If you want some vitamin C, where do you turn? Most people might say orange juice.

So you go to the grocery store — and that’s where it gets complicated.

Take a look at fresh-squeezed, raw juice. Despite what you might think, this juice may contain low amounts of vitamin C. One reason is that orange varieties differ in ascorbic acid and water content, possibly making a very dilute juice. Secondly, crushed fruit contains active enzymes that can start destroying the vitamin C as soon as it’s squeezed.

What about commercially available juice that is “Not from Concentrate”? Juice makers go to great lengths to produce a consistent product not seen in the raw juice, using large batches of oranges from a variety of sources and methods to deactivate enzymes in the fruit. However, this juice is also pasteurized, and heat destroys vitamin C! Many manufacturers add it back to make up for this loss.

There is another wrinkle: vitamin C is destroyed not only by heat but also by light and oxygen. Studies have shown that vitamin C continues to disappear in the refrigerator. Further, vitamin C disappears faster at 50°F (10°C) compared to 40°F (~4°C) or lower. While most home refrigerators are around 35-40°F, but those open cases at the grocery store are warmer.

Other studies have shown that orange juice packaged in polyethylene or polystyrene can let oxygen inside, causing the vitamin C to degrade over time. Clear plastic containers let in light that accelerates this process as well. And, what’s more, this doesn’t stop once you take the bottle home.

Another option is frozen: frozen orange juice concentrate actually contains the most vitamin C. In addition, freezing stabilizes it for long-term storage. Good, right?

Well, not quite. Studies have shown that reconstituted orange juice from concentrate loses ascorbic acid faster than bottled juice purchased from the store. It is not entirely clear why, but it may relate to the metals in the water used (iron and copper can destroy vitamin C), the acidity of the liquid (it is more stable in acid), and/or more exposure to oxygen.

Now that you know this, what should you do?

The chemistry may be complicated, but it doesn’t mean you should stay away from orange juice. If you load up on lots of sources of vitamin C, you can make up for any loss due to storage or processing.

Just use it as a lesson that with vitamin C, everything is not necessarily simple.