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Both my mother and grandmother, both now long passed away, would be horrified if when soaking beans, pulses, barley, lentils or rice etc. overnight for a soup or stew, the soaking liquid was used in the dish itself. My guess is that in their eyes, this action would reduce the amount of scum that floats to the surface during the cooking process, which to my knowledge, appears to be perfectly harmless protein which can be stirred back in.

Looking at similar questions, even the edge case of kidney or black beans, the liquid seems perfectly OK to use, provided it is cooked for the relevant period of time afterwards.

Is there ever a case when one should dispose of the soaking liquid rather than use it as additional flavouring to a stock (which is then cooked for a sufficient period)? Also, if that is not the case, should the pulses be stored in the refrigerator overnight as the liquid will have been stored well outside the safe temperature limits?

Greybeard
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    You don't soak rice, you wash it. The Indian fermented rice pancake known as a Dosa is an interesting example of these concepts. – Neil Meyer Aug 30 '21 at 19:33
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    Greybeard: I just noticed that your question includes rice and barley. The method of soaking both of these, and the ways of handling soaking water, are *completely* different from beans. I suggest that you omit these from your question; all of the answers below only concern beans, regardless. – FuzzyChef Aug 30 '21 at 20:35
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    @NeilMeyer You can absolutely soak rice, and some kinds of (black) rice *should* be soaked. – Konrad Rudolph Aug 31 '21 at 09:03
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    @NeilMeyer, the basmati rice I frequently use says it should be soaked for 30 minutes on the bag. – Greybeard Aug 31 '21 at 10:33
  • @FuzzyChef, which can be safely retained though? I'm thinking here of an overnight soak, I didn't realise there was different methods involved (other than possibly length of time). – Greybeard Aug 31 '21 at 10:37
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    Greybeard: if you want to ask about rice & barley, make it a separate question. – FuzzyChef Aug 31 '21 at 18:16
  • @NeilMeyer uruchimai (Japanese short grain rice) is soaked for at least 30 minutes too – Juliana Karasawa Souza Sep 01 '21 at 07:24

7 Answers7

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That water may contain all sorts of fungicides, dust, contaminants, rodent feces, insects, and so on. The process of production of beans is far from sterile. If you wash the beans thoroughly before soaking, you may avoid it, but a common kitchen practice is to just dump dry beans into water, maybe rinse once to get rid of the worst of the possible contaminants, then soak, stir a bit to detach whatever might have been stuck, and drain, and you have nice clean and well hydrated beans.

SF.
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    I add bicarbonate to my soaking liquid, and this should be removed before cooking. [It does](https://juniperpublishers.com/nfsij/pdf/NFSIJ.MS.ID.555765.pdf) [make a difference](https://onlinelibrary.wiley.com/doi/10.1002/1521-3803(20001001)44:5%3C339::AID-FOOD339%3E3.0.CO;2-T) – Juliana Karasawa Souza Aug 30 '21 at 09:17
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    @JulianaKarasawaSouza the paper says sodium bicarbonate negatively affected the flavor though. – SF. Aug 30 '21 at 18:56
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    @SF. You rinse the beans thoroughly when you remove it from the soda water. It just breaks down the hull of the beans – Neil Meyer Aug 30 '21 at 19:30
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    Most of the contaminations you list will actually be rendered harmless from cooking. By contrast, heavy metal contamination (especially [arsenic](https://www.bbc.co.uk/news/health-38910848)) in rice is somewhat common in many parts of the world (including, depending on the country of origin, Europe), and cooking doesn’t do anything about it. – Konrad Rudolph Aug 31 '21 at 09:04
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    @KonradRudolph Maybe harmless, but still disgusting. – SF. Aug 31 '21 at 10:25
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The other reason to discard the soaking water is (theoretically) limiting flatulence.

According to The Bean Institute and other sources:

Soaking overnight and then discarding the soaking water leaches out sugars in beans that are responsible for gas production.

Scientific evidence supporting this is weak and contradictory. However, it hasn't been disproven, and many cooks and nutritionists believe that a long soak followed by discarding the water reduces bean-generated flatulence. For this reason, the common practice is to soak for 8-12 hours, discard the water, and rinse off the beans.

FuzzyChef
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    I have always soaked my beans but it still produces spectacular flatulence. Something which is as high in fiber is just always gonna get your stomach moving. – Neil Meyer Aug 30 '21 at 19:27
  • That would also make a great deal of sense as M & G suffered from digestive problems and I can see the practice being looked upon as a possible solution. – Greybeard Aug 31 '21 at 10:46
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Maybe the women in your family would shocked because they had the practice of soaking beans in bicarbonate of soda. That is going to give up some unpleasant taste if you cook them in that liquid. Lentils typically need no soaking and you can cook them right out of the pack.

The problem with beans and lentils is that you cannot add salt or any acid during the cooking process. All the flavorings have to be added at the very end after the beans / lentils are thoroughly cooked. If you don't do that you get hard and cooked beans, which goes down about as easy as eating car tyres.

I have found beans and lentils to be a neutral tasting vegetable protein. It is the sauce and the spices that you make with it that makes it tremendous, I never really thought it had much of its own taste. The soaking of beans is a way to break down the fibers of the beans to aids in digestion. Beans are naturally high in fiber something which is painfully lacking in many western diets.

Neil Meyer
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    Im pretty sure they debunked the 'add salt/acid at the end, otherwise beans don't cook properly' - there have been plenty of people test this out, – nr_aus Aug 31 '21 at 02:17
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    "Maybe the women in your family would shocked because they had the practice of soaking beans in bicarbonate of soda." Nixtmalized beans? – nick012000 Aug 31 '21 at 08:52
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    Nick: different reason, you use baking soda to soften the bean skins. It's particularly common with chickpeas. – FuzzyChef Sep 01 '21 at 00:41
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    "If you don't do that you get hard and cooked beans, which goes down about as easy as eating car tyres." This is untrue in my experience. – Daron Sep 01 '21 at 12:02
  • I only use a few kinds of beans so my experience is limited to those but I add seasoning and other ingredients during cooking all the time and never had hard beans. I always soak beans for 8+ hours. – xxbbcc Sep 02 '21 at 13:37
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When preparing lupin, the water used to soak them in should be discarded, and even this should be done several times, or it has a bitter taste.

Wikipedia page states that if not prepared correctly, lupin can be toxic.

(This is answer is community wiki so knowledgeable people can improve it. :-) )

Pablo H
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    Raw red kidney beans also contain toxins, and should be boiled and the water thrown away to make them edible. Canned kidney beans are less hazardous however because they are pre-cooked, and eating the juices from the can won't kill you. – Robyn Sep 01 '21 at 04:20
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The soaking water does not make a difference in the case of beans. Soaking is osmosis between beans and the soaking liquid, nothing comes out of the beans themselves, that is if they don't contain pesticides or other chemicals. The liquid is generally thrown just because it is sitting in open for hours and may contain dirt or impurities.

However, while soaking rice, you should really wash the rice thoroughly first (until the water runs clean) to get rid of the starch and discard the water if soaking is required.

abhinav-shawarma
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  • After soaking beans, the water usually takes on quite a bit of color - and more color for longer soak times. And some flavor, if you taste it. This seems to contradict your "nothing comes out of the beans themselves". Do you have any sources to support your claim? – Gregor Thomas Sep 02 '21 at 01:44
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hmmm. I honestly thought this was crazy talk when I read it.
But I give these guys a pretty high reliability estimate:

https://www.fda.gov/food/metals-and-your-food/what-you-can-do-limit-exposure- arsenic

Now that I think about it, Utah, where I live, has some places with a pretty high arsenic content in the soil. Of course, we don't have enough water to grow rice.

Randolph Howell
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Is there ever a case when one should dispose of the soaking liquid rather than use it as additional flavoring to a stock

YES! YES! YES!

Extract from FDA PUBLICATION May 13, 2014 Arsenic in Rice and Rice Products Risk Assessment Report (Revised March 2016) | 2

We knew that arsenic was present in a variety of foods in the U.S. diet but until recently there were not enough data to determine the amount that is inorganic versus organic. To provide information for our estimates of dietary intake of arsenic from rice and rice products, we measured the arsenic levels in these foods. We found that average concentrations of inorganic arsenic – the more toxic form of arsenic – were as follows:

• 92 parts per billion (ppb) in white rice

• 154 ppb in brown rice

• 104 ppb in infants’ dry white-rice cereal

• 119 ppb in infants’ dry brown-rice cereal

Sorry for getting so excited but......Well I am absolutely amazed by both "The question" and "The answers."

Obviously, our health advisors are missing their target with "Stack Overflow" users.

Soak your rice overnight – this opens up the grain and allows the arsenic to escape. Drain the rice and rinse thoroughly with fresh water.

How to Cook Rice to Remove the Most Arsenic

I think this article says it all really, and rice being the main offender does not mean we can just exclude beans & pulses. Personally, I find the statement on organic rice "Whether rice is grown organically or conventionally does not have an impact on arsenic levels" particularly interesting.

Brad
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    Pretty sure that if rice had any significant amount of arsenic in it, it wouldn't be allowed to be sold. Reducing a quantity that's basically zero by 50% or 80% doesn't really make a difference, because it's still basically zero. – nick012000 Aug 31 '21 at 06:59
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    there was a recent study done by a University in Ireland and reported in Yahoo News on this subject and actually, it is quite worrying. If you eat rice often, that is. But in any case, it is a very good reason to not recycle the soaking water. – Brad Aug 31 '21 at 07:07
  • @nick012000 In April 2016, the FDA proposed an action level, or limit, of 100 parts per billion (ppb) for inorganic arsenic in infant rice cereal. The FDA also developed advice on rice consumption for pregnant women and the caregivers of infants. But as rice and its products (rice cakes, rice milk, et cetera) continue to feed more than half of the world's population, **people beyond infants and pregnant women who eat rice on a regular basis should be concerned**. So no it is not 80% of zero – Brad Aug 31 '21 at 07:15
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    "In April 2016, the FDA proposed an action level, or limit, of 100 parts per billion (ppb) for inorganic arsenic in infant rice cereal." Like I said, basically zero. Unless you're eating multiple kilograms of rice, it's not a big deal. – nick012000 Aug 31 '21 at 07:16
  • @nick012000 The US National Research Council has noted that as many as 1 in 100 additional cancer deaths could be expected from a lifetime exposure to drinking water containing 50 μg/L The FDA proposed an action level, or limit, of **100 parts per billion (ppb) is equivalent to 100 μg/L** so it is not insignificant as using 2017 figures 9.6 million people died from cancer. Using the lower 50 μg/L figure this would amount to a **yearly total equal to 1.5 times the total number of official Worldwide Covid-19 deaths to date**. – Brad Aug 31 '21 at 08:47
  • The important thing is how much is consumed. People drink litres of water each day - but people in the West don't eat kilograms of rice a day. Just checking some prepackaged rice in my pantry, a single serving of rice is about 125 grams. – nick012000 Aug 31 '21 at 08:49
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    @nick012000 so 125g rice with 100ppb, would be equal to 10% of your 50 μg/L per day. – Brad Aug 31 '21 at 09:03
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    Welcome to SA, Brad! However, I'm afraid that I've -1'd your answer, because you are offering specific food safety advice without linking to a reputable source of this advice. If you can fix your answer to link to advice from recognized food authorities, I (and others) will likely upvote it. Thanks! – FuzzyChef Aug 31 '21 at 18:22
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    @Brad "50 μg/L" -- but how many liters of water are you supposed to consume in a day? (Probably more than 1, especially if you include water used in cooking.) And that's every day over a lifetime. Even in areas where rice is a staple, I think you might be at more risk from obesity at that point. – user3067860 Aug 31 '21 at 20:31
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    @Brad - by your own calculations (125g rice with 100pp => 10% of daily limit), I can eat 1.25 *kilograms* of uncooked rice *per day*, and *still* be at the safe level. Cooked rice weighs about 3x the raw weight, thus one can eat 3.75kg (8.3 pounds) a day, without concern. It's not really cause for "worrying". – Kingsley Aug 31 '21 at 22:27
  • @nick012000 Re "if rice had arsenic it wouldn't be allowed to be sold", here's my rant. I've seen this argument: that because X is regulated, if it sold, then it is safe. First, (given, or assuming, this site audience is worldwide) perhaps in other countries X is not regulated, or not stringently so. Second, even if X is regulated, it may happen that _some_ X is sold even with over-the-limit toxins/contaminants, knowingly or unknowingly. Even in the U.S. there are [examples](https://en.wikipedia.org/wiki/Flint_water_crisis). So "is X toxic?" is not definitely solved by "no, because regulation" – Pablo H Sep 01 '21 at 13:57
  • @FuzzyChef please see the amended answer with the FDA attachment. I should have done this before. However, it is quite an old document. Knowledge about this subject has been around for years I thought everyone but the "poster" was aware of the Arsenic in the food situation. – Brad Sep 03 '21 at 03:21
  • Thanks for the FDA report link, but it's not really making your case for you: "The model predicts 39 cases per million (median estimated lifetime risk of lung and bladder cancer) from consumption of all rice grain and rice products. FDA calculated that this is a small portion of an estimated 90,000 cases per million of lung and bladder cancer cases in the U.S." Arsenic from rice sounds like a shark-attack level of risk. – FuzzyChef Sep 03 '21 at 06:06
  • @FuzzyChef I don't surf and I live at 8000ft so Tsunami risks are pretty low as well as my fear of sharks, I also always wash and soak my rice and throw away the water. As to your comment. **Why have you chosen to completely ignore other adverse effects reported to be associated with long-term ingestion of inorganic arsenic in humans are cancer, cardiovascular disease, neurodevelopmental toxicity, adverse pregnancy outcomes, non-malignant lung disease, and diabetes (NRC, 2013). and cancers of the skin, skin lesions and ischemic heart disease** – Brad Sep 03 '21 at 08:34
  • @FuzzyChefst in case the tables turn did you realise the general population should limit themselves to eating 125g a week of Shark also tuna, swordfish, marlin, orange roughy, and escolar and in some cases 125g per month not a week. I won't bother to post the link from the Canadian Gov as you doubtless won't believe this either. – Brad Sep 03 '21 at 08:49