Beersmith Extract IBUs

[Tomgm14]

Hi,

I have so far only brewed all grain, but today I wanted to knock something out quickly so I decided to to a small batch using DME (12L batch using 2kg light DME).

When I was formulating my recipe, I noticed that a "normal" amount of bittering hops didn't give me anywhere near the IBUs I was looking for. Secondly, when i moved the batch size to 23L, it gave me a much more expected IBU figure.

Can someone explain what's happening here? I'm probably missing some fundamental point re: utilisation, but I'd love to understand what's happening.

Here is my recipe for reference:

2kg Light DME
30g Bravo (60min, 15.8%AA)
20g Cascade (10min, 8%AA)
15g Cascade (W/P, 8%AA)

With the batch size set to 12L, Beersmith gives me 17.8 IBU, but when I set it to 23L, it gives me 54.8 IBU.

Cheers!

 

[manticle]

There is a relationship between wort gravity and hop utilisation. It's been empirically observed but causes are still hypothetical as far as I understand and do not necessarily relate solely to more sugar = less utilisation.

 

[TwoCrows]

Your OG and FG are very high. That is also a lot of hops for your Gravity. Even with a 23 ltr boil is to high.

Try out http://aussiehomebrewer.com/topic/29655-kit-and-extract-beer-spreadsheet/

 

[manticle]

How do you know what the FG is twocrows?

 

[Lyrebird_Cycles]

The relationship between wort extract and utilisation is captured in Tinseth's calculator as a "bigness factor"* .

If your DME is 5% moisture I get 15.8 oP for 12 litres and 8.2 oP for 23 litres, the Tinseth calculator will give 91% utilisation in the first case and 123% in the second, which does not account for the difference shown. IMO it's a mistake in Beersmith**.

Putting your figures into my calculator gives 53 IBU for the 23 litres and 101 IBU*** for the 12 litres.


* I don't like Tinseth's factor so I use Avnet = Av0 * 1.038^-P * pH / 5.2 where Av0 is a factor to account for initial loss (alue generally around 0.75) and P is the wort concentration in Plato.

** IMO this is all too common, I no longer use the calculators in Beersmith.

*** With the proviso that any value above 70 is to be treated with suspicion.

 

[TwoCrows]

Using the spreed sheet , 2.0 kg of ldme in 12 ltr using US05 gives og 1.063 fg 1.016