minutes. So that is a .013% error.

I have a Zojirushi rice cooker too and it only boils over when I make a quantity of rice close to the capacity, which I rarely do. It will vent steam though, and I had to move mine away from underneath a low cabinet to prevent it from damaging the wood.

I am really happy with the quality of the rice it makes, though.
 
Have never looked at my Zoji clock.
Always happy with the rice output and it’s a staple.
Capacity and rubber gasket fitting is the only thing that comes to mind. Occasionally if cooking a large quantity we get overflows at the vent but doesn’t impact rice quality.
You have any images of the before and after cook?
 
The clock on the Zojirushis is not terribly accurate; mine has fairly serious clock drift, too. I just ignore it: I don’t use my rice cooker to tell the time, just like I don’t use my wristwatch to cook rice.
 
Haven't had any boil-over problems with mine (the induction version), but I never use it at more than around half capacity, and I'm fanatical about rinsing rice before cooking. I'd suspect either over-filling or not rinsing enough for a boil-over.

I never use the clock function. I don't believe it affects cooking accuracy even if there's a little drift. I always start a digital timer on a lanyard at the same time as the rice, so I can do other things out of the kitchen and come pack to stir the rice when it's finished. The lanyard timer and rice cooker always finish at the same time, give or take a few seconds.
 
Maybe a dumb question, but are you using the measuring cup (that came with the cooker) for measuring the rice? Japanese cup = 200ml. Standard cup = 240ml. I have that same cooker, have used it at least 5 times a week for the past 10 years. It has never boiled over or otherwise misbehaved, and it makes fantastic rice. I wish it would reveal the remaining cooking time--it "knows" since it can have rice ready at a preset time. The clock is not very accurate on mine either, maybe a couple of minutes off every few months. I use the timer function often and it's accurate enough for that. My biggest complaint about it is the non stick coating wears out--I've replaced the bowl once and the replacement is now showing wear. The replacement bowls are really expensive so that's a big negative. I read somewhere long ago that these cookers have an internal battery that will run down and cause problems if you leave it disconnected from power for long periods. I don't know if that's true, but I mostly keep mine plugged in.
 
Michi said:
The clock on the Zojirushis is not terribly accurate; mine has fairly serious clock drift, too. I just ignore it: I don’t use my rice cooker to tell the time, just like I don’t use my wristwatch to cook rice.
Click to expand...
"We don't swim in your toilet, please don't pee in our pool".
 
Evan Estern said:
Maybe a dumb question, but are you using the measuring cup (that came with the cooker) for measuring the rice? Japanese cup = 200ml. Standard cup = 240ml. I have that same cooker, have used it at least 5 times a week for the past 10 years. It has never boiled over or otherwise misbehaved, and it makes fantastic rice. I wish it would reveal the remaining cooking time--it "knows" since it can have rice ready at a preset time. The clock is not very accurate on mine either, maybe a couple of minutes off every few months. I use the timer function often and it's accurate enough for that. My biggest complaint about it is the non stick coating wears out--I've replaced the bowl once and the replacement is now showing wear. The replacement bowls are really expensive so that's a big negative. I read somewhere long ago that these cookers have an internal battery that will run down and cause problems if you leave it disconnected from power for long periods. I don't know if that's true, but I mostly keep mine plugged in.
Click to expand...
Thanks for the comment on the difference between the Japanese cup and the Standard cup. Some of my first attempts were coming out too soggy. Will have to try again with that adjustment. I have been cooking whole grain blended rice with the Model NS-TSC10 and have been happy with the results, although at times have relied on "Kentucky Windage." It takes a long time to cook though (1hr 40 min). About to try the long grain wild rice.
 
Evan Estern said:
I read somewhere long ago that these cookers have an internal battery that will run down and cause problems if you leave it disconnected from power for long periods. I don't know if that's true, but I mostly keep mine plugged in.
Click to expand...

I have a NS-LAC05 model that we don't keep plugged in. The clock continues to work, so it definately has a battery for some reason...

I use the included plastic measuring cup and the measuring scale on the side of the insert bowl with good results for short grain Japanese rice.
 
Last edited:
mille162 said:
I bought the Zojirushi NP-NVC10 rice cooker last year and have used it only a handful of times (wanted a forget about it solution to making rice on the countertop at a catered event that didnt have adequate stove space). Besides it boiling over/venting steam that left a starchy residue I still can’t get off all its vents and underside, I noticed the clock was off. I set the clock to my cell phone (GPS turned on, sync’s with atomic clock every 10min so I know its accurate). This is 90 days elapsed time: ricemaker shows 7:37, cell phone shows 7:54. 17 minutes over 3 months is a pretty big discrepency!

so, this has me asking all types of questions, and will stores closed, can’t exactly walk back in with it to exchange it or ask questions.

1. Is the clock display just a stand-alone function, or is this a display of the bios clock?

2. Is the clock accuracy adjustable as a manual watch would be to sync it up to actual time

3. Is the clock inaccuracy affecting any other functionality? This is one of the highest rated and supposedly most accurate automatic rice machines available (yes I know, I can just use a pot of water on the stove, which is what I usually do and why this has almost no use).

4. Could the boiling over issue (venting thick bubbles of gooey starch) be a malfunction in the system as well, or is that normal/expected (directions and measurements were followed)
Click to expand...
Every timing mechanism, mechanical and quartz, has inaccuracies. They tend to drift. The most accurate time available is what is broadcast by the NIST station, WWV, down to the millisecond. Cell phone time queries Network Time Protocol, and is very accurate. You would have to sync up to one of these periodically to get accurate time. You probably don't need this level of accuracy.
 
The measuring cups that come with the machine are avail on Amazon as "accessories". Whole grain, black rice etc, work for me on the brown rice setting. For the more glutenous rice there's a different measuring cup.
 
I have the NS-LAC05 3 cup version, got it in 2014. The clock is also off by 43min, I keep it plugged in all the time and probably haven't changed the time for years. I never look at the clock on it. It keeps the time even when unplugged for short periods of time, so there must be a rechargeable battery or capacitor in it.

It has some kind of logic/sensor and adjust the cook time based on how much is put in. If you're putting in the correct rice/water ratio with the cup that comes with it (not standard US cup size), and not overfilling, maybe the sensors or controller is messed up?

I've only had it boil over or undercook when I overfilled it, past the highest capacity mark inside the pot. Sometimes when I cook at the full 3 cup capacity there are some bubbles that pop out of the vent on top, but there is no mess inside since the inner pot seals against the seals up on the underside of the lid insert.

I just checked and there is some pooling of moisture in the overflow reservoir, but I don't think it's a problem. I only regularly clean the removable pot and clean the reservoir and lid insert and wipe the inside maybe once a month or less. No mold or food poisoning yet for the past 6 years. Maybe because I use it so often, about 5 times a week, and it gets a 'steam cleaning' in those areas when the hot steam is venting.
 

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mille162 said:
thanks! I might take you up on that offer in the near future!
If the click was connected to the overall bios, I thought the inaccuracy in time might be an indicator of another internal issue, that maybe the temp sensor was also off, or the timer was off?
Click to expand...

FWIW, this thing is way too simple to have a BIOS or other centralized computing stuff. It's a handful of microcontrollers duct-taped together, including a clock of evidently dubious quality 😂

I'd only worry about the clock drift if it's so bad that it affects cooking time. It doesn't much matter if it thinks it's 9:45 when it's really 9:43, but it's pretty bad if your 22-minute cook stops after 18 minutes.
 
Evan Estern said:
Maybe a dumb question, but are you using the measuring cup (that came with the cooker) for measuring the rice? Japanese cup = 200ml. Standard cup = 240ml.
Click to expand...
This is correct, but the cup that comes with a Zojirushi is not a standard Japanese cup. Instead, it holds only 180 ml.
 
I can pretty much guarantee that the clock has nothing to do with the cooking process. I've had mine for at least 8-10 years or so, its hard to remember. Its an NP-HBC10 and spends most of its time unplugged. A year or 2 ago the internal battery died and I lost the clock and the setting I had for the start/stop chime. I never bothered to reset the clock or chime setting, and it still has the same dead battery in it. It makes perfect rice every time.

Knowing control loops and sensors, I would guess it's using a temperature probe to measure the rise/fall in temp based on how much power its putting to the heating element. Knowing how quickly it heats up and cools down you can infer how much water is in the bowl due to thermal conductivity. I could be completely wrong there, but I don't see any other sensors in there that would help control the cooker. It could also be measuring weight, but I would have to take it apart to check for a sensor to be sure.
 
Evan Estern said:
Maybe a dumb question, but are you using the measuring cup (that came with the cooker) for measuring the rice? Japanese cup = 200ml. Standard cup = 240ml. I have that same cooker, have used it at least 5 times a week for the past 10 years. It has never boiled over or otherwise misbehaved, and it makes fantastic rice. I wish it would reveal the remaining cooking time--it "knows" since it can have rice ready at a preset time. The clock is not very accurate on mine either, maybe a couple of minutes off every few months. I use the timer function often and it's accurate enough for that. My biggest complaint about it is the non stick coating wears out--I've replaced the bowl once and the replacement is now showing wear. The replacement bowls are really expensive so that's a big negative. I read somewhere long ago that these cookers have an internal battery that will run down and cause problems if you leave it disconnected from power for long periods. I don't know if that's true, but I mostly keep mine plugged in.
Click to expand...
Damn.
This.
Using the cup that comes with the machine has been second nature all my life so never thought to bring it up.
The cooking pot comes lined with markings for all the various water levels for different rice types measured by ’cup’
 
I got rid of my Japanese rice cooker not because of inaccuracies, which was no in priority, but because it uses potentially toxic PTFE Teflon nonstick pot. All of them are like that.

I went on a hunt for healthy ceramic pot based rice cooker instead. Turns out, it’s not available in the US. There’s a Japanese Model Tiger with ceramic pot cost $1500. I found & bought three China domestic model on Tao Bao, only $40 for each rice cooker, but $160 total in shipping, bit the bullet because I really need to get rid of all things Teflon.

I have one extra, it’s a 2-cup small
Model, anyone interested let’s me know. I’ll let one go for $50 + shipping in the US.

It’s 220v unit, needs a transformer to operated.(Amazon).
 
btbyrd said:
A standard Japanese cup (or "go") is 180ml.
Click to expand...
It seems that they have two cup sizes. 180 ml apparently is the original size (gō). Then they changed it to 200 ml later: "The Japanese later defined a "cup" as 200 mL." (Sadly, no reference is provided.)

I was always under the impression that it's 200 ml because that is quoted in some of my Japanese cookbooks. But I noticed at some point that the measuring cup for my Zojirushi rice cooker holds only 180 ml. Non-metric measurements are a mess everywhere…
 
Mine came with two cups. Always wash rice & use cups that came with the unit.

Cup lines on bowl are for smaller Japan size. Dont worry about PTFE think danger is over blown by people who preach it. I have some ceramic skillets they conduct heat well as with nonstick never go above medium heat.
 
Keith Sinclair said:
Dont worry about PTFE think danger is over blown by people who preach it. I have some ceramic skillets they conduct heat well as with nonstick never go above medium heat.
Click to expand...

Agreed. According to Zojirushi, their rice cookers shut off heat at 212 degrees F, which is far below the 500 degree danger point where PTFE starts to break down and out-gas.

I don't love the idea of PTFE -- I don't have any nonstick cookware because I just don't want to worry about staying at medium heat and not letting it get away. All our cookware is either stainless-lined copper, cast iron, or carbon steel. But at the low heat point of the Zojirushi I'm not too concerned about that coating.

The main concern, is that I've heard the coating eventually does start to break down just from age or wear, and the container needs to be replaced. So I'm careful to only use the plastic paddle the unit comes with, and I'm careful about washing it, not using abrasive scrubbers.
 
Unfortunately, one way or the other, TEFLON layer always get scratched. Both of my kids have used metal spoons despite repeated warnings. **** happens, nothing beats that it’s not there to begin with.

The second pint, the 500C is not a black & white transition, it doesn’t mean at 499c, there’s zero breakdown, it just mean that it’s acceptable amount break down.
However, what’s acceptable now may not be later as scientists constantly discover acceptable things giving people cancer, only that it’s 20 years too late.

Better safe than sorry.
 
I've been pretty careful with my cooker, but even so the PTFE lining eventually deteriorates. I'm on my second pot now and that's starting to go. I paid $85 for it 3-4 years ago. When I was shopping around for the best rice cooker available I tried really hard to find an all stainless steel or ceramic model, but every one I saw had some kind of nonstick.
 
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