Consider three fundamental "ingredients".
Sugar is needed, specifically the kind of sugar that yeast can break down into alcohol, i.e. simple sugars such as Maltose and Fructose.
Obviously we need yeast, to supply alcohol from fermenting sugars.
Finally, we need flavour, which in the simplest beer is provided by more complex sugars and acids in the brew.
Sugar and most of the flavours in beer are provided by... [next slide]