Day 198

Seems that we are a bit behind in Chemistry, so with only three weeks left, Mark Benzaquen gave us a supplementary chemistry lecture in place of our microbiology lab today.

First on the agenda was spectrographic analysis of flavour compounds in beer, specifically with either a spectrophotometer or with a gas spectrometer.

We actually used a spectrophotometer in the lab a couple of weeks ago to measure the amount of iso-alpha acids–the bitterness–in beer. As I recall, the machine was on strike for better working conditions that day, but the way it’s supposed to work is based on the fact that various compounds while in solution absorb light of a certain frequency. If you pass a given amount of light of a single frequency through a solution and measure how much light has been absorbed, you can calculate how much of the compound was present.

A gas spectrometer is way more expensive, but also way more cool–by analysing a compound’s affinity for a gaseous versus a solid state, it not only gives you the amount of a compound in a sample, it also provides you with a molecular “fingerprint”, allowing you to positively identify the exact compound that is present. Very CSI.

Next topic was hazes–what they are, why they occur, and how to deal with them. If you are a longtime lover of beer, you know that from time to time, a beer that should be bright and clear is hazy. Sometimes the haze only shows up when the beer is cold, and disappears when the beer warms up–chill haze. Sometimes the haze is there all the time–permanent haze. Chill haze will, with time, eventually morph into permanent haze, meaning the longer your beer sits on the store shelf, the hazier it will become. Obviously, the more you can do to reduce the compounds that cause haze, the more stable your beer will be over the long term.

(This is probably less of a concern to the brewpub owner who sells all his beer within a week of it being made, but more of a concern if your beer is going to be sitting on a store shelf under a fluorescent light at room temperature for three months. )

Beer hazes can be caused by bacterial infection (eww!), excess carbohydrates, oxalates and excess polyphenol-protein complexes. Since this was Chemistry, not Microbiology, we didn’t deal with the first one in this class.

Carbohydrate hazes are caused by excess amount of either beta-glucans or unconverted starch in your beer. Adding extra enzymes of the proper type to the mash tun should take care of the problem.

Oxalic acid is present in barley that was stressed during the growing season, and shows up in beer as a haze, caused when the oxalic acid forms a crystalline matrix. This matrix also provides a great place for CO2 micro-nucleation sites, so when you open the beer, you instantly get a gushing beer fountain that leaves half the bottle on the countertop and the other half on your clothes. The easy way to get rid of this problem is simply to add more calcium salts such as calcium sulphate to your foundation water–the calcium ions binds with the oxalic acid to form calcium oxalate, an insoluble powder better known as “beer stone” that is left behind in the mash tun.

That leaves us with polyphenols and proteins. In this case, prevention is the best way to fix the problem.

Excess polyphenols come from barley husks, and are in finished beer either because the sparge water that washed across the husks was too hot (more than 80°C), or because the wet grains were excessively raked, turned or otherwise agitated too roughly in the mash tun or lauter tun. So, sparge at 74°C, and be gentle with your grain to avoid the whole problem.

Some protein in beer is necessary–protein forms the walls of bubbles, giving the beer a nice head. Excess protein can be a problem, however. It usually comes from barley that was “undermodified” during malting–large proteins that should have been broken down into amino acid have been left intact. So avoid using undermodified grain–much easier said than done.

So what to do if you have an excessive load of polyphenols and/or proteins? You can’t filter them out, because they start as very small pieces, too small to capture in most filters. Then once the beer has left your brewery, the small pieces join together to form large pieces that cause haze.

There are several steps you can take while the beer is in the brewery:

  • Let some of the protein settle out during maturation, possibly aided by a clarifier such as isinglass (made from fish bladders).
  • Add papin (an enzyme derived from papaya) to break down proteins, then deactivate the papin via heat pasteurization (Don’t use it if you don’t pasteurize your beer–the still active papin will continue to breakdown all the protein in your beer: Goodbye, foam and head.)
  • Add tannic acid just before filtering. Proteins will bind to it and precipitate out. (However, the sediment produced can clog the bottom of your tank, making removal of the beer very slow.)
  • Add a silica gel before filtration. Proteins will bind to the gel matrices, which are then filtered out of the beer. (However, these gels are relatively expensive.)
  • For polyphenols, use PVPP, an agent that binds polyphenols to it. (However, PVPP is expensive. It can be reused, but the equipment required is expensive.)

Lunch. Then back to our lab stools for three hours of Packaging.

Today, the science of the beer bottle filler–the machinery and mechanisms used to get beer from the bright beer tank into the bottle in eight easy steps. (Pre-evacuation of air, CO2, re-evacuation of CO2 and any remaining air, pressurising with more CO2 to same head pressure as bright beer tank, beer bottle filled, pressurising with CO2 to force any excess beer back up filling tube, depressurising bottle to atmospheric pressure, and finally “snifting”–lowering bottle away from beer filler head while using a jet of CO2, a small jet of hot water or knocking the bottle to produce enough foam to displace any air in the neck of the bottle until the bottle can be capped a split second later.

Another five-hour day on a lab stool. I ain’t gonna sit down for the rest of the day, at least not without some serious padding.

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