Day 212

Sensory Evaluation: Another harsh way to wake up the taste buds on a Friday morning, as Mark Benzaquen subjected us to head-shaking off-tastes from various non-organic sources.

First up was beer contaminated with caustic. Caustic soda (aka sodium hydroxide) is an cleaner used almost universally in breweries, since it is highly effective at cleaning organic materials off of stainless steel without affecting the metal. But let it get into your beer and the effect is very noticeable–cheesy aromas (probably an interaction with hop oils), absolutely no head (it lowers surface tension so bubbles can’t form) and a flat, watery taste with very little beer flavour. Imagine flat, bland barley soup. Yecch.

Then acid cleaners. Phosphoric acid (and occasionally nitric acid) is used to clean scale and “beer stone” haze (calcium oxalate precipitates) from stainless steel. If acid gets in beer, the aroma becomes thin and sharp, the taste is accentuated almost to the point of harshness, and at higher concentrations, there can be a sourness as well. Made me grit my teeth.

And then sanitizers used to kill bacteria in the brewery. Peracetic acid (PAA) is the popular choice at a lot of breweries because at low concentrations, it doesn’t affect beer flavour–spray it on a hose connection and you don’t have to worry about rinsing or washing it off. However, stronger concentrations are often used to sanitize vats and if any ends up in the beer, it adds vinegar to both the smell and taste. Which is to say, “Gecch!”

Thankfully Mark did not have any further ways of messing with us, although he did mention several other non-biological contaminants that can end up in beer: conveyor belt lubricant, cardboard dust from cartons, plastic tastes from old bottle crown liners, etc.

Between the thought of finding conveyor belt lubricant in my beer, and the lingering taste of vinegar on my tongue, I was almost put off the thought of having a beer at the student pub at lunch.


In Chemistry, we started with a review of hops. We had covered this topic a bit more in-depth in Kevin Somerville’s Ingredients class in the fall, but today we looked at hop components from more of a chemical point of view. Then we moved on to the chemical interactions that happen in the kettle during the kettle boil. I mean, we knew (again, from our Ingredients class) that the alpha acids in hops do absolutely no good to beer in their native form, since they are non-soluble, and will simply float to the bottom of the vat. However, boil them for about 60 minutes at 100°C and they will be isomerized–their chemical structure changed so that they readily dissolve in water (and beer), ready to share their hoppy goodness with you and I.

However, the boil is also important in other ways:

  • The kettle is where now-useless enzymes, proteins and polyphenols clump together and fall out of the wort–the hot break.
  • Excess water is evaporated off, raising the concentration of sugars.
  • Beer takes on a darker colour due to Maillard reactions.
  • Oxygen scavenger compounds known as reductones are formed which will help to reduce oxygen counts in the wort
  • The pH of the wort drops, making it a homier place for yeast.
  • And dimethyl sulphate (DMS), author of cooked vegetable flavours in beer, is quickly and quietly wafted to the heavens.

Those are some of the chemical reactions during the boil, but there are also some microbiological effects in the kettle. However, our microbiology class was cancelled (since most of the class had departed for an end-of-the-term pub crawl in Buffalo), so we’ll have to wait for our final class next week to find out more.


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