Why Sous Vide dried Beans?

Cooking Beans

I was surprised, recently, to find that beans could be Sous Vide cooked… So I looked into it and found that they are possibly best Sous Vide cooked. Here are some of my notes. I hope they are useful to someone. It would be good to hear other views.

A lot of this information is from “McGee on Food and Cooking” pp 486 – 488.

Windy Beans:
Flatulence is caused by two different indigestible carbohydrate groups which make it into the large intestine where the biom produces CO2 and Hydrogen.

Soy, Harricot and Lima are particularly high in these carbs. (I expect their close relatives Canellini and Flageolet may be similar in this).

The carbohydrate group found as cell wall cements produce the same amount of gas in the gut, but they exist in much higher quantities.

The first group of carbohydrates, is found in lesser quantities, is water soluble. So soaking beans and throwing away the water will reduce them to a degree. However this is at the cost of: soluble vitamins; minerals; simple sugars; seed coat pigments; flavour and antioxidants. (“High price”.) So beans are best cooked in just enough water for them to absorb and cook. This means the cook does not use vigorously boiling water as they might with vegetables. Putting beans into water on a rolling boil can damage seed coats and caust the bean to break down into a mush. So too does stirring the pot.

Slow cooking breaks both of these carbohydrate groups down into simple sugars. 180–200 deg. F / 80–93 deg. C works well.

Beans will absorb water more slowly at first if it is salted, but the bean is then seasoned throughout. It makes little difference to the overall cooking time. The beans will absorb the water. It is a myth that salting the water makes beans tough.

Cooking Water / Medium:
Hard water with high levels of Calcium and Magnesium soften the cell walls and can make the beans mushy, Whereas an acidic cooking medium reinforces the cell walls. Acidic mediums can slow or even prevent the beans from softening fully. Sugar re-enforces the cell walls and it slows the swelling of the starch granules. So tomatoes which have sugars and are acidic can actually preserve the bean structure during prolonged cooking – baked beans.

Soaking beans reduces the cooking time by 25% because the beans have re-hydrated and a lot of the cooking time is waiting for the beans to re-hydrate. Additionally the long cooking times can lead to the outer bean being overcooked and breaking down. Though soaking depends on temperature and pressure a rough guide at sea level is that beans absorb about ‘more than half of their total water capacity’ in the first two hours and they reach their original weight in 10 – 12 hours. Blanching the beans for 90 seconds in boiling water and then soaking them in cool water reduces the soaking time to 2-3 hours because the blanching rapidly hydrates the seed coat which controls the water absorption of the bean.

Salt and Baking Soda:
Both shorten cooking time when they are added to the soaking water. Salt at 1% reduced cooking time greatly. Baking Soda at 0.5% reduces the cooking time by 75%.

The alkalinity of the baking soda imparts a slippery mouthfeel and a soapy taste to the bean.

Salt reduces the swelling and gelation of the starch granules and this lesds to a mealy texture rather than a creamy one without the salt.

Persistently Hard Beans:
Some batches take much longer than usual to soften, or never do quite soften. This can be caused by high growing temperatures or low waterfall during growth. Thr coat on these beans becomes unusually water resistant. These beans a generally smaller than the usual ones and so they can be avoided. These are called ‘Hard Seed’.

‘Hard to cook beans’ might become so by long storage or storage in overly warm or humid conditions.

Cooking Times:
Douglas Baldwin gives the following times
1 Cup 250ml Beans
3 Cups 750ml Water
1 Tsp Salt (!)

Cook at 195 deg F / 90 deg C

Black Beans 3.5 – 4.5 Hr
Cranbery Beans 2.5 – 3.5 Hr
Chickpeas 5 – 6 Hr
Great Northern Beans 3 – 4 Hr
Navy Beans (Haricot) 3 – 4 Hr
Pinto Beans 4 – 5 Hr

Kate Williams recommended using canning jars instead of bags – This seems like a really good idea – Thanks Kate!

Be great to hear others views on this topic.


I’ve not done beans. I have done Du Puy lentils at Christmas time.

When I looked for information I found recommendations ranging from the 190F for 6 hours to 196C for 90 minutes and 183F for 12 hours and a whole lot more.

Vegetables cook at 183F (pectin conversion point) so the temperature had to be at least that. I decided to go for 186F and start with 90 minutes. Lentils were washed and placed in a quart Mason jar. 1.5 cups of lentils to 2 cups of stock, some bay leaves and thyme (I don’t usually add herbs to a sous vide cook, but seeing as it was over the vegie temperature). No salt, because my stock had been salted when I cooked it.

After 30 minutes in the jar I was a little concerned that I’d over filled the jar, but it turns out all the swelling happens in the first 30. I checked the lentils at 90 minutes and found them cooked, but still a little firm for my liking and decided to give them another 30 minutes. I got caught up in other things, so by the time I checked the lentils again it was 2 hours later. The lentils were softer, still with some bite. As I wanted them for a salad this was fine for me. I drained a bit over half a cup of stock from the jar and 1 quart of lentils.

I will try them again and give them more time, perhaps overnight. I find there is such a brief time between cooked to perfection and mush doing them the traditional way that it’s worth testing this way further.

I have no doubt that they could be cooked to a point where they no longer maintain their structure, but I’ve a sneaking suspicion it would require way more than 24 hours to do it.

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A word on toxins:

Kidney Beans (Lima Beans to a lesser extent):
These contain lectins (phytohaemagglutinin) which produce hydrogen cyanide which is very toxic and can kill.

When ‘cooked’ at low temperatures (up to 176 F or 80 C) these toxin levels can increase five fold.

In order to destroy the toxin phytohaemagglutinin that occurs naturally in kidney beans, the NHS (U.K.) and FDA (U.S.) both advise that the beans should be soaked for at least 12 hours, drained and rinsed. The toxin is water soluble and quite a bit of it leaches into the soaking water.

They should then be covered in fresh water and boiled vigorously for at least 10 minutes. This destroys the remaining toxins.

It is then safe to cook at a simmer ( 45-60 minutes) or by other low temperature methods.

Ember - Thank you - I found that helpful.

This is plain silly because the beans won’t cook below 83.4C/183F. They’ll always be indigestible hard centred bullets.

Everything we consume has the potential to kill. Even oxygen that we need for survival is a poison. It’s all about understanding and mitigating risk.

No Ember its definitely not silly.

The beneath 80 deg C was an interesting aside which becomes relevant were one to heat them slowly (cold sous vide bath coming up to temp. slowly) which might X5 the lectins and then if one goes on to sous vide them at say 90 deg C they will cook, but the lectins will not be destrotyed. One authority reckoned that 5-10 beans with these levels would be fatal.

The meat in the message is how to destroy the lectins which will produce hydrogen cyanide which is a lethal poison. Once in the body there is no way of removing it.

Sous Vide cooking these beans will not destroy the lectins.

Which is why I posted this information.

Sorry, I didn’t mean the information was silly. I meant the idea of someone holding beans at 80C was silly, but then… if you don’t know 83.4C for vegetable cooking this is quite possible.

I’d think the long term 80C is more likely to be a hold warm problem than a cook problem though. Or even a slow cool. If someone were to leave jar or bag in the bath after cooking and let them cool with the bath water. Power or device failure style.

I can vaguely recall seeing a problem with re-warmed rice too. Something that ready meal manufacturers had to treat against. I must look that information up.

No problem and I take your point.

Thanks for prompting me to revisit rthe rice issue.

This is from the NHS:

"…you can get food poisoning from eating reheated rice. However, it’s not the reheating that causes the problem, but the way the rice has been stored before it is reheated.

Uncooked rice can contain spores of Bacillus cereus, a bacterium that can cause food poisoning. The spores can survive when rice is cooked.

"If rice is left standing at room temperature, the spores can grow into bacteria. These bacteria will multiply and may produce toxins (poisons) that cause vomiting or diarrhoea.

The longer cooked rice is left at room temperature, the more likely it is that the bacteria or toxins could make the rice unsafe to eat.

If you eat rice that contains Bacillus cereus bacteria, you may be sick and experience vomiting or diarrhoea about one to five hours afterwards. Symptoms are relatively mild and usually last about 24 hours."

However cooking starchy foods and allowing them to cool converts about 30% of the starches to indigestible starches which are very good for the gut flora and fauna and they lower the products glycemic index. But as they say, that is another story.

Useful discussion about beans. It’s ironic that we fuss so much about eating man-made pesticides contaminating our fruits and vegetables but largely ignore the natural and quite toxic pesticides that are the same plants use to protect themselves from pests. Fortunately our cooking methods can render most of them inactive.

Just to clarify, beans have lectins, phytohaemagglutinins and phytic acid but no cyanide. Fruit seeds containing prussic acid are the main source of veggie cyanide but we don’t usually eat them.

Lectins and phytohaemagglutinins are the main glucoproteins to be concerned about as far as actually toxic problems are concerned (phytic acid mostly just interferes with digestion and nutrient absorption). As with all things SV, it’s all about time and temperature. If you presoak for 5 hours in lightly salted water or broth (optional but I find it makes a better bean except for black and pinto beans) and cook them at 190F (88C) for at least an hour (usually much more) until they are creamy but still firm, you can’t go wrong.


Thanks for the info.

I am just at the stage of trying sous vide beans and lentils rather than traditional methods.

I perhaps wrote my post poorly - According to H McGee - the lectins are Hydrogen Cyanide forming. I agree - there is no cyanide in the beans before improper cooking.

I tend to eat Flageeolet, Harricot and Canellini beans, which are not much of a problem with toxins. I like McGees idea of a vigorous boil to speed up the soaking.

I think for me though I will stick to the UDA / NHS advice about boiling any other bean first to break the toxins down.

I guess its like all things, we make our different choices.

I will try your method with some falgeolet today - I just fancy some of those.


McGee must be referring to raw lima beans which are the only ones that contain cyanide bound in a sugar compound, although the ones grown in USA and Canada have had the levels bred down to pretty low levels. It’s harmless on it’s own but when chewed it mixes with an enzyme in the bean that releases hydrogen cyanide. Heat destroys the enzyme rending them safe to eat after cooking.

What I love about SVing beans is once I figured out the times for each individual bean after a soak, I can put 4 or 5 jars of different types of beans in the water bath, turn it on, set the timer for the quickest cooker, and just leave them. I pull each jar at it’s time and voila, perfect beans that I didn’t have to watch on the stovetop. Very liberating.

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I’m going to try that and then freeze them.

What I want to do is increase the quantity of beans and lentils in my diet, but I tend to plan my meals daily and don’t want to do overnight stuff.

Overnight doughs are quite enough.

BTW - Thanks for your input - I’ve found it helpful.