NGS (sometimes also referred to as GNS) refers to Neutral Grain Spirit. Neutral spirit, also known as neutral alcohol, rectified alcohol or ethyl alcohol is highly concentrated ethanol distilled until it reaches a min of 95% ABV (higher in Europe).
Think of NGS as a raw form of vodka.
NGS is an integral base for spirits like Gin as well as key to ‘cut’ liqueurs and make bitters. The really cheap vodkas are actually just NGS cut with water to bottling strength. It can be made from grains, grapes, molasses, potatoes, and many other agricultural origins (like apples or rice).
Neutral spirits are considered to be neutral in flavour and odour but contrary to popular belief this is not quite true. There are variations among the neutral spirits, some very noticeable to taste, with some having different mouthfeels and ways of “carrying” flavour. For example, wheat will be more creamy and slightly sweet, potato will be fuller mouthfeel, while rye has a warming bite on the finish.
The suppliers, the process, scale and agricultural origin of a Neutral Spirit all play a role in shaping the spirit, and while subtle, this is carried over into the flavour. Some suppliers even grade them in neutrality and while their inert nature is a talking point, it is more of a subjective preference and their suitability to match a recipe or a distiller’s intention which makes one better than another.