Headspace is the real cost
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The legal position is permissive
Fill a 946 millilitre bottle to 750 and label it 750. Nothing in the standards of fill prevents it.
And the product suffers
A fermented beverage with a large headspace oxidizes faster, because there is more oxygen in contact with it and more surface for exchange.
Cider is particularly exposed
It browns and loses its fresh fruit character with oxygen, which is the first thing a drinker notices and the hardest thing to recover.
Mead has sugar and time on its side
A sweet mead at higher alcohol is more robust, and it is often aged deliberately. The same headspace is less punishing.
Then there is the presentation problem
A bottle visibly short of full reads as underfilled whatever the label says. Nine of our fourteen containers are clear glass, so it shows.
Which is why the standards and the bottles usually match
A 750 millilitre wine bottle exists because 750 millilitres is a standard of fill. The container industry built to the rule.
And why a US customary shelf is awkward here
Our bottles were built to ounces. Two of those ounce values happen to be on the list and the rest are not.
The ten that match are the ones to use
Three at 355 millilitres and seven at 473. Fill to nominal, label the nominal, no headspace penalty.
The 24 oz is a reasonable third option
Filled to 700 millilitres with under ten millilitres of extra headspace, which is inside normal practice.
Topping up is not a fix
Filling a quart bottle to 946 and labeling it 750 is a misstatement, and filling it to 946 and labeling it 946 declares a quantity that is not an authorized standard of fill. Neither direction works.
Nor is inert gas, on its own
Flushing the headspace helps and does not remove it, and it adds a step to a filling line that a correctly sized bottle would not need.
The three quart bottles are the ones to avoid
Nearly 200 millilitres short at the nearest comfortable standard, in a category where oxygen is the enemy.