Day 199

Chronologically speaking, one-third of the way to the finish line; scholastically, almost half way there.

In Sensory Evaluation today, Mark Benzaquen subjected us to two “triangle tests”. We were given three samples of beer. Two samples were identical, one had been spiked with an off-flavour in about the concentration you would expect to find in a real beer. Our job was to identify the odd sample, and then try to identify the off flavour.

I successfully identified both odd samples, but only identified “metallic” as the off-flavour in the second sample. (DMS in the first sample eluded me.)

Then Mark tried a threshold test, spiking four samples of beer with increasing amounts of a sour vinegar flavour–50 parts per million, then 100 parts per million, 200 ppm and 400 ppm. Our job was to identify in which sample we detected something not quite right, and then the sample in which we could positively identify the off flavour. This would define our detection threshold and identification threshold for that flavour.

Turns out that with acetic sourness, I can detect something wrong at 100 ppm, and can identify the fault at 200 ppm. (That’s probably about average.) Yes, I also tasted the beer with the very high concentration of 400 ppm. Gnurk! Imagine adding vinegar to your beer. It wasn’t a pleasant experience.

Our tasting finished for the day, Mark then gave a lecture on some of the microbiological contaminants that can be found in the brewery, and the off flavours they can produce.

On to Microbiology, and an examination of the various ways raw ingredients can bring microorganisms to the table–barley can be infected with fusarium head blight, for instance, which will cause the barley to produce oxalic acid, which in turn will cause both haze and gushing. Water can be a huge source of microorganisms–they can even hide away in an activated carbon filter–and yeast can be contaminated with bacteria and wild yeast.

On to a closer look at the principle organisms responsible for a lot of grief at a brewery, under what conditions they thrive, and what off-flavours they produce.

Time for Chemistry. Mark reviewed some of the material from yesterday’s lecture concerning hazes, then moved on to beer carbonation. Remember the gas laws we had fun with on Tuesday–putting balloons in the freezer, and opening hot cans of Coke? Well , it was time to learn the theory behind our experiments, and so followed a review of the various gas laws that affect the brewer. (I say “review” because we already have had a fairly exhaustive look at gas laws in Packaging.) We then looked at the various ways of carbonating beer, and their advantages and disadvantages.

Weekend time. Another four assignments to work on, a presentation to begin, and exams only three weeks away…

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