What is peat primarily composed of?

Peat is primarily composed of partly decayed vegetation, which accumulates in waterlogged conditions over thousands of years. This organic matter includes plant material such as mosses, especially sphagnum moss, along with other types of plant life, which decay at a slower rate due to the anaerobic conditions found in bogs and wetlands. This unique accumulation process gives peat its distinctive characteristics and contributes to its use as a flavoring agent in some whiskies, imparting a smoky flavor when burned during the malting process.

The other choices refer to different materials or processes: wood-based products are derived from trees, not primarily from decayed vegetation; processed grains pertain to the cereal grains that are fermented in the production of spirits; and burnt barley could refer specifically to a malt preparation but does not define the composition of peat itself. This distinction is crucial for understanding how different components contribute to the spirit-making process.