1) Barm is a regional word for yeast, the froth of fermenting malt liquors which can be used as a leavening agent. Halliwell defined 'barme-cloth' as an apron, presumably one used by the workmen:
1304 In grossa tela pro barmeclathes et pro caseo, Bolton Priory
1423 j barmecloth de rubeo panno auri, York. The word survived in regional use when ‘yeast’ became more popular generally: c.1534 10 barm tobbes, Bridlington
1632 for barme 4s, Thornhill
c.1760 yeast, in some places called barme, Wakefield.