Nitrogen in the beer (beer gas)
The main reason the above beers taste creamy is how they are carbonated. Instead of using regular CO2, these beers use nitrogen for “carbonation” (carbonation isn’t really the right word since you’re adding mostly nitrogen, not CO2). The beer gas used is not all nitrogen; it is a mixture of nitrogen and CO2. The presence of nitrogen gives the beer smaller bubbles, and will give a creamy mouthfeel.
The foam in a nitrogenated beer is much more stable than other beer heads. The reason is the atmosphere we breathe is mostly nitrogen, so there isn’t much driving force between the nitrogen in the beer and the nitrogen in the air. The faucet used to pour the beer perturbs the beer to produce the milky head.
A stout faucet has special parts to make the nitrogen/CO2 beer more frothy.
This isn’t the easiest method to change the mouthfeel of your beer. You will need a nitrogen system if you want to use beer gas. This includes a nitrogen (beer gas) tank and a nitrogen regulator. You cannot fill your CO2 tank with beer gas. Once you have the nitrogen setup, you “carbonate” your beer the same way you would carbonate with CO2.
You will also need a proper stout faucet. The faucet has a restrictor disk with small holes inserted in the path of the beer which causes the pressure to drop and release the beer gas. Then the faucet has a flow straightener. This helps direct the flow of the beer into a single direction after passing through the holes.
Most places which sell CO2 will also sell beer gas. If you are having troubles locating beer gas, you might check with your local homebrew store or homebrew club. They should be able to help you find the beer gas.
Higher Temp Mash
You can get a thicker mouthfeel with more unfermentable sugars in your beer. These unfermentable sugars increase the viscosity of the beer, making it feel thicker. So how do you get more unfermentable sugars in your wort?
If you mash your grains at a higher temperature, you will get more sugars the yeast can’t eat. The enzymes that break down the starches work at specific temperatures. Some only work at lower temperatures. The alpha-amylase enzyme works best at temperatures 150F-158F (60C -70C), but the beta-amylase enzyme is denatured at 150F. Mashing your grain at 158 F will produce a more dextrinous wort.
You can’t do this in an extract brew because you don’t control the temperature. You can add malto-dextrin however, which will give the beer a thicker feel.
Oats and Flaked Barley
Oats and flaked barley add beta glucans to your wort, which are mostly unfermentable by yeast. This will add viscosity to the final brew. The more unfermentables in your beer will make the beer thicker, but oats or flaked barley will give the beer more of a silky feeling in your mouth.
These cannot be used in an extract brew because both have starches which need to be converted. If you are an extract brewer who wants to use oats or flaked barley, you’ll need to look into partial mashing.
Lactose
Lactose is a semi-sweet sugar which is often found in milk. Lactose is not fermentable by yeast, and it will give your beer a milky mouthfeel. Lactose is added to Milk Stouts to increase the body of the beer, and give it a creamy mouth feel.
In the UK, these beers are called Lacto Stout or Sweet Stout. The USA doesn’t have the same laws regarding labeling, so they are usually called Milk Stouts. A good example of a Milk Stout is Left Hand Brewery’s Milk Stout.
Be careful to let your friends know the beer contains lactose, since some people are lactose intolerant. According to the National Digestive Diseases Information Clearinghouse, some 30 million to 50 million Americans are lactose intolerant, including up to 75 percent of African Americans and American Indians and 90 percent of Asian Americans.
Lower carbonation
Lower carbonated beers also will feel “thicker” in your mouth. You’ll notice this in oak aged ales or other British ales. The beer won’t taste milky, but the lack of carbonation will give the beer more body.
from Fermentarium