An old name for spelt, which is identical with beer barley or beer corn, or German wheat, much grown in Scotland, Germany, Switzerland, &c., and used for malting.
From The Baker’s ABC by John Kirkland, formerly Head Teacher of National School of Baking, published 1927 by Gresham
The Vintage Cookbook Trials 
Oh no it isn’t! Spelt (as we currently use the word) is only very very rarely used to make beer, even in 1927…
Oxford Companion to Beer says the very earliest beer brewed by the Sumerians (10,000 years ago) probably used spelt, but barley has been the beer grain of choice for at least a couple of millennia…
My Chambers dictionary says zea is another name for maize; but ‘corn’ can be used to mean any cereal crop, not specifically maize/sweetcorn.