Tongba actually is the vessel which holds the fermented alcoholic beverage known as Jaand. Jaand is the cooked millet is cooled and mixed with murcha (which is a source of molds, bacteria and yeast). It is consumed in a unique way: the fermented millet is put in a container traditionally called a Tongba, and boiled water is poured in it to the brim. It is then left undisturbed for about five minutes.
You can make tongba all year round, at every elevation handy for the Himalayas.
And, because the fermentation happens in the grains and the water is added later, it’s a lot more portable than your typical beer.