Particulates can mess up your reading, in my experience, which is measuring soil pH. I’ve never bothered with wort
Take a liquid sample from the well stirred mash. It doesn't have to be strained or anything, but try to get liquid and avoid solids.
I do strain a little mash through a cheesecloth prior to taking a reading. Even if it isn't necessary, it makes me feel better not having any particles of grain in the liquid.
