|Idli is India's oldest most sophisticated dish.
Traditionally, Urad and Rice are soaked for a time period. Then these two items are ground together and left to ferment overnight to make batter for various South Indian dishes. In United states, fermentation is becoming a problem. The water is chlorinated, table salt is iodized and both these are not friends of wild yeast. The homes have central air-conditioning many with hypo-allergenic filters, reducing the supply of the "wild yeast". Guide for Idli Dosa Batter .
The fermentation is caused by air-born wild yeast. Urad and Fenugreek seeds draw the wild yeast from air. Do NOT over-wash Urad Dal or Fenugreek seeds, as it will wash away the collected wild yeast.
The Chlorine in the water can destroy the wild yeast. Use spring water, boiled or filtered tap water to avoid Chlorine.
In United States common table salt is iodized. The iodine can destroy the wild yeast. Use non-iodized salt such as 'Kosher salt'.
The fermentation can be retarded by Yogurt, Baking yeast, Baking soda or Baking powder. Only after fermentation is complete , you may add Yogurt or baking agents as needed.
The best ambient temperature for incubation is 86º F to 90º F. If the temperature is below 86º F, it will take longer to achieve acceptable level of fermentation. If the temperature is higher than 90º F, the batter may become sour. Acceptable level of fermentation is when the batter has reached 250% in volume (Two and a half time the original volume).
Idli is supposed to be white, plump and soft. All these three aspects depend on rice.
Of course in the olden days, there was NO parboiled/converted rice. After the husk was removed, the resulting brown rice was used to make Idli. The rice was boiled and then later ground. However, now a days Parboiled/Converted rice is used. Parboiled rice is pre-processed, reducing the time required to pre-soak before grinding by about 4 hours on average. Parboiled rice also has gelatinized starch which gives added texture.
There are two types of starch in rice; Amylose and Amylopectin. Long grain rice has 22 percent Amylose and 78 Amylopectin, while medium/short grain rice has 18 percent Amylose and 82 percent Amylopectin. Note corn starch is 100% Amylose. You need over 80% Amylopectin to make Idli soft and plump. Use short to medium grain size rice. If you don't have access to Idli rice, you may use Arborio Rice (or any other Italian rice suitable to make Risotto) or even Mochi Rice (Japan) or sweet/ waxy American Rice.
You cannot use rice flour as it will render poor texture. However, you may be able to use Cream-Of-Rice. Cream of rice is coarsely ground rice. There is one problem with cream-of rice. The manufacturers do not disclose the type of rice grain used to make cream of rice, so the percentage of Amylopectin might not be acceptable. You might have to experiment from brand to brand.
You can always use whole Urad with the black skin. The only problem is cosmetics due to black fragments left after it is ground. Decorticated whole Urad is preferred. Decortications process involves introducing moisture to remove the skin. The split Urad has a problem. The pulse is split mechanically that generates heat and destroys much of the wild yeast. To compensate for this, you may add Fenugreek seeds to aid in fermentation.
Urad Dal Flour
You can use Urad Dal flour. The only problem you have is that some of the wild yeast is destroyed by heat during milling process. To compensate for this, you may add Fenugreek seeds to aid in fermentation.
Type of a pan
In the olden days, professionals used earthen (Terracotta) pans about 5" deep and 16" diameter.
Use stainless steel pan or plastic pan of large diameter. A 12" diameter pan will have more than twice the surface area of a 8" pan to catch "wild yeast". If you don't have large diameter pan, divide the mixture in to two separate pans. Two 8" pans will be same as one 12" pan. The depth of the pan should be such that it can hold 4 times the original amount of Rice & Urad Dal.
Why do we use Fenugreek Seeds?
Fenugreek seeds draw the same type of wild yeast as the Urad Dal. This just adds to draw more yeast. In traditional method, the seeds are put in the Rice pan so that both the pans (Urad Dal, as well as the Rice) will draw wild yeast.
Can I artificially introduce "Wild Yeast"?
You can harvest wild yeast from fresh fruits that have not been cleaned commercially. You will notice a white powdery substance stuck on the apples, plums or red grapes. This is wild yeast. You can wash the fruits in spring water. Now the spring water has the yeast. Use this water to make batter. You can also try tamed yeast to make wine-vinegar.
How Dosa Batter differs from Idli Batter?
1. The Dosa batter is thinner than than the Idli batter. This consistency is required to make the crepe.
2. There is less Amylopectin in Dosa than Idli. The Dosa crepe has to be crusty and crisp, while the Idli is soft and fluffy. You can just add water and thin Idli batter to make crispy Dosa.
You may add Dahi, (Yogurt) to make Idli batter. The lactic acid and the butterfat in the Yogurt, tenderizes the gluten, making Idli soft.