Why does dal foam while boiling? Should you actually remove it?

If you have ever cooked dal, you have probably seen it happen: the water starts bubbling, a layer of white or pale foam rises to the surface, and suddenly you are wondering whether something is wrong with the food. In many Indian kitchens, the instinct is to reach for a spoon and remove the foam immediately.
But is that actually necessary?
The short answer is no. The foam that forms while boiling dal is generally a natural result of cooking pulses and is not, by itself, a sign that the dal is dirty, spoiled or unsafe to eat. Scroll down to read more...

The frothy layer is largely a combination of compounds released from the pulses into the cooking water. These include proteins, starch and naturally occurring compounds called saponins. As the dal boils, heat and movement help these compounds interact with air and form bubbles that collect on the surface.
Saponins are particularly interesting because they have surface-active properties, meaning they can help stabilise bubbles. This is one reason pulses can produce noticeable foam while cooking. Research has also shown that pulse proteins can contribute significantly to foaming properties.
​A 2023 study published in National Library of Medicine, which examined foam formation in faba-bean cooking water, found that both proteins and carbohydrates contributed to its ability to form foam. The same principle helps explain why cooking water from pulses can become surprisingly frothy.

There is no good evidence that the foam itself is something you need to remove for safety. The idea that the foam represents “toxins” or impurities coming out of the dal is an oversimplification. Pulses naturally contain several compounds, including saponins and other substances that can be reduced through soaking and cooking. But that does not mean the visible foam is a concentrated layer of harmful substances.
In fact, cooking is an important part of making pulses easier to digest and reducing several naturally occurring antinutritional compounds. A review published in Legume Science notes that cooking can substantially reduce compounds such as trypsin inhibitors, tannins, phytates and saponins in pulses. It also explains that some water-soluble compounds can move into the cooking water during processing. The researchers highlighted cooking, soaking, dehulling, germination and fermentation as useful processing methods for reducing these compounds and improving the nutritional quality of pulses.

There is a perfectly practical reason: appearance and texture. As dal simmers, proteins, starches and naturally occurring saponins can rise to the surface and form a pale, frothy layer. Saponins are known for their foaming properties, which helps explain why certain dals produce more foam than others. The amount can also vary with the type of pulse, how thoroughly it has been washed and the cooking method. Some cooks prefer to skim the foam because it can make the cooking liquid look cleaner. Depending on the type of dal, it may also carry some of the compounds that have leached into the water, along with tiny particles from the pulses. Removing it can therefore be a matter of preference rather than a mandatory safety step.
The appearance of this foam can sometimes make a pot of dal look as though something has gone wrong, but it is usually simply a natural part of cooking pulses. Rinsing the dal thoroughly before cooking may reduce some of the surface material, although it does not always prevent foaming completely. Pressure cooking, simmering and the amount of water used can also affect how much foam appears. In traditional kitchens, cooks often judge the dal by its aroma, consistency and colour rather than treating the foam itself as a problem. Whether you skim it or leave it alone ultimately depends on the texture and appearance you prefer.
If you are making a particularly smooth dal, removing the foam can also give you a cleaner-looking finished dish. But if you leave it in, there is generally no reason to panic. Once the dal cooks, the foam usually subsides and gets incorporated into the dish.

Not necessarily. This is where the common kitchen belief needs a little nuance. Saponins and other compounds can be reduced through cooking, soaking and draining, but the visible foam cannot be treated as a precise measure of how many unwanted compounds are present in your dal.

A 2017 review published in ScienceDirect found that processing and cooking can promote the loss of saponins from pulses. The researchers also noted that saponins are naturally occurring compounds in edible legumes and that their effects are more complicated than simply labelling them as “bad.”

You can, but you don’t have to. If you like your dal looking clear and smooth, skim the foam during the first few minutes of boiling. If you are cooking dal for an everyday meal and don’t mind the appearance, you can simply let it cook.
The more important steps are washing the dal properly, using adequate water and cooking it thoroughly. Soaking can also help with cooking time and may reduce some water-soluble compounds.
The next time your dal starts producing that familiar white foam, there is no need to treat it like an emergency. It is mostly a visible reminder of what makes pulses such interesting foods: their proteins, starches and naturally occurring plant compounds are interacting with heat and water right inside your pot. In other words, you can skim the foam for a cleaner-looking dal, but you don’t need to remove it because you think it is poisonous or unhealthy.