I bought a bag of yogurt  that was in cold store yesterday in a supermarket nearby my dwelling,I put it on desk without chilling and plan to drink it on the day.But in fact I forget that I need to drink up it and on the second day I find the bag which should be flat all the time become a round ball.What strange is! The first time I see such an odd phenomenon in my life.I think it's degenerative and intend  to put it as an interesting ornament on my desk until the bag ruins totally.You can see the following pictures,that's amusing.[s:267]
[img]http://l.paipai.fm/118851/photo/Mon_1206/27743_65751339826088127064f9e7c77c1.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_b5b213398260817ec98eb70c4c77c.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_7c17133982608045d656460001978.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_494f1339826078d67ea95051646ff.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_9db3133982607726436475709d4b2.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_1dbd13398260696e1224e97f037ab.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_d96e133982606889462b36ebafcf7.jpg[/img]


[img]http://l.paipai.fm/118851/photo/Mon_1206/27743_91bd13398260922a2ca0dc31a2850.jpg[/img][img]http://l.paipai.fm/118851/photo/Mon_1206/27743_70071339826066f0b852d2bf7b094.jpg[/img]

Not long time,it's maybe only one minute later my new find ,the bag has some cracks that the ornament also loses....[s:271]

Thanks for your explanation and I understand from your words. The bag is round now although the yogurt almost runs out.I promised someone to show the yogurt ball to him in next month. Good night.

Hah, that was an interesting experience.

As a student majoring in chemistry, I could tell you the reason behind.

These days, because the temperature is rather high, the yogurt tends to continue to ferment. The process of  fermentation gives off gas, which makes the yogurt bag expanded.