When you read about beer, the water factor often isn't discussed, because it's a given. Everyone knows water is involved, it's clearly the largest factor. That said, it's stupid to dismiss it's importance. The effect a soft water vs hard water profile will have on the same recipe brewed exactly the same way, can be enormous. Mineral profile as well. This fact contributes to why breweries will sometimes release their recipes to the homebrew crowd. They know that without the specific water conditions being matched, it'll be virtually impossible to duplicate. Let's not forget temperature of the water or municipal additions like chlorine or flouride and their affect also make duplication of beers that much more difficult.

aka. starches, or sugars extracted from a wide variety of sources (usually grains mildly roasted or kilned to varying degrees) provide the base to almost every beer. Two beers that taste completely different can often have the exact same base malt, even to the same proportion of the whole recipe. This ingredient type mostly affects color and potential alcohol concentration. It also affects aroma, flavor, and mouthfeel but to a lesser extent. There are often other malts in beer recipes. These are known as 'specialty malts' & will typically be very small percentage of the whole, but help to impart dramatic color shifts and flavor to a beer. It's worth noting, while very few malts contribute to the bitterness of the beer, it is possible, especially in some dark roasted or smoked malts.

Historically, hops were added to act as a preservative, as the drink was used on ships attempting to sail long distances. The antibacterial properties of lupulin in hops did this quite effectively. 

Nowadays we appreciate hops in beer for it's 3 other contributions: bitterness, flavor & aroma. Sometimes all 3 aspects can be done with a single hop varietal, and at other times, it's done with an assortment of hop varietals.

Perhaps the best way to think about hop ratios and their impact is in terms of balance to a beer's flavor profile. Fewer hops generally produce more sweet flavors, more hops - more bitterness. Brewers choose their hops carefully to find just the right balance they seek for the style they're brewing. In addition to bitterness for sake of balance, hops will also have unique flavor and aroma characteristics. The hops chosen will cause certain flavors or aromas that are often compared to pine, citrus, fruit, herbs, floral, grass, etc. 

Everyone's favorite ingredient even though they don't know it. Yeast, the single-celled organism that is responsible for converting all the sugars produced in the mash called wort (pronounced wert) to alcohol during fermentation.

Yeast is often thought of in 3 brewing classifications: 'Top' ferment for ales at higher temperatures, 'Bottom' ferment for lagers at lower temperatures, and 'Spontaneous' ferment for wild or sour beers which have a greater range for ideal fermentation temperatures.