Crabapple Verjuice

Food in England, Dorothy Hartley, p. 422

Ms. Hartley claims crab apples make the best quality apple verjuice.

? lbs crab apples, when their kernels have turned black

Tools required - wooden trough, wooden mallets, coarse weave bag or cheesecloth, a carboy or wooden cask the size of a hogshead (typically between 200 and 300L).

1. When the kernels have turned black, harvest the crab apples and keep them in their baskets to 'sweat' for 7-10 days ('sweating' in this context is to let the apples sit in a shaded warm odour free place where they can finish developing their sugars and flavour profiles. They're done 'sweating' when a squeeze leave finger impressions in the fruit).
2. In non-reactive troughs (wooden is choice), beat and crush with wooden mallets called beetles to release the juices.
3. (This bit I'm uncertain. Dorothy transcribes 'Make a bagge or coarse hair-cloth and fill it with crabbes, and presse and run the liquor into Hogsheads.' If I were to extrapolate, it sounds like something like the 'cheese' made from straw in the Edwardian Farm (I think it was). It may be that the community apply press will do the job just fine without any fuss).
4. (Can I complete the fermentation as I would for wine-making, in a carboy etc?)