Buckwheat is a pseudocereal, and not a grass. In spite of the name it is not related to wheat and is more closely related to sorrel and rhubarb. The name derives from Dutch boecweite (“beech-wheat”), perhaps because the seeds resemble those of the beech tree.
The plant originated in China, and with domestication spread through Asia and Europe. Buckwheat is naturally gluten free and features in a number of Asian and European cuisines (e.g. soba noodles, kasha, and crepes).
Use in Beer
Although buckwheat is not frequently used as a base malt for gluten free brewing, it does have some useful qualities for brewing. The high protein and low lipid content of buckwheat means that it is a positive contributor to foam production and retention. The higher beta glucan content is a double-edged sword for brewing: although this can aid in providing more viscosity and body, that gumminess can be a real problem during the mash, causing issues with slow filtration and stuck mashes. A beta glucan rest during the initial mash can help overcome this problem, as can exogenous beta glucanase enzymes.
Buckwheat is a prime contributor of caprylic acid, a precursor to ethyl caprylate. When synthesized from caprylic acid by Brettanomyces, ethyl caprylate can produce sweet, fruity, pineapple esters. 
- Optimisation of a Mashing Program for 100% Malted Buckwheat
- Processing of a Top Fermented Beer Brewed from 100% Buckwheat Malt with Sensory and Analytical Characterisation
- Behaviour of Malted Cereals and Pseudo‐Cereals for Gluten‐Free Beer Production
- Malting buckwheat - Brewing Beer the Hard Way blog, Francois Dyment
- Milk the Funk FB group thread on brewing with malted and raw buckwheat (Must be a MTF member to view)