The Indonesian mortar is made from a hard basalt stone. Although the cobek has a smooth appearance the stone is rough enough to crush and break through the typical sambal ingredients like chiles, garlic, peanuts, coconut and even lemon grass.
The traditional mortar and pestle can also be found made of palm wood. While the wood version is very attractive it is not quite the efficient grinding tool. Some cooks like using the palm wood pestle with the stone mortar.
A new cobek and ulek ulek should be prepared before it is used for the first time. Always wash both pieces well in warm soapy (unscented) water.
One source suggests wiping a new mortar out with a stale slice of bread or using grated coconut. While this process will remove any loose stones in the mortar we suggest a method that takes a bit longer but prepares the mortar more thoroughly.
Another technique is to season the mortar with a paste made from kosher salt and raw garlic. Place 3 - 4 large, peeled garlic cloves in the center of the bowl with about 2 tablespoons of kosher salt. Use the pestle to mash the ingredients into the surface of the bowl. Allow the mixture to sit in the mortar for a couple of hours or over night. Then scrape out the mixture and rinse the mortar and pestle with warm water and allow to air dry.
Both fresh and dry chiles are used in making sambals. Whole fresh and dried chiles need to be stemmed, cleaned and seeds removed before use. Smaller chiles such as pequin don't require cleaning. Dried chiles are typically re-hydrated before use and fresh chiles may or may not be precooked.
Garlic, shallots and other soft ingredient should simply be peeled. Some larger ingredients such as tomatoes should be cut into medium sized pieces
Some recipes may suggest grinding ingredients in a specific order to facilitate even grinding. Make sure to refer to your recipe. Salt may be added in intervals to help break down coarse foods.
Ingredients are crushed together using a firm but gentle up and down motion. This crushing extracts the most flavor from the ingredients and gives the sambal the traditional texture. It takes about 3 to 4 minutes of "vigorous work" to create a paste of the proper consistency.
These mortars tend to be very hard to find in the U.S. We do sell them online at GourmetSleuth.com. Because this product is difficult to obtain we may not always have them available.