When we make homemade Coffee Ice Cream, using instant coffee dissolved in hotwater, we always have icicles form. Is this avoidable?
With respect to the coffee: Rather than dissolving the coffee granules in water, try dissolving them directly in the cream.
There are a couple of reasons icicles form, but the most frequent culprit in my experience is ice cream having been allowed to come to too high a temperature at some point in the process, as early as when you begin churning.
When the ice cream gets to its melting point, the water molecules can start to separate from the cream mixture and, when re-freezing without another churn, the water will freeze into ice without reincorporating back into the cream, so you will have that off-putting icy texture.
Make sure your ice cream is constantly cold and that if you let it out to soften before scooping, you immediately return it to the freezer before it starts to completely liquefy.