Green apple flavors

I brewed a ginger beer 4 weeks ago. The wort had a nice amber color and it went light on the hops. When i moved it from primary to secondary two weeks ago it had some residual sweet flavors with none of the of sour apple taste that young beer typically has. I moved it to bottles and it had that nasty sour apple taste. I expect this to disappear over time as the beer bottle conditions but I want to understand what causes the flavor.

I am fairly new to brewing and this was my second batch using a secondary fermenter. I realized that i have never tasted my beer two weeks into the process. I just assumed that the sour apple flavor appeared right away and just got better over time. Can someone give a robust explanation of the sour apple flavor? Facts and science are appreciated. Googling has given me conflicting explanations.

You are right, it should disappear over time.
From JP"s HTB:

John Palmer said:

Acetaldehyde
A flavor of green apples or freshly cut pumpkin; it is an intermediate compound in the formation of alcohol. Some yeast strains produce more than others, but generally it's presence indicates that the beer is too young and needs more time to condition.

Click to expand...

So why did it not taste like this the first time I tasted it when it was even younger? Should i have given it another week in the fermentor before bottling?