What does 酿 mean in 苹果iPhone 5酿致命意外?
酿 means lead to/result in in that sentence.

As the original meaning of 酿 is "the process of making wine", the sentence


  A + 酿(成) + B


is a metaphor for "A leads to B (in a gradual/long-term process)", 喻事情积渐而成.



Issue of the causality

Personally, I think the sentence


  苹果 iPhone 5 酿致命意外。 Apple iPhone 5 leads to a fatal accident.


is not rigorous enough. Though it is acceptable, and one may complete the sentence in mind as


  苹果 iPhone 5 (的设计缺陷) 酿致命意外。 (The design flaw of) Apple iPhone 5 leads to a fatal accident.


So, a more logical sample sentence would be


  疏忽酿大错。 Carelessness leads to serious blunders.