How long does opened orange juice last in the fridge?

The short version: opened orange juice, kept cold and tightly capped, is usually good for about seven to ten days if it was pasteurised — noticeably less, closer to two or three days, if it was fresh-squeezed and never heat-treated at all. As with milk, the date on the bottle describes a sealed container. It has very little to say about the juice already sitting open in your fridge door, and the two kinds of juice above do not even start from the same place.

Three different products get sold as "orange juice"

The carton in the fridge case, the box on the shelf next to it, and the bottle from a juice bar are not the same thing, even when the label on all three just says orange juice. Refrigerated, pasteurised juice — usually labelled "not from concentrate" — has been heated briefly to knock down microbial life, then kept cold the whole way to the shop, which is why it needs refrigeration before you have even opened it. Shelf-stable juice, sold in an aseptic carton or bottle at room temperature, has been sterilised more aggressively and sealed to keep air out entirely; it is genuinely safe unopened on a pantry shelf for months, but the moment it is opened it behaves exactly like the pasteurised carton and needs the same care. Fresh-squeezed or cold-pressed juice — from a juicer at home, a juice bar, or a farmers' market — has not been heat-treated at all. It carries whatever microbial life was on the fruit and in the equipment, and it should be treated as the shortest-window, most conservative case of the three, closer to how you would treat a carton of cut fruit than a bottle from the supermarket shelf.

What actually decides how long it keeps

Temperature. The same rule as everything else that lives in a fridge: keep it toward the back of a middle shelf rather than the door. The door is the warmest, most temperature-variable part of the fridge, and juice sitting there is effectively getting a small head start toward spoiling every time it is opened.

How tightly it is capped. Juice is acidic, which is unfriendly to a lot of bacteria, but it is very friendly to the wild yeasts that are naturally present in fruit and float around any kitchen. Those yeasts need air to get going. A cap screwed on properly after every pour keeps that exposure to a minimum; a bottle left loosely closed on the counter overnight is giving them exactly what they need.

Drinking straight from the bottle. The same logic as a shared milk carton — every mouth that touches the opening introduces bacteria that were not there before, and it adds up faster in a household with more than one person doing it.

Which of the three kinds it is. Treat the fresh-squeezed or cold-pressed bottle as the one that needs the most caution and the shortest window; treat the pasteurised carton and the opened shelf-stable box the same way, since once opened they are functionally the same product.

How to judge it yourself, in ten seconds

• Pulp settling at the bottom is completely normal. Give it a shake before you pour. That is separation, not spoilage, and it is not evidence of anything going wrong.
• Smell for anything fizzy, yeasty or faintly alcoholic. That is fermentation — the yeasts mentioned above converting the natural sugar in the juice — and it is the single most reliable early sign that a bottle has turned. It usually shows up in the smell before it shows up in the taste.
• Look for anything fuzzy, especially around the cap and rim. Mould on juice is a clear, no-argument discard, not a "cut around it" situation the way it can be with a hard cheese.
• Taste a small sip if smell and look are both fine. Juice that is turning tastes sharper and flatter than usual well before it is unpleasant enough to be an obvious problem.

None of this is as high-stakes as judging raw meat — juice that has fermented a little is unpleasant rather than dangerous, and most people stop at the first sip. The genuine caution is with fresh-squeezed, unpasteurised juice specifically, which carries more of the fruit's own microbial load and deserves the shorter, more conservative end of the range rather than the benefit of the doubt.

Why day-nine juice tastes flatter than day-one juice

Even juice that has not gone off in any way that would stop you drinking it is quietly losing something the whole time it sits open. Vitamin C breaks down with exposure to air and light, and the bright, sharp top note of a fresh carton fades a little every day it sits open — noticeably by the end of the window, well before the point where it would actually be unsafe to drink. That fade is a quality question, not a safety one, but it is a genuine reason the last glass from a bottle rarely tastes as good as the first, and a reasonable argument for buying a size that gets finished within the week rather than a jug that outlasts its own brightness.

The thing that actually helps

The same low-tech fix that works for milk works here: write the day you opened it on the carton, because "sometime this week" and "over a week ago" look identical once a bottle is half empty and sitting behind three other things in the door. This is close to what Munch's opened-item tracking is built for — marking a carton as opened starts its own shorter countdown from that day, visible to everyone in the household, rather than the printed date being the only number anyone has to go on.