This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
>From Emily Dashiell (email@example.com)
I found my first collection of half-gallons at a garage sale. Priced at
$3/doz, it was a steal!!! I bought several doz; then thought about it some
more, and drove back the 8 miles and bought more. I did see new boxes of
them, in a large chain store (like Home Depot or some-such), and the price
was $15/doz and that was 5+ years ago! Made my bargains look even better :)
You could make them into terrariums; you could build a model in one; you can
make vinegar in bulk: raspberry, orange, assorted herb types, etc. Lotsa
uses, just use your imagination.
Generally we say: Do NOT use half-gallon jars for canning. However if you use
100% water-like liquids you may use them. Canning water? Juice? Freeze it.
or: High acid foods may be stored in such jars - be SURE the aicd is full
5% - use ONLY pickling vinegar which is clearly labeled at 5% acid. If 3
cups 5% vinegar is used with 3 cups water - that is NOT a 5% acid solution.
Home made vinegar and / or cider vinegar are not suitable. If the acid level
is suspect - bump it up with glacial citric acid. If using non-standard vinegar
you MUST test the acidity - preferably by acid titration.
The issue with using half-gallon (1/2) jars for processing is that of heat
convection. We know full well how the viscosity of a food affects processing in
half-pints, pints and quarts. We know that fish is nearly always processed in
half-pints. Pureed pumpkin / squash is no longer recommended for home canning
as the viscosity is such that heat penetration to the core is rarely reached in
even pint sizes.
Commercial processes that use half-gallon jars are exacting ones which use high
temperature steam in equipment which records the temperature and time. High
temperature flash pasteurization is common also.
Regardless of the origin of food in half-gallon jars, the issue of oxidation
rears its ugly head. Once opened, the food degrades rapidly even when safely
processd at source. Commercial processors then add anti-oxidants, gums,
sulfites, modified corn starch, benzoate and other
'goodies' to stave off degrade.
Here is an example: Commercail 4% red wine vinegar in 1 gallon glass jar from a
reputable manufacturer. It is stored in a food cellar along with other canned
goods. Usage is over 6 months unless in canning season. It is quite common for
the remaining two inches of depth to oxidize ( goes brown) to the point it is
useless and must be discarded.
The wise kitchen master will procure the size that blends price effiency and
quality. Throwing out 1/4 of a large container makes little economic sense.
Container size, as all smart preserves know, is suited to serving size.
The risks associated with jars larger than 1 quart or 1 liter are not trivial.
Due to the mass of the large jars, food may be botulitic at the core with little
visual evidence of it. Those who think the bulging lid is the tip off of content
activity can be sadly mistaken. Seldom will the lid of a large jar show any
sign. The reason for this is compressibility of gases. The internal size of the
jar is such that gases produced by a live culture at the level of toxicity can
be easily accomodated without pressure being induced.