Hop Utilisation in the Whirlpool

[krausenhaus]

So spec/HPLC grade solvent is about $100 a litre, which is $2 per sample. Why do you need to cold store your blank and redo it each time? Just record a baseline and be done with it.

I generally blank before reading each sample because the spectro I use is an unreliable piece of shit.

Each sample requires 20 mL isooctane and about an equivalent amount for a blank (which you could store and use multiple times in a day). You also need access to a centrifuge, a shaker and various consumables such as disposable pipettes and PPE etc. which add to the cost. The actual labour is 30-40 minutes of an analysts time (I'm a slow and clunky PhD level organic chemist doing this in my spare time), but for this amount of work/testing you could expect to pay around $130-150 commercially.

So mix 50/50 wort/isooctane, on shaker for a while, spin down, remove organic fraction and read in spectro?

Is isooctane a commonly used organic solvent? As in, would the chemical stores at your average uni keep it in stock?

 

[treefiddy]

That makes more sense. Although ideally you should take the measurement in the same cuvette, unless you're using matched cuvettes. Have you had a go at a commercial beer that you know the IBUs of?

Edit: still learning tapatalk so can't quote, but no it's not a commonly stocked solvent.

 

[micblair]

Matched in the sense they are both quartz rectangular cells, with equal transmittance above 200 nm, and with a 1 cm path length (which is all Beer's law cares about). The blank is placed in the reference cell holder and is comprised of an isooctane-octanol solution which I leave in the instrument over the course of the day. Some people just leave the reference cell empty though.

 

[treefiddy]

I had a bottle of Pilsner Urquell sitting around that was 3 months past its used by, so I decided to calculate its IBU with an analogous solvent that was in the lab (don't have isooctane).
My prep methods were fairly half arsed, but I calculated an IBU of 37 which is pretty close to the IBU of Pilsner Urquell (~40).

I'll buy a fresh bottle of beer with a known IBU in the next few weeks and give it another go.