The simplest approach to make a higher alcohol beer is to add more sugar during fermentation. During beer's fermentation process, yeast eats the sugar made from malted grain and then converts it into alcohol and CO2. If there is more available sugar, the yeast has more food to eat, which produces more alcohol.
What are the steps in making beer? The beer brewing process involves malting, milling, mashing, extract separation, hop addition and boiling, removal of hops and precipitates, cooling and aeration, fermentation, separation of yeast from young beer, aging, and maturing.