Making a dosa starter

What we do (my wife is South Indian FWIW) is pretty close to this recipe: https://www.feedyourtemptations.com/dosa-recipe-using-rice-flour/    It's left overnight in a warm place.

The leavening microorganisms seem to ride along with the dal and rice (though that does not rule out the possibility more may come from other sources).  Best scientific paper I can find is

S.K. Soni, D.K. Sandhu, K.S. Vilkhu, N. Kamra, "Microbiological studies on Dosa fermentation" Food Microbiology, Volume 3, Issue 1, 1986, Pages 45-53, ISSN 0740-0020,  https://doi.org/10.1016/S0740-0020(86)80025-9. 

It reports (48, 52) that "Rice contributed bacteria belonging to five genera similar to Leuconostoc, Streptococcus, Lactobacillus, Micrococcus and Bacillus and yeasts belonging to three genera, i.e., Saccharomyces, Debaryomyces and Trichosporon. Black gram [urad dal] yielded bacteria ... belonging to Leuconostoc, Enterobacter, Flavobacter, Bacillus, Lactobacillus, Streptococcus and yeasts Debaryomyces, Torulopsis, Kluyveromyces and Candida. These results support ...findings ...that the bacteria and yeasts needed for fermentation of idli are introduced by the two ingredients (rice and black gram). ..."

"... yeasts Saccharomyces, Debaryomyces, Trichosporon and Hansenula help in the degradation of starch into maltose and glucose by producing extracellular amylolytic enzymes which are utilized by developing microbial load. Bacteria along with some yeasts are mainly responsible for the production of acid and gas from simple sugars like glucose and maltose and thus account for its fall in pH and rise in volume with the progress in fermentation. ...  Leuconostoc mesenteroides and other acid producing bacteria mainly caused the acidification and leavening of the dosa batter while the yeasts Saccharomyces cerevisiae and Debaryomyces hansenii improved the nutritional quality of the batter in terms of flavour, total proteins, amino acids, vitamins and enzymes (unpublished data). According to Mukherjee et al. (1965), Steinkraus et al. (1967), the acid and gas required for souring and the leavening action in the idli batter are produced exclusively by the activity of heterofermentative lactic acid bacteria Leuconostoc mesenteroides although there is a sequential change in the bacterial flora."

More accessible, in both senses of the word, is this account:  http://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/Idli-batter-fermentation/article15951210.ece  which also says bacteria are doing most of the work.  It sounds a lot like sourdough in that you are making a little habitat in which a bunch of microorganisms interact.  

Family lore favors dal as the key source of leavening microorganisms and cautions against over-washing it before use.

On ways to speed/regularize fermentation I found a couple of articles reporting good results from adding Saccharomyces cerevisiae, or brewer's yeast.  

There was a bakery in our city called Turtle Bakery.  It was called that because the sourdough breads rose so slowly like a turtle.  The starter was begun by placing organic grapes in a cheese cloth and suspending that into a water and flour mixure.  Organic was important since no pesticides were on the surface of the grapes to kill the natural yeasts which are on the grapes.  These yeasts entered the flour/water mixture and began the fermentation process and a starter was made.

I am american but of Indian decent (not south indian but Indian). My mother (and grandmother) tell me to use fresh yogurt to start dosa batter. (there is ALWAYS fresh cultured yogurt in my grandmothers house in India). So I either use fresh cultured yogurt or buy a new container of dosa batter from the indian grocery store and keep some as culture. For the past few months I have been making a small batch (1/2 cup lentils to 2 cup rice is the ratio I use) every 1-2 weeks. I add 1-2 spoonfuls of the prior weeks dosa batter to the new batch just prior to the fermentation step. So its not a separate starter per say but I am keeping the culture going.

As for the myths..... I've fermented dosa batter outside in the sun, in my stove (set to warm), in my instant pot (in glass, metal, etct) and never had a problem fermenting it. The one thing I do think makes sense (or at least I do it) is that I soak my lentils the night before to release the protein. I don't soak the rice (I buy rice grits from the indian store) because I am lazy. Your dosa batter will be fine. There is an added depth of flavor that can be achieved by playing with different rice ratios, adding rice flakes, but its not necessary.  

I find dosa batter the easiest.... I don't have to fuss with temperatures like I do with yogurt... and I don't have to discard starter like I do with my sourdough starter (I'm new to sourdough starter!).

I really want to make this and was wondering if any old lentils will do? I have some of the small black ones at the moment.

I still remember my very first filled dosa I had for breakfast in Bombay many moons ago. It was the spiciest breakfast I ever did have, probably because like an idiot I asked that it be made extra spicy. What was I thinking!

I have been making this for decades, and learned by watching my grandmother and mother make it.  They sat on the ground, grinding the maavu with their legs wrapped around basically a giant stone mortar and pestle.  I am South Indian and make a traditional South Indian meal of this with coconut chutney, sambar, and potato masala as filling.  The maavu can be used to make idli, which are soft steamed little cakes, prepared without any oil.  If you still have maavu left, and it begins to go "sour" it can be used for Utthapam.  In South India, we like our dosai sour and leave it sitting out for a day or two before we cook with it.

If you don't have a refernce point for "authentic" flavor, this is simple to make.  This is the recipe most of my American friends have been given by me.

Soak Urad dal, long grain rice (try with Riceland the first few batches), and fenugreek soaked together overnight.  There is no need to soak separately, or to add yogurt.  Although some people use it, it ruins it for for South Indians.  Try it both ways and see what you like.

In the morning, use a sturdy blender to grind into a fine paste (No need to use your hands).  Once you can run the maavu between your fingers and it feels smooth, add salt to your taste.  There is really no measure for this, just what you like.  A minimal amount of salt to use is 1/2 tsp.

All the blending should have made the maavu warm from the heat of the blender, this is good for fermenation!  Transfer to a large bowl that will allow it to at least double, and place in the oven (no experience with how this works without a gas oven/pilot light).  Let ir sit at least 14 - 16 hours, and you should have a big, bubbly, tangy smelling maavu.  Watch for it to grown too much.  You will have an overflowing mess to clean.

You can use it like this, but traditionally the air is all stirred out, and it sits overnight again.  The next morning you will have, as you said, a sort of tangy sourdough batter for dosai.  

Before anyone pounces on the Riceland, 40 years ago when we came here and were completing our studies, we used far worse than that.  When we moved to a big city, Riceland was all we could get, and our breakfasts were delkcious.  Even today I would never waste a basmati on this.  The flavor comes from allowing the maavu to ferment, not from the type of rice.

There is no starter, nor is any needed.  A "quick" batch will take a minimum of 24 hours to make.

If you make sourdough bread, you can do this.  Every Indian will tell you a different way to make it and you will learn what is best for you.  I'm excited for you and to hear how they turned out!

I have been making idli on and off for about 20 years, learning in each interval more about what not to do than anything else. There are lots of how-to posts, almost all of which have some "mandatory" action or ingredient that turns out to be unnecessary when you actually run the experiment.  But the cacophony of opinions unsupported by data makes it really hard to sort out what is essential, what is optional, what is unproductive and what is provably detrimental. And while I am not done yet (as you can tell from what I offer below) I have a process that consistently produce good idli (and in the hands of a skilled practitioner very nice dosa) and in the process have assembled a lot of experimental data that illuminates what is unproductive.  The technical literature is actually quite rich with quantitative and qualitative assessments that are very useful once you get past the vocabulary hurdles and translate the results back to a baseline formulation where comparisons can be made.  Thus the following is offered for critique and pushback as you see fit.  I am here to learn more than to teach.  As has been pointed out to me on more than one occasion, what I really need is an Indian mother-in-law.

Idli is a steamed dumpling made from a mixture of decorticated urad beans and short or medium grain (preferable parboiled) white rice that have been soaked, ground, and fermented.

The urad bean (Vigna mungo, black gram, urad bean, or black mapte bean), is grown in South Asia and available in your local Indian store whole with the black skin intact, decorticated whole (urad gota), and decorticated split (urad dal or sometimes white lentils).  I prefer to use urad gota that is less than two years old since the bacteria that are responsible for the fermentation decline with age (or may be killed by heat sterilization or excess heat during shipping or storage) and the gota seems to retain sufficient bacteria longer than the dal does.  The bacteria are associated with the urad and not the rice. My testing showed that I got better fermentation when I used urad gota than when I used urad dal (a preference confirmed by others as well).

Rice that is appropriate for idli needs to be a short or medium grain variety because it needs to have a high ratio of amylopectin/amylose.  A long grain rice will not produce an acceptable idli as the rice starch (high in amylose and low in amylopectin) is not sticky enough to hold everything together when it is steamed (that is also why long grain rice is not sticky).  Do not use basmati rice. A parboiled rice is the preferred rice to use.  Uncle Ben’s brand rice (converted rice) is parboiled.  Ask for idli rice at your local Indian store.  If you can’t get parboiled rice, use any short or medium grain rice that is suitable for sushi (it may be labeled as sushi rice).

Testing:

Because the age of the urad impacts the fermentation, it is prudent to check your supply to make sure that the bacterial population is robust enough to do the job for you. Wash 3T of urad and place it in a small cup or dish and cover it with 1 cm of water.  Using a piece of paper towel  remove any bubbles that are on the surface of the water including bubbles attached to the meniscus at the edge of the cup. Cover with plastic wrap and place in a warm spot (30-40°C) for 4 hours. If your urad is fresh you will find that there are fairly large patches of very small bubbles floating on the surface of the water.  If there are no bubbles, or just a few patches of bubbles, your idli will not ferment well. If the bubbles cover less than 10% of the surface after 4 hrs @ 40°C you probably don’t have enough bacteria to complete the fermentation in a reasonable amount of time (13-15 hrs).

The photo on the left below (which you can blow up to full original resolution by right clicking on the photo and selecting "open in a new tab") is a batch of very old (over 10 yrs in the cupboard) urad dal after it had been soaked for 5 hrs at 99°F.  You can see some bubbles on the surface indicating that it is not sterile, but also that it would take a long time to ferment a batch of idli.  The photo on the right is a batch of urad gota from a package purchased about one year ago after it too had been soaked for 5 hrs at 99°F.  In this case you see a nearly continuous film of small bubbles on the surface.  This is the indication of a bacterially well-endowed and relatively fresh batch of urad gota.

Washing:

There are many kinds of bacteria on the surface of the urad, some of which you would rather not have making flavor components for your idli, so wash the urad a couple of times, rubbing them between your hands to remove surface contamination, then add the appropriate amount of water and let them soak until fully hydrated (time is a function of temperature but at typical room temperature 15-25°C), 4 or 5 hours is enough.

Wash the rice a couple of times to remove any surface starch that is left over from polishing then pour off the washing water and add back enough clean water to soak the rice.

Soaking:

Both the urad and the rice need to be fully hydrated before they are ground, but the urad are supporting the growth of bacteria as they are soaking while the rice is just getting wet. So the soaking water for the urad will go into the grinder or blender.  The rice water can be used or discarded so long as the batch has enough water to grind or blend.

How much water:

The guideline on how much water to use varies with the specifics of the rice you are using.  With urad gota I soak them in 3X the weight of dry urad (for 64g of urad gota I soak in 192g of water; actually I wash 64g of urad gota and then put the wet urad in a small bowl and add enough water to make urad + water = 256g).  This assures that there is sufficient water to fluidize the urad as they are ground or blended.  It can be really messy and hard to clean up if you don’t use enough water at that point. The rice does not need as much water so I calculate the total water I need as 2.125 x (weight of urad + rice) then subtract the weight of the water that I use to soak the urad.  That is how much I use to soak the rice. But as I pointed out above, it depends on what kind of rice you use so be flexible.  The range of rice:dal ratios goes from 1:1 up to 4:1.  I use 3:1 by weight but it is a personal preference so you will want to try a few different ratios and decide what you like.

Grinding:

When the urad and rice are done soaking, put the urad and soaking water into a wet grinder or a (high powered) blender and grind until they make a very smooth paste, adding additional water (more likely for a blender than a wet grinder) so that they flow smoothly. You want the urad to be really smooth with no sandy or grainy feel.  A blender may heat up the urad so using ice water may be necessary with powerful blenders and big batches and you don’t want the urad to get above ~110°F or you may kill off the bacteria that you want to ferment the idli.

After the urad is smooth, add the rice and its soaking water and grind/blend until you reach your end point.  Now that is not a very precise description of when to stop, but some people like idli to be somewhat grainy while others demand that it be smooth, and some people add part of the rice and blend until it is smooth before they add the rest and then blend until it is just right to have a more porous idli. Again, don’t run the blender so long that the temperature of the mixture rises above 110°F, using ice water or ice if required to control it.

Fermenting:

When everything is done grinding, you can add the salt (1 to 2% of the weight of the batter – I use 1% but others like it saltier) either before the fermentation or wait until it is done fermenting and stir it in then. There is a theory that there are some bacteria in the mix that are slowed down by the salt, and some that actually grow faster when some salt is present (that would be the Leuconostoc mesenteroides which seems to prefer somewhere around 1% salt to maximize its growth rate).  I have done it both ways and don’t have enough data to suggest one way or the other as the best approach.

The temperature for fermentation needs to be above 25°C/77°F and temperature of up to 40°C/104°F speed things up.  But there are two bacteria that are sequentially in control of the process.  The first one is Leuconostoc mesenteroides which makes both CO2 ( making the batter foamy) and lactic acid (which contributes to the tart flavor but does not supply all of the required acid), and the second bacteria is Enterococcus faecalis which begins rapid growth only after the pH is lowered to around 5.25 by the Leuconostoc and produces sufficient additional lactic acid to drop the pH to below 4.5 (I have measured pH as low as 4.2 before the batter became more sour than tart).  When the Enterococcus faecalis has stopped producing lactic acid there is a third bacteria, Pediococcus cerevisiae, that can take over after about 24 hrs and contributes additional lactic acid to the batter making it unpleasantly sour and it is considered to be a spoilage bacteria.

The optimum temperature for idli fermentation probably varies over the cycle but not enough is known about the optimum growth conditions of the various constituents in a mixed culture to specify much more than a range of acceptable temperatures that produce good tasting idli. I have had success as low as 30°C and as high as 40°C and currently control to 37°C/99°F and consistently get good results so long as the urad has enough bacteria to adequately seed the fermentation.

The idli batter gets foamy and rises during the fermentation process.  Leuconostoc mesenteroides produces dextran which stabilize the foam; it also produces the CO2 required to puff it up. There is no yeast in idli and the Leuconostoc mesenteroides is the sole producer of the CO2 that inflates the batter, slowing down when the Enterococcus faecalis has produced enough lactic acid to effectively become the dominant component of the mixture.  So, when the volume increase seems to have stopped (it hasn’t but it seems that way), the batter should be at about pH 5.25, after which the Enterococcus faecalis continues to produce lactic acid.  You may stop the fermentation and make idli at any point after the batter is as tart as you like it.  Typically volume expansion is mostly complete by 12-15 hrs depending on temperature and the initial contribution of Leuconostoc mesenteroides from the urad to the mix.

While it is always gratifying to see a lot of volume expansion, there is a limit beyond which it is not terribly useful. You need about 20% volume increase to assure that there is sufficient CO2 in the batter to cause the idli to puff up when steamed, but beyond that too much CO2 will cause the idli to collapse in the middle of being steamed. So always stir down the batter before steaming until you have about 20-25% more volume than you had when you started the fermentation.  This is most important if you add the salt before the fermentation since there is then nothing that demands that you stir the batter before loading the steaming pans.  If you delay salt addition until after the fermentation is complete (or put half of the salt in before and half in after fermentation) the process will keep the idli from falling while steaming. You will learn how much batter to load into each mold so that the idli do not puff up and stick to the pan above.  You will need to rotate the pans so that successive pans in the stack are offset by enough to minimize the inclination for them to become stuck to the pans above and below.

Steaming:

After you have greased and loaded the pans, and stacked them as appropriate, put the rack into your steamer and steam for 10-13 minutes. Then take the lid off and remove the rack to somewhere that the idli can cool off enough to let the starch crystalize (about 5 min) so that you can separate the racks without ripping big chunks of idli that are stuck to the pan above.  This will happen when you separate the pans too early. If you wait, the idli will separate cleanly and the pan will leave a dimple in the top of the idli in the pan below.

Serving:

Remove the idli from the steaming trays with a small flat spatula or silicone scraper, or anything you can slide under the edge of the idli to get them out of the pans.  Transfer the idli to a plate and serve warm with coconut chutney or sambar (or whatever your specialty is).

After notes:

You may note that I have not included any fenugreek in the idli even though many people do.  I do not particularly care for the flavor and after a lot of experiments found nothing to support a claim that it is needed.  I thought for a long time that it was essential for either bacterial growth or as a thickener or thixotropic agent.  It turns out that the bacteria don't care and produce sufficient dextran to stabilize the batter foam.

The other practice which I now put in the category of wives' tales unsupported by experiment is that there is something about mixing the batter with your bare hands that contributes to successful fermentation.  If your hands are clean enough to put into the batter, they don't have anywhere near enough bacteria to impact the fermentation, and if your hands have enough bacteria on them to make a difference, then you don't want to put them into a batter that may encourage the propagation of contaminants.

The water you use needs to be good enough to drink and should not have so much residual chlorine that it kills off the bacteria you depend on.  I use reverse osmosis filtered water with an activated carbon pre-filter to get rid of any residual chlorine that comes from the municipal water supply.

There is some data suggesting that not all urad beans harbor exactly the same bacteria which may impact the fermentation process, including the effects of washing or pre-treating the ingredients, and intermediate milestones during fermentation such as when one bacteria shuts down and another one becomes dominant.

Growing up in South India I have seen a lot of different methods to ferment. During colder months I have seen my mom using leftover overnight fermented rice (that's a very healthy refreshing breakfast dish) or just the fermented water to speed up fermentation. Sometimes the leftover batter. Considering the major fermenting microbes come from the lentils I'm not sure how fermented leftover rice helps. 

I use the whole black urad Dal as it has got lot of nutritive values. Also that was the older method of cooking because there were no dehulling machineries. What I have seen my grandma do - after over night soaking the whole lentil starts giving up skin, washing it thoroughly and removing part of the skin as it interferes with the texture of the final product, she starts grinding it using a grinder machine till it's super soft and fluffy. Because I can't afford a wet grinder in my small kitchen, I use blender and of course the downside is heat generated. Using ice water helps. I wash everything before soaking and use the soaked water to grind unlike my mom n grandma. They use fresh water.. I live in colder country and I can't have my batter for three days if I do that. Definitely the texture and taste of final product is different.

I have experimented with jasmine rice,  flattened rice (poha), idli rava, tapioca pearls (sabudhana). Everytime the difference is little as we consume idli and dosa with dominating flavour Rich sides like sambhar and chutney. I even tried making the idli/dosa premix powder, but as it involves roasting I lost hope during the process itself. And as expected it didn't ferment well even after two days. I have tried the store bought mixes that requires overnight fermentation, but in vain. That's when I was searching if sourdough Culture method will work for idli/dosa culture and landed here. I'll post here if I find success with sourdough method for culture maintenance. 

From my understanding of soil/ plant microbes and gut biome,  all batters function almost in a similar fashion.  I actually experimented by using sourdough starter from the fridge, just a few drops for regular idli/dosa batter as well as jalebi batter.  Just like sprouting seeds indoors in winter,  optimum temperature and water helps speed up the process.  Just like composting, 105-115f oven light temperature speeds up fermentation.  All seeds,  fruits and vegetables have vigorous amounts of diverse bacteria and fungi on them.  Fruits may have more fungi in some. You use them to auto populate as long as there's food available for them to grow.  Human hands have selective bacterial population that may affect the bacterial and yeast population on the long run,  examples bakers or moms making same food for decades daily such as baked goods or kimchi or pickles,  but l think it's not the deciding factor for regular fermentation.  I use garden organic green chili to store idli batter longer in the fridge with no fungus growth even after one month.  It's not the bacteria and fungi in air that mostly help with fermentation, but the ones hanging on the dal and grains.  That's why never eat raw flour.  Fungi give alcohols and bacteria acids.  Adding salt will alter the biology of batters but l use bakers 2% even for idli batter to rely on lactobacillus that thrives even in salty environment.  I never measure the salt,  use 1:2 or 1:3 dal: rice ratio to make more crispy dosa from the same idli batter.  More rice,  more crispy.  I never bear the mixed batter, never use hand,  still ferments heavily in 12 hours.  The last one hour makes the most bubbles. I use regular grinder that generates heat as heat is useful for my fermentation.  Even on very cold days,  mixing a few drops of my own sourdough starter ferments in 12 hours in oven with light on. Organic grains and lentils give the most diversity.  In USA, round up is used to dry the grain before harvesting. So regular grain may have remnants of round up that mess up grain biology and gut biology.