Can you mash bananas?

That hefeweizen banana flavour is quit elusive isn't it !

For a wheat beer it's OK to put them in at the end of the boil, say at 5 minutes.

For a ~20 litre batch, I like to add a pair of quite ripe bananas, mashed with a fork (not black bananas, spots ok, not off) at 5 minutes. This gives a slight banana aroma and flavour.

I like this because it's simple, and reduces the risk of infection.

I've heard you can also add up to 5% dextrose to help the wheat beer yeast go a bit crazy during initial fermentation, and enhance ester production. I am yet to try this though.

I've made a banana beer before. Lots of bananas & some brown sugar. It didn't taste like bananas (except a faint hint after swallowing). It tasted like a lo-dollar asti spumanti & ±13% (ok, so quite a bit of brown sugar). As close as I recall, 10 lb bananas, 5 lb brown sugar, 2 lb Munich malt (to do the starch conversion & give a whisper of that Munich flavor) in 5 gal. 150° mash 45 min (extremely difficult to lauter). boil to clean-break. EC-1118. This is from 10 year-old memory; the only part I fully recall is 13% & asti spumanti flavor.

Edit: learned a bit more using bananas in winemaking. Many fruit wines are a bit thin & banana adds body. Using an open boil, most of the aromatics (flavor) of the bananas go away. Placing the cut up banana in a ziploc bag with a little water & amylase kept at 140-145 for 4 hours the banana flavor remains & the starches turn to sugars. Works well both ways, just depends on what you want to accomplish. I maintained the temp by placing the ziploc in a crock pot that was plugged into a temp controller. If you have a sous-vide rig that would be easier.

If you put banana in the secondary it is quite the mess that takes a very long time to clear up. Of course, that may help in getting more aging time in.

I don't know why mashing them would add MORE banana flavor than using them in secondary. You'll get more sugar by converting what little starches remain in the fruit (depending on ripeness). But conversion of starch to sugar isn't related to how much banana flavor compounds are present in the fruit. Just "mash" them with a fork and put them in secondary.

Anytime I add fruit, I put it in the secondary after primary fermentation so the yeast is gentler on the fruit leaving more of the fruit flavor behind. I'll usually give the beer a week in the secondary before I add the fruit. Banana is a fantastic idea though, you guys have me excited. I'm going to try this out.

It can be done, as Seth pointed out when referencing Wells' offering. I don't know if you'd want to mash them, though, or if you'd just add them to the secondary. Bananas have a very strong flavor, especially ones that are flecked with brown. If you're going to try it, maybe you could also infuse some nut flavor and make a proper Bluth Banana Stand Ale.

I'm not sure about when you would want to include them in the process, but Wells makes a Banana Bread Beer, so it can definitely be done.

I also came across this article about a Hefeweizen mixed with banana nectar, like a banana version of the Austrian Radler, so you might be able to try incorporating it at the end of your brew somehow.