If canning, prepare your water bath canner and jars before you begin making the jam. The canner should be at a simmer, about 180 F.

Wash your berries and remove any stems. If you come across any berries that are soft or damaged, get rid of them. Do the same for the rhubarb - give it a good wash and prep it for the jam-making process by chopping it into fine, relatively uniform pieces. 

Mix all your ingredients together in a large, nonreactive pot. Give it a good stir and bring it to a boil. Once it's boiling, turn down the heat to a medium simmer for about fifteen minutes (or until it's thick). 

Ladle hot jam into warm, prepared jars. Use a funnel to make sure you don't make a mess, and when you transfer the mixture, leave about half an inch of space at the top. 

Clean the rims of your jars with a dampened, clean, lint-free cloth or paper towel to make sure no food residue remains. 

Be sure to leave 1/4 inch headspace, and cap the jars to finger tight with 2 part canning lids.

Once all your jars are ready, place them in the water bath canner.

Increase the heat and process the jars in a boiling water bath canner for 10 minutes (or 15 minutes above 6,000 feet in elevation). 

Once the processing time is complete, use a jar lifter to carefully remove your jars and place them on a towel-lined surface for twelve to twenty-four hours without disturbing them. 

After the jars are done cooling, check the seals. Label, date, and store for up to one year.