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| Preserving Headspace Tool Alternative: "kitchen only" ruler |
Headspace is the distance between the top of the
food (i.e. jam) or liquid (i.e. brine/syrup) in the jar and the jar rim. You
can measure this distance with a headspace tool (pictured, right) or you could
use a clean plastic ruler instead. It's important to fill jars, remove bubbles
using the other end of the headspace tool (or using a non-metallic utensil,
like a chopstick), and then measure the headspace of every jar precisely before
adding lids to ensure you are preserving safely. Headspace does vary depending
on what you are preserving and which method you
are using (boiling water bath or pressure canning).
Why do we need headspace?
Leaving this space between the jar contents and
the jar lid allows sufficient room for the contents to expand during boiling
(processing). The hot air in the headspace also expands and rises to the top of
the jar (below the lid), and this air is forced out the jar. This results in
a high
quality vacuum seal when the air cools and pulls the lid down
tightly after processing (usually within a few minutes after processing you
will see and/or hear this happen), but it is important to cool your jars
overnight - ideally 12 hours - before removing bands (or clips) from jars and
storing your preserves.
An incorrect headspace could result in a poor seal.
If there is too much headspace, this will result
in a "false seal". The hot air cools and pulls the lid downwards, but
there is still excess air remaining in the jar. Over time, jars may become
unsealed, harbour mould growth and/or discolour the surface of the
jar's contents.
If there is too little headspace, this could
result in a bubbling mess as the jar contents are pressed out of the jar when
boiling (during processing). Some of the contents may become wedged between the
lid and the jar - so the jar will not seal properly and may unseal over
time and/or allow contamination.
Pressure canning is at a higher temperature than
boiling water canning, which is why the headspace is more (1 inch) for pressure
canning. During pressure canning, the air (and jar contents) heats up more and
needs more room as it expands and boils, compared to the headspace required for
water bath canning.
Which headspace do I use?
ALWAYS follow the headspace specified
in your preserving recipe, a basic guide is:
1/4 inch (0.6cm) Headspace
Chutneys, Fruit Butters, Jams, Jellies, Marmalades &
Spreads [Boiling Water Bath Canning]
1/2 inch (1.25cm) Headspace
Fruits, Pickles & Tomatoes [Boiling Water Bath Canning]
1 inch (2.5cm) Headspace
Fruit Pie Filling [Boiling Water Bath Canning]
Meat, Stock, Soup, Non-Pickled Vegetables, etc.[Pressure Canning]
Author: Megan Radaich
Image Credit: Megan Radaich
Publication: www.foodpreserving.org