Apple Juice - Canning

Ingredients
8 Quarts Apples (12) these amounts will yield about 2.5 gallons
6 Quarts Water (boiling) (9)
2 T Cream of Tartar (3)
1 Cup Sugar +/- to your liking Depends on the sweetness of the apples.

Wash the apples remove bad spots and quarter the apples. Measure and place the quartered apples into a 5 gallon pail with a sealable lid. Do not need to remove cores, stems or seeds.
Boil the water and add the cream of tartar when the water is boiling, and pour the boiling water over the apples and completely cover the apples with the water, let stand for 24 hours. (May have to place a plate and jar over the apples to help keep them covered.)
Strain the juice through cheesecloth into a large pan, add the sugar and boil for 15 minutes. Pour into clean and sterile sealable jars and turn upside down for 5 minutes for lid seal to set and turn back over and let cool. Store in a cool dark place.

Science
Question answered about cream of tartar…Why does the cream of tartar bring the juice out of the apple? One more way cream of tartar gets used in the kitchen is when we're working with sugar. Where cream of tartar is a stabilizing agent for egg whites, a pinch added to boiling sugar is actually an interfering agent. The cream of tartar gets in the way of sugar's natural tendency to bind together and prevents those dreaded sugar crystals from forming.
Cream of tartar is also an acidic by-product from the process of making wine. It's found in the sediment left behind in barrels after the wine has been fermented, and it gets purified into the powdery white substance that we use in baking.
Cream of tartar is also often added to baked products to help activate the alkaline baking soda. In fact, cream of tartar mixed with baking soda is what gives us baking powder.
http://www.thekitchn.com/thekitchn/food-science/food-science-what-is-cream-of-tartar-072125 7-28-2010