centering text on height

How can I center text in element on height?

for exmaple:

from this: http://ift.tt/1D3fI2Q

to this: http://ift.tt/1CmJFbf

I know I can write the height: property on the text and then use

position: absolute;
top: 0;
bottom: 0;
margin: 0;

but I don't want it because the height of the text is changing some times because I can have a couple of lines..