The simplest way to describe "Rujak" is fruit salad. The fruit in this particular picture is actually a root known as "Bengkuang", I grew up knowing it as "Besusu" which is the Javanese word for it. I don't know the English word for Bengkuang but the Latin name is "Pachyrizhus Erosus" It ican be eaten peeled as is and is sweet & crunchy or cooked in a stir fry with vegetables and mushrooms. I sometimes put it in spring rolls to give it an added hint of sweetness and oddly with every bite, the crunchiness remains intact. The extract of Bengkuang is found in many beauty products and usually sold as a facial mask. And in a more holistic way it is used to treat boils. But I won't get into that in detail since I am writing about food. haha
Rujak is popular throughout the South East Asian region particularly among pregnant women. Where in the West oftentimes women crave for pickles - Rujak is our craving must have food. This particular picture is the Central Java style Rujak known more commonly as "Lotis". The ingredients of the sauce is made of chilli, shrimp paste, salt, tamarind that has been soaked in a little warm water and pitted as well as coconut palm sugar that comes in the form of a block. This is all ground in a mortar until it becomes a thick paste and dipped with whatever fruit you have around the house - usually; pineapple, young mango, young pepaya etc. If these type of fruits are not readily available where you are , then you can replace it with apples, pears and pomelo.
In Malaysia and Singapore it is known as "Rojak", the consistency of the sauce is much more diluted. In Jakarta, the sauce is grounded with peanuts as well and in Bali the sauce is also very watery and made with vinegar. Another version of Rujak that is popular here is known as "Rujak Bebeg", it's basically the same ingredients in diluted form and fruit is grated and mixed in the sauce. But I'm biased when it comes to rujak because my first introduction to it was the Java style lotis so nothing else compares.
Vendors sell rujak along the streets in the heat of the afternoon, it's actually a perfect snack to cool you off. However, I've never bought rujak in this manner because the peeled fruit is exposed in the sun even though there are blocks of ice to cool it and sometimes there are even flies swarming around. So, I'll pass for it's so easy to make and usually I make a lot of the sauce because it keeps well in the fridge for quite some time to enjoy on another hot afternoon...