I learned about soapberries from a Facebook group called Oklahoma Wildcrafting. Another thing I have learned by keeping up with this group is how to use native sumac seeds to make a kind of spice that has a tangy lemony taste.
There are many varieties of sumac, including Poison Sumac. You don't want to eat that! In general, the varieties that have red berries are edible. The following is a picture of the typical native sumac shrub that grows along the roadsides and in the fields here in Oklahoma.
The spice is made from the seeds that make up the red clusters, like you see above. Here's one of them.
Here's how to make the spice. First, remove the seeds from the stem. This can be quickly accomplished by rubbing the bunch between the palms of your hands over a piece of newspaper. Then, pick through the seeds and remove any bits of stem and other debris.
Next, put the seeds in a mortar and grind them until the red coating comes off.
It should look something like this.
Pour the mixture into a sifter and shake the bits of red seed coating into a dish. It is the seed coating that you want for the spice, not the inner seed.
At this point, a lot of the seed coating may be too big to go through the sifter. So, you can pour it back in the mortar, regrind and re-sifted it again. Some of the seed coating may stick to the inside of the mortar. You don't want to waste it, so use a pastry brush to brush this out.
Finally, pour the spice into an empty spice bottle and label it.
I sprinkled the spice on sugar cookies before baking. This gave them a delicate lemony taste that was delightful.
I found many other recipes for using this spice on the internet. It appears to be used a lot in Middle Eastern cuisine.
If you are interested in making your own sumac spice, the following Eat the Weeds website is very informative and tells how to make a type of "lemonade" from the berries.