When fermenting with Mr Beer plastic Keg or upright Carboy, and I want to add a fruit flavor. Is the best way to add the flavor to add actual fruit or use the essence of the fruit that I want to use. Any help is very much appreciated.
Given that you would like to add fruit flavor to the same vessel that you plan to use for serving, adding actual fruit might become problematic. If you were attempting to add fruit flavor in a fermentation vessel, your options would be more numerous, but in your case, you might consider using a fruit flavor extract. Brewing supply stores carry many fruit options (strawberry, cherry, apricot, blueberry, peach, raspberry, etc). A note of caution, though. Even though these are often billed as "natural flavors", they can come across as "cough syrup" in some cases. Consider an experiment using a measured dilution of the flavoring and an eye dropper with small samples of your beer at various numbers of drops. You can identify the least detectable level of flavor and possibly the "overpowering" level of flavor, then calculate how much flavoring you'd need to add to get to a pleasing level of fruitiness.