The craft or process of making barrels; the trade or skill involved in barrel construction.
From barrel plus making (the gerund of make), forming a compound noun describing the activity. This is a transparent formation, though coopers would have called their craft 'cooperage.'
Barrelmaking involved seven different specialized skills—choosing the right wood type, seasoning it, splitting it perfectly, bending it with heat and water, fitting hoops, adding a lining, and sealing it. Medieval guilds carefully guarded these secrets.
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