How to make the best Gundruk
Gundruk is a fermented leafy green vegetable and a popular food in Nepal. Gundruk is obtained by fermenting and drying leafy vegetables (saag) to produce a sour brownish black product. It can be served as a side dish, used as an appetizer or can be made into a soup.
Gundruk is an important source of minerals, particularly during the off-season when the diet consists of mostly starchy tubers and maize, which tend to be low in minerals. 
In the months of October and November, during the harvest of the first broad mustard, radish, spinach and cauliflower leaves, large quantities of leaves accumulate - much more than can be consumed fresh. 
Image source: Gaurav Dhwaj Khadka
These leaves are allowed to wilt for one or two days and then shredded with a knife or sickle. The shredded leaves are tightly packed in an earthenware pot, and warm water (at about 30 °C) is added to cover all the leaves. The pot is then kept in a warm place. After around a week, a mild acidic taste indicates the end of fermentation and the Gundruk is removed and dried in the sun. This process is similar to sauerkraut or kimchi production except that no salt is added to the shredded leaves before the start of Gundruk fermentation. The ambient temperature at the time of fermentation is about 18°C.
So what are the optimum conditions for Gundruk?
Well it depends on your taste. However, according to Shrestha et al. (2012), Gundruk prepared in 24±1 ̊C reaches its optimum value of acidity on the 9th day of fermentation and among all the fermentation containers used, the Gundruk prepared in glass container was found to have the best quality. 
1. Battcock, Mike; Azam-Ali, Sue (1998). Fermented fruits and vegetables : A global perspective. Rome: Food and Agriculture Organization of the United Nations. p. 66.
2. Practical Action Nepal, Gundruk (Pickled Leafy Vegetable)
3. Shrestha, Roshan; Bhattarai, Rewati Raman; Katawal, Surendra Bahadur. Effect of different fermentation containers on the quality of gundruk >