# Which gas makes Orange juice bottles swell?

I forgot a bottle of 1L Orange Juice (100% orange juice with pulp) in the fridge for about a week, the bottle was previously open so air got inside as well.

After a week the bottle got inflated and when I opened it I could hear the gas coming out. No odours, orange juice still the same colour (not sure if the same taste, I threw it away).

Which gas was produced and how did it happen? The air that got in seems to have played a part on it (these bottles stay in the supermarket closed for a long time without getting inflated).

• What temperature was the bottle when you opened it and heard the gas coming out? To be more precise, did you take the bottle out of the fridge, leave it closed inside a warm room for a while, and then try opening the bottle? – Nicolau Saker Neto Mar 3 '15 at 3:11
• No, the bottle was already inflated inside the fridge but if I keep it outside it inflates faster. – user1894919 Mar 3 '15 at 3:24
• CO2, produced from sugar by yeast that came in through the air. Although i thought orange juice would be sour enough to keep yeast from growing. – Karl Feb 1 '17 at 7:27

I can't imagine the gas was anything except $\ce{CO2}$ formed by the action of microorganisms contaminating the orange juice. They degrade the organic components of the juice to power their metabolisms, and produce carbon dioxide as a byproduct.