They are 2 very different compounds, both organic, but with differing effects on food and very different purposes. Ascorbic is a food preserver - primarily color - while imparting no acidic taste and does not change the pH of the food nor does it have any antimicrobial properties. Citric acid is a natural food acidifier in that it changes the actual pH of the food as well as the taste. So when drying food it is the color/appearance of the food you want to preserve. But citric is required when ever you need to increase the acid pH of the food. Citric acid is also a natural antioxident, antimicrobal, and germicidal which is why you often see it in cleaning solutions. Not that we want to scrub down the kitchen counters with our tomato juice. ;) They cannot be used interchangeably in canning/home preserving. Dave Here is a link that might be useful: Are Citric Acid and Ascorbic Acid Twins?

KeitasKookie, There should be enough vinegar or other acidic ingredient to minimize the oxidation on the top layer. What recipe did you use? Was it adequately acidified? One reason might be too much headspace (the distance between the top of the jam and the rim of the jar). If it's more than 1/4", that could very well be the cause. Storage also makes a difference (dark, cool cupboards will produce less discoloration). Lighter colored fruits/vegetables (like orange peppers or certain varieties of strawberries or raspberries) are also more prone to discoloration due to the amount of polyphenol oxidase enzyme inherent to the food.

NO NO NO... Vitamin C is ASCORBIC ACID. Citric Acid has similar uses as ascorbic acid and is an acid derived from fruit. You can get it from most health food stores. Fresh Fruit is a combination of ascorbic acid (aka vitamin C) AND citric acid and might do the trick in a pinch. I use citric acid for sprouting (beans/seeds), canning, drying or freezing. It aids in preserving the Vitamin C content in fruit. It also retards spoilage by bacterial growth and prevents discoloration. I use a dip of 1 t. per quart of water or juice for most fruits and vegetables when dehydrating them. -Grainlady

Sour and bitter are not the same thing. If you want to know the difference compare these two lists to each other: Sour (this is what acidic as a flavor—not as a pH, necessarily—refers to, IMO): * Lemons * Vinegar * Vitamin C (ascorbic acid) * Citric acid * Malic acid * Oxalic acid * Unripe fruit * Green apples * Cornelian cherries * Sour cherries * Some kinds of tomatoes, some years (not grocery store tomatoes) * Fresh pineapple * Sorrel * Rhubarb Bitter: * Magnesium chloride * MSM * Baking soda * Cocoa powder * Arugula * Pumpkin (some kinds, anyway, like the store-bought kinds usually are) * Tylenol Some things, like grapefruit, are sour, bitter, and sweet at the same time. Cucumbers can become sour like lemons, or bitter like arugula, but I haven't seen both at the same time. People tend to strive to avoid both. Sour things often taste good with sugar. Bitter things tend to leave a sweet aftertaste. Too much of a sour thing might hurt your tongue and make you constrict your face and squint. Too much of a bitter thing might make you gag.