1. Sterilize five 500 ml mason jars and their canning lids. In the bottom of a canning pot with the canning rack or large pot (with a cooling rack or steamer), place clean, empty mason jars, right side up. Cover the jars completely with hot (not boiling water), at least an inch or so above the mouths of the jars. Turn on heat, and bring the water to a rolling boil. Once water begins to boil, start timing the sterilization process. Boil for 10 minutes to 15 minutes. Turn off heat.
2. Once the bubbles have subsided, submerge the canning lids into the hot water. Do not boil the canning lids, as this may cause the adhesive ring in the lid to deteriorate and create a poor seal. When ready to use, carefully take the jars out with tongs. Carefully pour the water out of the jars and place right side up, onto a clean kitchen towel. Alternatively, leave the jars in the hot water until needed.
3. Peel onions. With a sharp chef's knife, cut onions into ⅛ (3 mm) to ¼ (6 mm) of an inch thick rings. Place into a bowl, until ready to use.
4. In a medium large pot over medium heat, place vinegar, water, kosher salt, and Redpath® Granulated Sugar, bring to a simmer. Stir to dissolve sugar and salt; about 3 minutes. Set aside.
5. In each of the sterilized jars, add 1 teaspoon each of peppercorns, mustard seeds, coriander seeds, and a bay leaf. With a pair of clean kitchen tongs, divide the sliced red onions evenly amongst the 5 jars.
6. Ladle the hot vinegar mixture into a measuring cup or a container with a lip. Pour the hot liquid into each jar, covering the onions but leaving about ¼ (6 mm) to ½ inches (1 cm) of room at the top. Gently press onions under the brining liquid until submerged. Wipe the rims of the jars with a clean kitchen towel or damp paper towel.
7. From the hot canning water, take out the lids. Place seal onto the tops of the jars. Screw on the outer ring until just tight.
8. In the same hot water used for sterilizing the jars, place the warm jars of onions back into the water. Bring the pot back to a simmer (between 170°F (77°C) to 180°F (82°C)). Once the water reaches that temperature, start timing the canning process; 10 to 15 minutes.
9. After the time is up, quickly and carefully take jars out of the hot water. Place jars onto a clean kitchen towel and allow to cool and rest for 24 hours. Refrain from moving the jars. Keep processed jars that are sealed properly in a cool, dark place. The pickled onions should keep for up to a year. If a jar has not sealed properly, keep in the fridge for up to 2 weeks.
