Bitterness Units

[Moley]

I don't want to sidetrack another current thread so can someone please explain this in simple terms.

I'm getting the idea of what different varieties of hops do, I think I understand about alpha acids, bittering hops and aroma hops but the forum's calculator defaults to 29% Utilisation, presumably for the full 90 minutes?

What's Utilisation? It's not in the forum's glossary, where does that 29% come from and what utilisation would you get from the last 15 minutes of the boil?

 

[Aleman]

Big topic really, but it refers to how much of the Alpha acids can be isomerised to iso alpha acids during the boil . . ie how much of the 'hop' is utilised. Hop utilisation varies due to a huge number of factors such as wort gravity, boil vigour, Boil Time, kettle geometry yada, yada, yada

Glens Hop Page explains it fairly well . . . and his Utilsation curve shows what happens according to his formula. Although a lot of his formula is fudge factors, it has to be to take account of the various elements that affect utilisation. . . . IMO using an empirically derived formula is a lot better than trying to come up with one that accounts for everything. . .Plus his formula/numbers match what is really going on. One of these days I will have my kettle(s) profiled (again) but as its a IBU test for every 5 minutes of the boil up to 120 minutes it will be frighteningly expensive. . . . Unless I can get a day on my own at Brewlab . . . But then I'll look at the effect of First Wort Hopping as well . . . and ultra late hopping

 

[EskiBrew]

The hop utilisation figure corresponds to the efficiency of the boil and is dependant upon many things: the vigour of the boil, the length of the boil, the specific gravity of the wort and the equipment used. In general the utilisation achieved will be in the range 2- to 35% under ideal conditions with a vigorous one-and-a-half hour boil and the hops boiling freely in the wort. Commercial breweries use the following equation to approximate utilisation efficiency:
Utilisation = (170 - degrees gravity) / 4
where degrees gravity for a 1.047 reading is 47.

The forum recipe tool uses an equation to determine the expected utilisation based on the ingredients and brew length. :thumb:

Edit: What Aleman said too

 

[Moley]

Thanks for the links Aleman, I will have a good read through that website this evening.

From the utilisation table, if I use 25% (1.050 wort, 90 mins.) and 11% (15 mins.) it should be as close as I would be bothered about.

Edit: Thanks eskimobob, although I haven't dabbled much with the recipe tool as yet.