No, it has gone off.
Yes, pineapple juice can be turned into pineapple vinegar. Raw Pineapple Vinegar is made using thinly sliced pineapple, brown sugar, cloves and water. There are several detailed vinegar recipes available on the internet.
The pineapple juice is acidic; the color with pH paper Merck no. 9565 is red to brown.
Clarified pineapple juice is a natural pineapple juice which gets filtered to remove the pulp. The taste and texture of clarified pineapple juice is more refined. Many brands prefer to have a clarified pineapple juice for canning purposes.
Pineapple
48oz
Is pectin used in unsweetened pineapple juice
5.6 quarts
yes
1 pineapple
Yes, if it's brown and smells, it's bad.
Tropical juice that has a strong taste of pineapple
Anything acidic - I would use white vinegar.