Why is there so much foam when I open the bottle?

This is called gushing, and you usually get it with a combination of two factors:

1. A lot of CO2
2. A lot of "crystallization nuclei" for the CO2 to build bubbles and gas out

I currently have such a beer - I added more sugar in order to get more than usual CO2 and something went wrong during the brew and the beer got very cloudy. Every bottle I open gushes almost immediately.

Once you have that, there's not much you can do. Cooling the beer down to almost freezing temperature and then pouring it out immediately after opening the cap.

FWIW ... I used to make root beer from scratch, using either champagne or ale yeast for carbonation. SWMBO used to open the bale-top bottles with a bit too much of a flourish, and they would gush every time. I would open them very gently, very slowly, with no problem. So I had to train her to take it easy, because it seemed obvious to me that popping the bottle very suddenly would lead to a violent gushing reaction. Not sure if this is a factor with your gushers, but perhaps it's worth considering.

By the way, absolutely no innuendo is intended by this post. ;)

Cheers!

Sometimes when opening a beer to early after bottling, it will foam, and taste flat. Especially when you have high carbonation. 5 oz in 5 gallons equals a co2 volume of 2.9 which is quite high for an american ale. When I bottle my belgian ales I usually have a carbonation around 3. These will foam if opened too early but after a few weeks they will have a nice carbonation and wont foam at all when opened.

I would wait a few weeks and keep them in a safe container before jumping to any conclusions. After two weeks put one in the refrigirator and leave it there for a day before opening. if it still foams then you have bigger problems.

If you see something that looks like a white ring of sediment in the bottle around the neck, then you probably have an infection.

One possibility is uneven blending of the beer and priming sugar solution. Did you mix the sugar/water solution yourself, or just let it mix naturally from the beer being racked on top? Depending upon how viscous it is, it can sit at the bottom of the fermenting bucket even though the beer is swirling. This means you end up with some bottles undercarbonated, while others are overcarbonated.

Some people try to use as little water as possible in the priming sugar solution, so not to dilute the beer too much, but this can backfire! Best to use a little more water to be sure it's uniformly mixed with the beer.

One of three things:

1. Incomplete fermentation prior to bottling... If the beer wasn't completely done before bottling residual sugar (plus priming sugar) is over carbonating the beer.

2. Too much priming sugar. Re-examine how much you used. Consider that if the beer was significantly cool prior to bottling that a fair amount of CO2 would have been already in the beer post fermentation. Hence the priming sugar needed to be adjusted. This shouldn't really be a problem if you were fermenting it as an ale as you indicate.

3. A contaminating microbe got into your beer and that microbe is fermenting away on the non-fermentables left by the brewers yeast. It is possible to have a contamination that creates gushers prior to really tasting any off flavors as well.

You might be able to rescue the brew by venting caps by lifting them partly and then re-capping to off gas some of the CO2. If you can chill the entire batch of bottles down to fridge temp, you might prevent more CO2 from developing. Also storing them super cold prior to opening might help keep some of the CO2 in solution. In reality, if you have gushers, there isn't alot you can do to remedy it now. Sorry.