How to select inner mesh???

I’m new to Blender and doing this tutorial > http://www.blenderguru.com/tutorials/make-beer-blender/ I’m to the section where you select the inner area to create the beer look and I can not figure out how he selects just the inner portions of the glass model. I have Googled it over and over.

Apologies for being a newbie. I’m sure this isn’t hard to do but I can’t get it.
Thanks

Next time include a timestamp that goes to the relevant part by right clicking on the video and select ‘copy video url at current time’ or similar depending on the browser.

He’s selecting it with edge loop selection and adding to it. alt+select to select any edge loop, and alt+shift+select to add the loop to the selection.

But it’s always slow to do sequential selections one by one and you might select the wrong thing. Would be more controlled to select a loop from the bottom half or whatever mesh element is at the bottom of the glass and then ctrl+numpad_+ to increase selection. If it’s hard to get to, could use clipping border (alt+B to draw and toggle off) to isolate an area where the bottom part is and do the initial selection, then increase selection as much as you want. Like this https://dl.dropboxusercontent.com/u/26346140/select_inner.mp4