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|Dry urad beans|
Vigna mungo, known as Urad Dal, black gram, black lentil (not to be confused with the much smaller true black lentil (Lens culinaris)), white lentil, black matpe bean, is a bean grown in the Indian subcontinent. It, along with the mung bean, was placed in Phaseolus, but has since been transferred to Vigna. At one time it was considered to belong to the same species as the mung bean. The product sold as "black lentil" is usually the whole urad bean or urad dal. The product sold as "white lentil" is the same lentil with the black skin removed.
Black gram originated in India, where it has been in cultivation from ancient times and is one of the most highly prized pulses of India and Pakistan. The coastal Andhra region in Andhra Pradesh is famous for black gram after paddy. The Guntur District ranks first in Andhra Pradesh for the production of black gram. Black gram has also been introduced to other tropical areas mainly by Indian immigrants.
It is an erect, suberect or trailing, densely hairy, annual herb. The tap root produces a branched root system with smooth, rounded nodules. The pods are narrow, cylindrical and up to six cm long.
It is largely used to make dal from the whole or split, dehusked seeds. The bean is boiled and eaten whole or, after splitting, made into dal; prepared like this it has an unusual mucilaginous texture. It is also extensively used in South Indian culinary preparations. Urad Dal is one of the key ingredient in making the Idli-Dosa batter, where one part of Urad Dal is mixed with Three or Four parts of Idli Rice to make the batter. Also the dough for Medu Vada or Udid Vada is made from soaked batter and deep fried in cooking oil. The dough is also used in making Paapad, notably the South Indian version known as Appalam and Papadum, in which white lentils are usually used.
It is nutritious and is recommended for diabetics, as are other pulses. It is very popular in the Punjabi cuisine, as an ingredient of dal makhani. In Bengal it is made as a preparation called Biulir Dal. In Rajasthan, It is used to prepare dal which is especially consumed with "Bati".
It has been historically used as cementing agent along with other ingredients in the construction of several historic buildings.
Use in medieval crucible construction
In medieval times, this bean was used in making crucibles impermeable. 
In Hindi it is variously called urad, urad dal, udad dal, urd bean, urd, urid, maash (in Nepali), or උඳු (Sinhala), đậu muồng ăn (Vietnamese). It is known as uzhunu (ഉഴുന്ന്) in Malayalam, minumulu (మినుములు) in Telugu, uddina bele (ಉದ್ದಿನ ಬೇಳೆ) in Kannada, urdu bele in Tulu, ulunthu(உளுந்து) in Tamil, adad (અળદ) in Gujarati and biri dali in Oriya.
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- Vijaya J. Deshpande. "Musavijnana or the ancient science of crucibles". Indian National Science Academy.
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