E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Maiden Assize (A).
One in which there is no person to be brought to trial. We have also the expressions maiden tree, one never lopped; maiden fortress, one never taken; maiden speech; etc. In a maiden assize, the sheriff of the county presents the judge with a pair of white gloves. White gloves symbolise innocence. Maiden primarily means unspotted, unpolluted, innocent; thus Hubert says to the king