Brewday 18/2/07 questions first......

[louthepoo]

thanks for that detailed explanation Frothy, glad its that simple then

well it tastes nice anyway!!

[bitter_dave]

thanks for that detailed explanation Frothy, glad its that simple then

well it tastes nice anyway!!

Hops obviously have different levels of bitterness, and between seasons there can be quite a lot of variation in the bitterness of hops; hop bitterness is measured in alpha acids or AAUs which is basically the bitterness provided in relation to the weight of hops.

For example, I recently used styrian goldings; the recipe I used assumed the hops had an alpha acid of about 8, but my hops had an alpha acid of about 4. This means that the hops had half the bitterness that the recipe assumed. If you stick to recipes, and the recipes give the alpha acid assumed for the hops, you can very simply adjust the amount of hops needed using the following equation:

(weight of the original hop in the recipe x the alpha acid of the hop assumed in the original recipe) / the alpha acid of your hops.

Therefore, assuming the recipe says to use 40 grams of Styrian goldings with an assumed alpha acid of 8 AAUs, but your hops have an AAU of 4, the weight of styrian goldings you should use:

(40 x 8 ) / 4 = 80 grams.

This adjustment does not apply to hops added at the end of the boil, or after the boil, as not much bitterness is extracted from late hops.

I hope this is helpful; frothy's post above is also worth getting you head around.

[bitter_dave]

IBUs represent the amount of bitterness in the final beer. Working out the IBUs roughly, if you are putting a recipe together, is really rather simple.

Let's say you make a beer with an original gravity of 1040, and you want to have a bitterness of 30 IBUS, which is not untypical for a beer of that strength.

OK, you want to use the styrian goldings mentioned above, which have an alpha acid of 4. Using Wheeler's method to get 30 IBUs from the hops for 25 litres of beer you can work out roughly how many hops to add:

(IBU desired x volume brewed) / (alpha acid x 2).
So, in this case:
(30 x 25) / (4 x 2) =
(750) / (8 ) = 93 grams.

This is for the hops at the beginning of the boil, boiling for 90 mins. There are disputes about how much bitterness is extracted from hops etc., but this is a relatively simple (I hope) way of approximating how many hops to use to get a desired level of bitterness.

I hope this makes sense