Understanding the difference between porter and stout is, at best, complicated because there are no legal definitions for each type of beer. Generally, the main differences of porter vs. stout comes down to the treatment of the barley used to make the beer, the resulting flavor profiles, and what the brewer decides to call it.
Porter vs. Stout Similarities and Differences
There's a lot of crossover in the categories of porter and stout because the two beers are similar. This is because they have shared ancestry. In the timeline of brewing history, porter came before stout. In fact, stouts are direct descendants of porters, which is why some people are confused about the differences. The earliest stouts were called "stout porters" because they resulted from tinkering with traditional porter recipes to create a more robust, more alcoholic brown ale. In other words, stouts started out as porters with additional ingredients or different processes added and higher alcohol by volume (ABV), but they became their own category as they grew in popularity. It's important to note that while the general similarities and differences are listed below, there are no legal requirements for naming these two dark beers, so ultimately it's up to the brewer as to what to call their beer.
Porter and Stout Are Both Dark Beers
Both porter and stout are deep brown to almost black colored beers. They are similar in color to a dark brewed coffee, and with the perfect pour, they have a creamy, dense, foamy head. In general, stouts tend to have a slightly darker color than a porter.
Stout and Porter Brewers Use Barley Differently
Generally, brewers use malted barley in porters and roasted, unmalted barley in stouts. This affects the body and flavor of the resulting brew and is probably the primary distinction between the two types of beer.
They Have Slightly Different Taste Profiles
Porters tend to be more chocolately; stouts are often more coffee-like in flavor. However, these are generalities, and there's a great deal of crossover in flavors between the two. Generally, porters may have subtler flavors than stouts due to the differences in how the barley is processed. While both have bitter and creamy flavors, porters tend to have deeply roasted, malty notes while stouts have more intense, almost burned notes. Stouts also tend to be more strongly bitter than porters, but they also typically have more creamy notes to temper the bitterness. Generally, a porter has smoother, subtler flavors than a stout, while stouts tend to be more in-your-face with their flavor profiles. Porters tend to be smoother; stouts tend to be less subtle. However, all of these things are a matter of degree and ultimately depend on what the brewer intends to create with his or her porter or stout.
Stouts Tend to Be Fuller Bodied Than Porters
As a generalization, a stout is thicker and more viscous than a porter, which gives it a more full-bodied mouthfeel. However, as with everything else porter and stout, this is a generalization, and it's likely you'll find some beers called porters that are fuller bodied than some beers called stouts.
Stouts Are Likely to Have More Alcohol Than Porters
Since there's no legal requirement for naming either a porter or a stout, there's no hard-and-fast rule about which is stronger. Historically, stouts (stout porters) were stronger than their predecessors; however, in today's brewing industry, that isn't always the case. Both are strong brown beers with a range of about 4% alcohol by volume (ABV) to as high as 12% ABV. Ultimately, the final ABV of the ale depends on the brewer and the subcategory of porter or stout. When choosing a porter and a stout made by the same brewer, chances are the stout will be higher in alcohol. However, when comparing one brewer's porter to another's stout, these conventions will likely go out the window.
Stouts May Be Sweeter
Because of the increased bitterness in a stout, brewers may balance this by adding more sweetness. Therefore, many people find stouts to be sweeter than porters, but as with everything else, this isn't always the case.
Both Are Large Categories With Smaller Subcategories
Porters and stouts are each a category of beer; underneath each are many subcategories. It is often in these subcategories where the biggest differences between porter and stout reveal themselves. For example, a Baltic porter is stronger and more full-bodied than many stouts, while an oatmeal stout may be weaker and lighter than a traditional porter.
Porters and Stouts Can Be Either Ales or Lagers
Again, this is a generalization; however, most porters and stouts are ales produced from top-fermented yeast; however, some porters and stouts are lagers that use bottom-fermented yeast.
Both Pair Well With Food
Both porter and stout are delicious beers to pair with foods. Their toasty flavors hold up well to rich foods like steak and burgers, so you can't go wrong ordering either with a meal.
Difference Between Porter and Stout Depends on the Brewer
In general, the difference between these two beers is what the brewer decides to call it. With significant similarities in style, the most distinct difference you'll generally find between the two is the use of malted barley versus roasted barley, but ultimately it comes down to what name the brewer decides to give it.