I'd always wondered how they made wooden barrels to a specific capacity. It seems that the simple answer is: they didn't.
"THE SIZE OF BREWERS CASKS.
IMPORTANT RAINTON APPEAL.
In the King's Bench Division yesterday, the case of the North-Eastern Breweries v. Gibson came before the Lord Chief Justice and Justices Wills and Kennedy, on appeal from a decision of the Justices of Durham, on a case stated by the Justices for the opinion of the High Court.
The facts of the case are that Robert Gibson is licensed victualler, and a tenant under the appellants of the Lord Seaham public-house, at West Rainton. In October last Gibson ordered one kilderkin mild ale. and received from the appellants cask of ale which held only gallons 1 quart and 1 pint, the respondent also proved that had in his possession eleven other casks, purporting to kilderkins of gallons each, and that seven of such casks were deficient in holding capacity; of the remainder one held exactly 18 gallons, and three slightly more than that quantity. On behalf the appellants it was proved that the process of coopering casks had the effect of diminishing their holding capacity, and that it was usual to send with casks an invoice, which was stamped with the words: "Our casks are vessels to carry beer, not measures, but care is taken that they contain not less than their reputed quantities." The invoice left with the respondent in this case did not bear the words referred to.
The Justices stated that after careful consideration of all the evidence, they found as facts (1) that a kilderkin a cask of sufficient capacity to hold 18 gallons. (2) that the cask only held 17 gallons 1 quart and 1 pint, (3) that the cask had been supplied to the respondent by the appellants in the usual course of business and with their knowledge, (4)that the appellants were aware that the process of coopering casks had the effect of diminishing the holding capacity of such casks. They therefore convicted the appellants of the offence charged, and inflicted a penalty of £5 and £2 0s 6d costs.
The Lord Chief Justice, giving the judgment the Court, held that the Justices were right in their findings, and dismissed the appeal with costs."
Sunderland Daily Echo and Shipping Gazette - Friday 06 May 1904, page 6.
The offending cask was 5 pints short of 18 gallons. That's 5 pints out of 144 in total. Or about 3.5% short. Not a huge shortfall, if you look at it in percentage terms. And not as much as the 5% short that landlords are allowed to pull your pint today.
I've seen a similar disclaimer on some old beer labels, saying that they are vessels for transporing beer, not measures. It always implied to me that the bastards were deliberately using under-sized bottles. But then again I'm a cynical bastard.
I remember my brother telling me about how Home Ales invoiced for beer. He knew it from being the accountant for some of their publicans. They's weigh the cask before and after filling so they could calculate exactly how much beer was inside it. They charged for the actual contents rather than the nominal capacity of the cask. It seems a very fair system to me.