Home brewing - alpha acid content of hops?

Not sure where you've read about Hallertau at 7.5% alpha, but

unless you're dealing with Hallertau Tradition that seems to be

a bit high. Most Hallertau (Hersbrucker, Hallertauer, Mittlefreuh,

etc.) run in the 4%-6% range, and alpha content can vary widely

between crop years. Go with what is on the package and adjust

your hop additions to achieve the target IBU listed in the recipe.

I believe the use of a recipe is merely to tell you what the ratio of each hop should be in the beer and what the total bitterness you should be aiming for.

As such, you need to adjust each recipe for the specific hops you are using. Not doing this should make the beer less bitter which could be perceived as slightly sweet or malt biased. This isn't necessarily a bad thing, both ways may end up with good beers, but the difference is that one is the recipe (when you alter the weights) and one is your modification (ironically, following the weights in the book).

All you can do is buy a high strength yeast, turbo or something they are called, available from specialty brew shops. Problem is the yeast will only ferment until either the sugar is all metabolised, or the alcohol concentration kills the yeast. Use one of those floaty things, it's been years since I made beer to see how much sugar you got left vs how much alcohol... best thing is buying a high strength brew I used to make 9-10% beers that were pretty tasty & definitely flipped you up. Mucking around with off the shelf beers aint gunner do it, gotta get a good malt, not corn syrup!

Go by what the label says; different batches of hops vary a lot. Unless you got a really great buy on hallertau, why are you wasting this noble aroma hop by using it as a bittering hop? Why not go with something like Chinook or Galena?