Bean Science Part I

The Science of Cooking Beans

Bean Science

From how to cook them better and more efficiently to the issue of farting, aka flatulence, to pectins and lectins, beans are a popular conversation piece. In part one of Bean Science, I will focus on cooking beans and the science behind the methods. Next time, we’ll dig even deeper, and I’ll answer some of the most common and popular questions I’ve received. (If you’ve got more questions, leave them in the comments below, and I will share their answers in part two). I’m also going to address some of the common myths surrounding beans. Now let's first take a closer look at the bean and how to cook it.

The Bean

Beans belong to the Legume or Leguminosae family of plants. Dried chickpeas, split-pigeon peas, and peas aren’t beans, but they belong to the same family of plants, and luckily that means a lot of the cooking methods that apply to beans are also applicable to chickpeas. Lentils, the other member of the legume family, are thinner by comparison and much smaller; they cook fast, so you don’t need to soak them, and except for cooking them in lightly salted water, you shouldn’t need to do much else.

Beans are rich in proteins and fiber, easy to grow, and an excellent and economical source of protein; they also taste pretty darn good when cooked properly. There’s a reason why a bowl of chili, baked beans, or dal is comfort food; that unmistakable creamy tender texture is pure joy.

Why Beans Turn Hard on Drying

When dried beans are stored for a long time, kept at high temperatures and high humidity, the seeds become harder, making them take a long time to cook. Besides losing their water content, the drying process also kicks off chemical changes inside the bean. One of these changes involves accumulating a lignin-type material (lignin is a structural carbohydrate, and wood contains lignin, so that should indicate how hard beans can get). The second change takes place with another carbohydrate called pectin. This is why older dried beans often take painfully long to cook. Cooking methods for dried beans involve manipulating pectin’s chemistry and hydrating the bean.

A term often used in bean research is HTC or the Hard-To-Cook phenomenon. While all dried beans experience the HTC effect, the degree to which they display this phenomenon varies; for example, kidney beans take longer to cook than black beans. You might also come across ETC or Easy-To-Cook, a term used to distinguish between beans that cook faster, like black beans.

Bean Chemistry and The Hardness of Beans

Pectin is a carbohydrate found in plants, and it provides structural integrity to cells by acting as the glue holding them together. I’ve come across some articles that refer to pectin as a type of complex starch; it is not a type of starch and is chemically very different. Starch is a glucose polymer and acts as the bank reserve for the plant’s energy needs; pectin is a polymer of D-galacturonic acid, contains some other types of sugars, and is the cement that holds plant cells together. I’ll return to the relevance of the chemical structure of pectin a little later.

In cooking, pectin is used to help set jams, jellies, and marmalades. Pectin can form gels in water, and jam recipes utilize this principle. As pectin forms a gel on cooling, it binds water and reduces “water activity.” Low water activity reduces water availability for harmful bacteria and yeast to grow and jams last longer. Pectin is also essential in vegetables and fruits like potatoes, beans, and quince because it gives them hardness, and recipes are designed to work on the pectin and make the vegetable and fruit softer.

There are two ways to help dried beans cook faster and taste better.

1. Hydration - Soaking dried beans in water helps the outer coat of the seed turn tender, and consequently, the bean fully absorbs the water. The hydrated bean then cooks faster.

2. Manipulating the Chemistry of Pectin - Pectin can bind two metal ions - calcium and magnesium. Combined with the chemical changes that occur in pectin during drying, the bean gets very hard. Getting rid of calcium and magnesium makes the pectin soluble. Earlier I mentioned that pectin is made up of chains of D-galacturonic acid. Pectin also contains another sugar called rhamnose and small quantities of the sugars D-galactan and arabinan. All these sugars are held together by chemical bonds and interfering with those bonds can make pectin unstable and more soluble. Acids like citric acid break one type of bond in pectin (glycosidic bond), while alkalis like baking soda can damage two bonds (ester and glycosidic bonds).

Salt and Baking Soda

One way to remove the calcium and magnesium ions inside pectin is to brine the beans or cook them in water containing salt (sodium chloride) and/or add a tiny quantity of baking soda (sodium bicarbonate). The sodium from these ingredients pushes the calcium and magnesium out of the pectin, and the pectin becomes water-soluble. The cells inside the bean are now loosely held together, making it easier for the bean to cook quickly. Baking soda is also an alkaline ingredient. When it dissolves in water, it raises the pH and attacks two types of chemical bonds (ester and glycosidic bonds) that hold the pectin molecule together.

Citric Acid

There’s a common misconception that you should use an alkaline ingredient like baking soda to help beans cook faster and if you need to add acids, add them after the beans are cooked. This is not true. People do use acid when pectin is involved. When making marmalade and jams, the fruit is cooked in an acidic sugar solution (typically, that acid is citric acid, the same acid present in lemons and limes, and many other fruits like apples and mangoes). Acids like citric acid decrease the pH and break one type of bond in the pectin (glycosidic bond) molecule making it weaker, and this helps the bean cells fall apart. DO NOT USE VINEGAR when cooking beans; STICK TO CITRIC ACID.

Citric acid does one more exciting thing. It acts as a chelating agent and what this means is that it can bind calcium and magnesium ions and lock them. Phlebotomists use this principle all the time when they collect blood. Sodium citrate, a salt of citric acid, is used to prevent blood samples from clotting and works with the same idea on the same principle. Initially, sodium citrate and citric acid are also used to extract pectin from potato waste, and in The Flavor Equation, I applied this idea to make oven-baked “French Fries.” Some cooks in the Middle East boil chickpeas with lemon juice or purified citric acid to get a smoother and creamier hummus, and you will see that method applied in the cookbook, On The Hummus Route. In my recipe for the fries, I add lemon juice (a source of citric acid) and baking soda to the water; the two ingredients react to produce sodium citrate, and then I boil the potatoes in them until they’re just tender. The potatoes are drained and then baked in the oven to make fries that are crispy on the outside and creamy on the inside.

Here are two ways to cook beans with lemon juice or citric acid:

The Lemon Juice Method:

For every ½ lb/ 230 g of dried beans, add 1 tsp fine sea salt + ¼ cup /60 ml lemon juice + 4 ½ cups/1 L of water. Bring to a boil, and then simmer covered until the beans are tender.

The Sodium Citrate Method (I prefer this one, it gives the best texture):

For every ½ lb/ 230 g of dried beans, add 1 tsp fine sea salt and ¼ tsp baking soda + ¼ cup /60 ml lemon juice + 4 ½ cups/1 L of water. Bring to a boil, and then simmer covered until the beans are tender.

How to Cook Beans

There are many ways to cook beans, and knowing when to use which method can become confusing. I recommend thinking about the final texture of the bean you want. For example, suppose I need the beans to be so tender that they’re falling apart, like in a bowl of warm chili or dal makhani (The Flavor Equation). In that case, I’ll go with pressure cooking or simmer the beans on the stove and add a little bit of baking soda and salt to help the beans achieve that texture. These methods focus on hydration and changing the chemical structure of pectin inside the bean. We will get into more detail about how all this happens in part 2 of this series on beans.

Dal Makhani from The Flavor Equation cookbook/Chronicle Books 2020. Photography and Styling by Nik Sharma

A Gentle Reminder: The cooking times listed here are averages I’ve measured at home. These ranges will vary depending on the type of bean, how old they are, how they were soaked, and the subjectivity of texture (people differ on how tender or creamy a texture they prefer).

Soaking and Brining

Soak dried beans in fresh water for 12 to 16 hours (I prefer soaking dried beans overnight and dealing with them in the morning, it requires less planning and cooking late into the night), discard the soaking water, rinse the beans under running water, and then cook them in salted boiling water until tender. Cooking times vary depending on the type of beans, with HTC beans taking longer, up to an hour or more.

Recently, I wrote about brining for Serious Eats and how it works. After much experimenting, I found that brining beans with baking soda and salt in water works best and produces the creamiest texture. The cooking time for brined beans is significantly shorter than those soaked in water.

This is my general brining formula:

For every ½ lb/230 g dried beans, add ½ oz/15 g fine sea salt + ~¼ oz/ 5 g baking soda in 4 ½ cups/1 L of water for 12 to 16 hours.

Salts weigh differently due to their particle size; I use fine sea salt at home because that’s readily available worldwide. Use this guide to convert the weight according to your salt type (these are approximate weights).

1 tsp fine sea salt = 6 g

1 tsp Diamond Crystal kosher salt = 3 g

1 tsp Morton’s kosher salt = 6 g

1 tsp coarse salt = 6 g

Boiling and Slow Cooking

My preferred method of cooking beans is boiling them in a large pot on the stove. I bring the beans and water to a boil and then simmer them until they’re tender. It’s much easier to check when the beans are done, especially if I need them soft but not falling apart. I can’t give you a cooking time because that will vary by the beans and where you sourced them from; I usually start checking for tenderness after 25 minutes of simmering.

Slow cooking is also nice because it appeals to my leave-it-forget-it mentality. However, slow-cooked beans take a long time to finish cooking, so plan out accordingly. You can speed this process up by brining your beans before slowly cooking them.

If you skip brining and soak the beans before boiling, you can add a small quantity of baking soda and salt to the boiling water.

For every ½ lb/ 230 g of dried beans, add 1 tsp fine sea salt and ¼ tsp baking soda + 4 ½ cups/1 L of water. Bring to a boil, and then simmer covered until the beans are tender.

Pressure-Cooking and Instant Pot

My mom loves her gas pressure cooker; I’m terrified of it because it blew and took out the ceiling back in our home in India quite a few times. As an adult, I’ve become a bit more comfortable yet still cautious around electric pressure cookers and instant pots. For gas-pressure cookers and instant pot cooking, I cook beans (soaked in water or brined prior) for 10 to 15 minutes under high pressure and then let the oven cool down naturally before opening the lid. ETC beans take less time to cook than HTC beans. I find 12 to 15 minutes with the instant pot sufficient at the high-pressure cooking setting. While these pressure-cooking methods are advantageous for shorter cooking times, it’s easier to overcook beans by these techniques. In some recipes like soups and dals, a bean with a texture that’s falling apart will work. In others, like a salad where beans need to be tender yet hold their shape, it might not be the best option (I prefer boiling beans for salads to watch the texture). Brined beans will cook faster than unbrined soaked beans; my cook time is usually 5 to 10 minutes with brined beans. I still run out of the room when the pressure cooker is on because I haven’t completely overcome my fear.

I don’t cook unsoaked dried beans in pressure cookers, but many folks do, and the thumb of the rule here is to double the cooking time you would typically use for presoaked beans.

Should you save the cooking water?

It depends on you and the recipe. If the recipe involved cooking the beans with spices, you might consider holding onto the water. If you're concerned about flatulence, you might consider discarding the water because that's where all those gas-producing substances leach out (more on this to come in part two).

Next time, in the second part of this Bean Science special, I’ll get into more details about why beans give us gas, the methods used to reduce flatulence, and answer questions, so if you have any questions, don’t forget to leave them in the comment section below.

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Further Reading + References :

• Food Chemistry - H.-D. Belitz, W. Grosch, P. Schieberle

• The Flavor Equation - Nik Sharma

• Jin-Shu Yang, Tai-Hua Mu, Meng-Mei Ma, Extraction, structure, and emulsifying properties of pectin from potato pulp, Food Chemistry, Volume 244, 2018, Pages 197-205.

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