Beer critique: How do they differ - wheat beers

[Keqwow]

I have become more and more interested in wheat beers. I am actually thinking about trying to brew my own, but I feel like I first need to have an understanding of some of the basic differences. I realize there is a good book out on the subject of brewing with wheat, but I was hoping you guys might be able to give this beer-beginner some straight feedback from a few examples I currently have sitting in front of me. I decided to do a small tasting this evening and brought home a couple examples. I only opened three for now. I decided to compare a Harpoon UFO White, Harpoon UFO Hefeweizen and a Paulaner Hefeweizen. Definitely an interesting comparison. I am sure you guys are much more familiar with terminology than I am at this point and are likely familiar with these beers. I don't note a whole lot of difference between the UFO White and UFO Hefe except that perhaps the Hefe is slightly more bitter. What specifically might actually cause this difference?
Alternatively, and much more interestingly, the Paulaner is definitely different from the Harpoon beers. The key difference is what I believe is described as a strong banana flavor which is something I note much more in imported Hefeweizens. What is causing that flavor?

I appreciate the input. Just trying to be really basic about all of this and figure out what causes certain flavors that I like and don't like and how they differ.

 

[Teromous]

It's hard to speak specifically about those beers, because I haven't tried the two UFO beers you've mentioned. I have had Paulaner Weiss but I don't remember how it tasted

The banana flavor you are tasting is known as isoamyl acetate. It is a byproduct of the yeast used in fermentation. Different yeasts will result in different amounts of this flavor, and they should be carefully selected for their ability to produce it. There are three popular ways (that I know) of manipulating this flavor. The first, is by manipulating the mash. Conducting a decoction mash causes a difference in enzymatic activities that allows the yeast to become diauxic, whereby it produces more esters by increasing acetyl CoA production. The second is by increasing the temperature of the fermentation, which also has been proven to increase acetyl CoA. The third is by reducing wort aeration, which similarly increases acetyl CoA. Essentially you are doing everything in your power to stress the yeast and decrease its ability to grow/reproduce.

There is a fourth way, which is increasing the gravity...but normally for a wheat beer you're not looking for a really high gravity anyway.

 

[KeyWestBrewing]

Is the bitterness a hoppy one? More hops obviously imparts more bitterness so that could be a difference. The banana aroma is coming from the esters the yeast put out. Different Hefe yeasts have different ester profiles ranging from banana and clove to bubblegum. What temperature the beer is fermented at also influences what ester profile you end up with.