When to salt idli batter

A saying in Tamil goes, “Uppillaa pandam kuppaiyile”. Which means ‘unsalted food belongs in the dustbin’! Usually mild-mannered, this culture has used such strong language to indicate the importance of adding salt to food. And for good reasons… Salt is typically added in tiny amounts to most dishes. Yet, it performs many roles.

Saltiness is one of the five basic tastes that we humans can detect. And there are reasons why we evolved the ability to detect this taste. Salt is an important source of sodium which (along with other metals like calcium) helps give our bones their structure. The sodium and chlorine in salt also carry electric charges and act as electrolytes in our body, helping our cells to communicate with the brain using electricity. But too much salt will disturb this electrolyte balance. So we need salt, but not too much. Which is why our brains are wired to make us like foods that are salted just the right amount. Use less salt and the food tastes bland. Use too much, and the food starts tasting bitter!

Apart from being a basic taste, salt also affects how we perceive other tastes. You might have noticed how adding salt to bitter gourd slightly reduces the bitterness. But adding a tiny bit of salt to sweet dishes enhances the sweetness! If you are curious about this and would love to know more about the basic tastes, The Flavor Equation by Nik Sharma is a great book to start with. 

The most surprising thing is, for the tiny amounts we add, salt affects not only the taste but in some cases it affects the texture of the dish too! In the case of idli batter, the key questions are: “When is the right time to add salt? Before fermentation or after fermentation? And how much salt is the right amount?” I did some experiments to find out.

Salted Vs Unsalted Idli Batter

In one of my previous experiments, I mixed rice and urad dal batter using four different methods to find out which mixing method gave the best results (TLDR: hand-mixing won!). For each method, I also made a salted sample and an unsalted sample –  to see if there is any difference between adding salt before fermentation and after. Here is what I observed:

Method 1 – Mixing with ladle

Before fermentation:

After fermentation:

Method 2 – Mixing with whisk

Before fermentation:

After fermentation:

Method 3 – Mixing with hand

Before fermentation:

After fermentation:

Method 4 – Mixing in the grinder

Before fermentation:

After fermentation:

Here are the samples side-by-side, for a quicker comparison of the volume increase after fermentation:

Notice how the unsalted samples have risen more in volume after fermentation (except for hand-mixing, where both salted and unsalted samples have risen the same amount). Also, the unsalted samples have slightly bigger and fewer bubbles than the salted samples. What causes these differences? And does the higher volume mean that fermenting the batter without salt is better? Maybe not.

What Causes These Differences?

Before we understand the effect of adding salt to idli batter, consider the process of fermentation for a moment. When a batch of idli batter is ground and set to ferment naturally, there are scores of microbes that begin feasting on the batter. These microbes come from the ingredients (especially the surface of the urad dal), from your hands, from the grinder (ones that survived the washing after the previous batch), from the air, etc. It has been found that there are at least 290 different species of bacteria alone that are involved in the process. While all these bacteria might digest the nutrients in the batter and produce different products, not all of them are beneficial to us. Some of them are even harmful. So, the goal for us is to nurture the most beneficial microbes and hinder the harmful ones from growing. This is managed beautifully by adding salt, because salt affect different microbes differently.

The bacteria that is most helpful in the initial stages of fermentation is called Leuconostoc mesenteroides. It can tolerate high salt concentrations, and this gives it an advantage over other less tolerant species. Because of this advantage, L. mesenteroides can begin metabolism faster. In the process, it produces lactic acid, which further inhibits the growth of non-desirable organisms. In course, it also produces carbon dioxide which replaces the oxygen present in the batter. (Oxygen is present in the air bubbles introduced during initial aeration when urad foams up and later on when you whisk the batter to mix. Oxygen is also present in dissolved form in the water present in the batter). This makes the environment anaerobic and unsuitable for the growth of subsequent species of lactobacillus which are not desirable. 

Another helpful bacteria is E. faecalis, which is responsible for lowering the pH of the batter in later stages of fermentation (after L.mesenteroides has done its work). This lower pH is what makes the batter sour and gives idlis their characteristic sour-sweet taste. Thankfully, E.faecalis is also tolerant to high salt concentration. So, adding salt to the batter before fermentation gives these two desirable species an advantage over the others.

There are some other undesirable spoilage microbes which too can tolerate high salt concentrations. But the acidic environment created by L. mesenteroides and E.faecalis keeps the spoilage bacteria at bay (rather than the addition of salt itself).

So, why did the unsalted samples rise more in volume? And is that an advantage?

Apart from making the batter safer by keeping undesirable microbes at bay, salt plays another role too. It draws out water from the microbes (even the beneficial ones) and slows them down. This slow rate of fermentation may result in slightly lesser volume at a given point in time. But this slow pace allows the development of complex flavours and gives a better taste to the idlis.

Also, the bigger sized bubbles (caused by uncontrolled fermentation by multiple microbes) in the case of the unsalted samples are actually a disadvantage. They will get broken down much more easily when you salt and stir the batter after fermentation.

To illustrate this, here are my samples just before preparing to steam them (ie., just before salting the unsalted samples and stirring to mix the salt in) :

Now, I added salt to the unsalted samples and stirred them to mix the salt into the batter thoroughly. This made the batters deflate even more than the pre-salted samples.

You may think you could hold on to these bubbles by not stirring the batter before steaming. But while steaming, these big bubbles expand too much early on and escape during steaming and cause the idlis to fall back flat. So in any case, the bigger bubbles and the resulting higher volume of unsalted samples turn out to be clear disadvantages.

Effect of Salt in other fermented products

Salt affects not just the fermentation of idli batter. This happens with pickled vegetables (where too, L.mesenteroides is the hero). It also affects bread dough (where yeast is the main fermenting agent used commonly). The difference between salted and unsalted bread dough is beautifully shown by Chain Baker in his blog post:

In this case too, we see almost the same differences as we saw in idli batter:

• The unsalted bread had bigger but lesser bubbles
• The salted bread has smaller but more number of bubbles; Also notice that it has a slightly higher rise in volume compared to the unsalted version
• Too much salt (the 10% sample)  prevents fermentation from happening at all.  Because of the absence of fermentation, there are no bubbles and the ‘bread’ has a dense structure. 

Hence I don’t see any advantage in not salting the batter before fermentation.

My Recommendation

Salt your idli batter before fermentation. The ideal amount is to add 1% of salt, measured by the weight of the final batter. In other words, for every kg of batter, add 10 gm of salt. If you don’t want to be bothered by weighing scales, a quick thumb rule is to use 1 tsp of crystal salt for every cup of dry rice and urad grains you started with. A very convenient way to do this is to add the salt into the grinder itself when rice is being ground. This will ensure that the salt gets mixed uniformly into the batter too.

References:

1. The Flavor Equation book by Nik Sharma
2. Fermented Fruits and Vegetables – A Global Perspective by Mike Battcock and Dr. Sue Azam-Ali
3. Role of Leuconostoc mesenteroides in Leavening the Batter of Idli, a Fermented Food of India1 S. K. MUKHERJEE, M. N. ALBURY, C. S. PEDERSON, A. G. VAN VEEN, AND K. H. STEINKRAUS New York State Agricultural Experiment Station, Cornell University, Geneva, New York, 1964.
4. Chain Baker’s blog post and video on how salt affects bread dough.