Stouts and Porters

Why do dry stouts have low ABV?

Dry stouts, like Guinness (or NC’s Fonta Flora - Irish Table), typically have low alcohol content (around 4-5% ABV) because they utilize unmalted roasted barley which doesn't contribute as much fermentable sugars to the brewing process as malted barley. The “dry” finish (lower sweetness) results from a moderate addition of hops – balancing the malt character with hop bitterness.

Less-dry stouts include milk, oatmeal and imperial styles. Examples from NC Brewers include:

• Milk Stout – Duck-Rabbit - Milk Stout

• Oatmeal Stout – Fullsteam - MB Stout

• Imperial Stout – Asheville Brewing – Carolina Mountain Monster

The less-dry – or sweeter – taste of these stouts is a result of using a combination of more malted barley and other sources of sugar such as milk (non-fermentable lactose) or oatmeal (fermentable).

Porters vs. Stouts

There is very little difference between a stout and a porter. Stouts use unmalted roasted barley while Porters use malted roasted barley. They both have the rich, dark color of roasted barley, but stouts are drier while porters are a little sweeter with more body.

Here is an excellent source for more information about Stouts and Porters.