Spoonful is approximately 20ml, but the recipe author is saying the exact measurement is not important and that this is a particular lever to adjust for taste.

Spoonful is approximately 20ml, but the recipe author is saying the exact measurement is not important and that this is a particular lever to adjust for taste. (A spoonful of sugar means that some people will prefer this sweeter and some more savory, and that you should use judgement based on you or your audience.)