Spikelets are arranged in triplets which alternate along the rachis.
In wild barley (and other Old World species of Hordeum), only the central spikelet is fertile, while the other two are reduced.
This condition is retained in certain cultivars known as two-row barleys.
A pair of mutations (one dominant, the other recessive) result in fertile lateral spikelets to produce six-row barleys.
Recent genetic studies have revealed that a mutation in one gene, vrs1, is responsible for the transition from two-row to six-row barley.

Two-row barley has a lower protein content than six-row barley, thus a more fermentable sugar content.
High-protein barley is best suited for animal feed.
Malting barley is usually lower protein
("low grain nitrogen", usually produced without a late fertilizer application) which shows more uniform germination, needs shorter steeping, and has less protein in the extract that can make beer cloudy.
Two-row barley is traditionally used in English ale-style beers, with two-row malted summer barley being preferred for traditional German beers.

Amylase-rich six-row barley is common in some American lager-style beers, especially when adjuncts such as corn and rice are used.
Spikelets are arranged in triplets which alternate along the rachis. In wild barley (and other Old World species of Hordeum), only the central spikelet is fertile, while the other two are reduced. This condition is retained in certain cultivars known as two-row barleys. A pair of mutations (one dominant, the other recessive) result in fertile lateral spikelets to produce six-row barleys. Recent genetic studies have revealed that a mutation in one gene, vrs1, is responsible for the transition from two-row to six-row barley.
Two-row barley has a lower protein content than six-row barley, thus a more fermentable sugar content. High-protein barley is best suited for animal feed. Malting barley is usually lower protein
("low grain nitrogen", usually produced without a late fertilizer application) which shows more uniform germination, needs shorter steeping, and has less protein in the extract that can make beer cloudy. Two-row barley is traditionally used in English ale-style beers, with two-row malted summer barley being preferred for traditional German beers.
Amylase-rich six-row barley is common in some American lager-style beers, especially when adjuncts such as corn and rice are used.
Barley