Place 7 clean 250 ml mason jars on a rackin a boiling water canner; cover jars with water, and heat to a simmer (180°F/82°C). Set screw bands aside. Keep jars hot until ready to use. Preheating Bernardin® lids is not advised.

The sealing compound used for our home canning lids performs better at room temperature than it does pre-heated in simmering water (180°F). Simply wash lids in hot, soapy water, dry, and set aside until needed.

Preheating can lead to less vacuum being achieved during water bath canning, and to buckle failures during pressure canning. In a large bowl, combine prepared green and banana peppers, red pepper, if using, apples, cabbage and salt. Let stand 2 hours; drain well.

Combine vinegar, sugar and mustard seed in a large stainless steel saucepan. Bring to a boil; reduce heat. Add drained pepper mixture and boil gently 10 minutes. Ladle relish into a hot jar to within 1/2 inch (1 cm) of top rim (headspace). Using nonmetallic utensil, remove air bubbles.

Wipe jar rim removing any stickiness. Centre hot sealing disc on clean jar rim. Screw band down until resistance is met, then increase to fingertip tight. Return filled jar to rack in canner ensuring jars are covered by water. Repeat for remaining relish. Cover canner; bring water to a boil.

At altitudes up to 1000 ft (305 m), process -boil filled jars - 10 minutes minutes.* Remove jars without tilting. Cool upright, undisturbed 24 hours; DO NOT RETIGHTEN screw bands. After cooling check jar seals. Sealed discs curve downward. Remove screw bands; wipe and dry bands and jars.

Store screw bands separately or replace loosely on jars, as desired. Label and store jars in a cool, dark place.

Processing: At altitudes up to 1000 ft (305 m), process -boil filled jars - 10 minutes - 10 minutes.

Altitude-adjusted processing table: At altitudes up to 1000 ft (305 m), process -boil filled jars - 10 minutes