Beer Forum

I probably spend way too much time on homebrewing, and I figure I'm big enough of a nerd to care about the results; so I dropped some cash and sent two beers away for White Labs Big QC Day this year. I sent in a Koelsch that I really liked and a batch of North Oakland Double IPA that was really good, but I thought might have some diacetyl issues. The idea was to send in one really big, high alcohol beer that was a little rough around the edges, and one super clean, light beer with no detectable flaws. Both had done well in competition, so this was a way of getting some other objective information about the beers & brewing process.

Here are the results:

http://destroy.net/brewing/461/461-bigQC-2009.jpg

Background information from White Labs here:
http://www.whitelabs.com/qcday-2009.html

And the original recipes of the two samples I sent:

http://destroy.net/brewing/461/461_double_IPA_2008.html
http://destroy.net/brewing/461/461_Kolsch.html

** Feel free to read this next section imagining the nerdy lisp voice
A couple observations. First off, I was pretty thrilled to see zero wild yeast, aerobic or anerobic bacteria in the samples. Ok, so the IPA definitely had diacetyl above the flavor threshold (100+ppb). Interesting that the IPA showed up as 29IBU (way off from the "calculated" value in the recipe), not to think that the measuring accuracy was off because the Koelsch hit 18 IBU in the analysis while pro mash calculated that one at 19.6. Not bad. In both cases the actual FG came back 2-3 points lower than what I was measuring, and the increased alcohol to match. A pretty good indication that the home hydrometer is reading on the high side at the low end of its scale. Interesting stuff. I'd highly recommend doing the big QC Day if you're interested in this sort of geeked out stats.. Cheers,



-Nathan

That IBU number for the double IPA seems way low. Do you think that by judging the flavor of the beer you would have guessed it higher than the test indicated. It makes me wonder about the "real" IBU numbers that we are all getting because I don't normally add near as many hops as you, especially higher alphas for bittering, and I have been thinking my IBUs were much higher than that. Shows how accurate Promash and the other programs are at predicting actual IBU.

Chris

The double IPA tasted much hoppier than 29IBU. I would estimate by taste that it seemed in the 70-80 range. It is interesting that the isomerized bitterness from the 90 & 45 minute hop additions comes to 42 IBU.. It could be that lots of late hopping doesn't really isomerize very well and doesn't come across as IBU in a lab test such as this. It is still a bit of a mystery though.

I read this post and was fairly interested in this and took a look at White Labs analytical methods. Here are a couple of notes on the science side of things:

nahthan wrote:
Ok, so the IPA definitely had diacetyl above the flavor threshold (100+ppb).

Not to throw White Labs under the bus or anything but I don't like the way they analzyed this (and quoted you to such accuracy). Headspace Gas Chromatograph (GC) injections introduce a lot of internal fluctuation. Not being familiar with this exact equipment model, a normal GC displays on average 10 % RSD on injections. Headspace is 20-25 % RSD. I expect that they use internal standards and things to fix this but I still have never worked with any headspace methods that display that much accuracy. Also, a large part of my job currently is to test for diacetyl by GC (not using headspace injections). Analysis is difficult due to a lot of interactions with diacetyl and internal instrument components. Your approach to this seems to be a good way to interpret this data i.e. Yes, diacetyl is in there in relatively high quantities but the specific quantity is not really reliable. (I guess I just disagree with them reporting it with an actual value and not a true/false type report or at least only report it to 2 sig figs not 4).

nahthan wrote:Interesting that the IPA showed up as 29IBU (way off from the "calculated" value in the recipe), not to think that the measuring accuracy was off because the Koelsch hit 18 IBU in the analysis while pro mash calculated that one at 19.6.

Again, not to throw White Wabs under the bus but this is a little suspiscious. Quantitative photoanalysis on photoreactive chemicals is very difficult. Basically what they did was shine a light through the samples and read how much light is absorbed by your sample. If if the process of shipping, sample receiving by the lab, sample prep, or pre-analysis, these samples were exposed to light, the photocatalytic reactions would begin. This means that there would be less absortion during analysis and cause a much lower reading than expected. Did you send your expected values in with your samples? I would think that if they knew what you were expecting it to be they would have investigated these numbers a bit. That's the problem with contract lab work is sometimes you get bad results and you just don't know.

Anyway, I hope this gives you a little insight into your data. Keep in mind I might be wrong with this since I don't know White Labs specific methods. I do know analytical chemistry though so those would be my general areas of concern.

Hey there BrewChemist,
Thanks for weighing in as a professional, I am most definitely not trained in this area.
The expected values are all of my own based on my own calculations through promash, White Labs didn't ask for any of that data. The IPA sample could have easily been exposed to light along the way somewhere, although I took great care to minimize that during the time that I had it. I think the spirit of the big QC day is to give individual brewers a snapshot into what might be happening on a GC analysis level to compliment organoleptic analysis, and on that level I think it succeeded. Any further investigation would be an exercise left up to the brewer/brewery. You make a good point though, all lab analysis has a margin of error and it's not always a good idea to read too much into one number from one test.

thats pretty cool - do it a few more times and you can probably come up with some correction factors for your system on Promash