MBAC 100th Anniversary Conference: Part 4

The second day of the MBAC Technical Conference continued with presentations about malt enzymes — pretty much a review of Kevin Somerville’s 1st-year Ingredients class, so I won’t get into it — and an overview of brewing automation. However, it was the next two presentations I found interesting.

Barrel Dwellers (Karl Ockert, MBAA Technical Director)

Karl Ockert, while brewmaster at Bridgeport Brewing in Portland, Orgeon, was in the vanguard of the barrel-aging movement. However, one of the problems with using wooden barrels is beer spoilage due to bacterial infection. Karl gave us the low-down on how to keep beer-spoiling bacteria “in check”. His thesis was that you may not be able to sterilize wood, so you can never get rid of all the exotic fauna growing in your barrel; but you can keep the nasty critters in check.

The one saving grace we brewers have is that beer is a very hostile environment for most microbes. Many bacteria rely on oxygen and thrive in an alkaline environment, around pH 8; however, beer is a fairly acidic liquid, around pH 4.2, and contains little or no oxygen. So there are only a few beer-spoiling microbes that can live in that environment:

  • acetobacter: Produces beer-souring acetic acid in an oxygen-rich environment, but can also survive with little oxygen, although it produces acetaldehydes under those conditions
  • lactobacillus: the same bug that sours milk by producing lactic and acetic acid. It is anaerobic (doesn’t require oxygen) and actually prefers a very low pH of 3.5, so it is quite happy in beer.
  • pediococcus: another anaerobic bug, this one produces lactic acid, diacetyl (butterscotch flavours), as well as ropiness and slime, so when it spoils beer, it really goes all out.
  • Brettanomyces: There are four strains of this wild yeast that all produce a hodge-podge of complex flavours (according to Karl: phenols, odours of rancid cheese, goat and baby vomit — and those are just the flavours and aromas that some brewers desire. Under the right conditions, Brett. can produce a whole host of “undesirable” flavours as well, such as mouse or rabbit urine. Don’t ask me how rancid cheese, goat and baby vomit made it onto the “desirable” list.) Under ordinary conditions, the usual yeast we use, Cerevisae, will outcompete Brett. for the simple sugars like glucose, sucrose and maltose. However, Brett. is very cunning — it simply waits until the Cerevisae has finished up all the simple sugars, then swings into action, devouring all the remaining complex sugars that the Cerevisae left behind. Brett. can actually digest cellobiose, the sugar found in wood cells, which is why once your barrel has Brett., it’s there to stay — it simply hides out in the wood until the barrel is refilled with wort.

So, how do we keep the beer spoilers in check? (Unless we want them in the beer. Yes, some brewers deliberately “inoculate” their wort with some of the above.) First Karl suggested a cleaning regime:

  1. Rinse the barrel with warm water after use
  2. Clean the barrel with a weak alkaline solution
  3. Steam the barrel or fill with hot (80C) water for 20 minutes to give a good penetration of heat deep into the wood.

Barrel maintenance includes:

  • keep the barrel continuously filled — don’t let it dry out, since the staves will shrink, allowing seams to open up
  • when you fill it, top with an inert gas to reduce oxygen content in the barrel
  • keep the bung area clean
  • if you can’t refill the barrel right away, store it wet with a solution of sulphur dioxide or citric acid
  • track each individual barrel: number of uses, and any issues that you had with it

Avoid cross-contaminatioon with other beer operations in your brewery:

  • assign specific hoses, gaskets and clamps to barrel operations, and isolate them from other equipment.
  • run barrel operations AFTER non-barrel operations, then clean and sanitize
  • use a flash pasteurizer before beer gets to the bright tank to avoid cross-contamination in the packaging line.

Karl also took a question about using whiskey barrels. Many brewers want to use these barrels to add the flavour of the whiskey to the beer. However, if the first step is to rinse out the barrel, won’t this remove most of the residual whiskey flavour? Karl replied that because whiskey barrels are probably sterile due to the whiskey’s high alcohol content, don’t rinse them the first time you use them. They are probably good for 3-4 uses before the whiskey characteristic is used up, so for subsequent uses, rinse and then refill immediately. If you want to add an extra measure againt beer spoilage, increase the number of IBUs in the beer — high hop bitterness discourages bacterial growth.

Washing Yeast with Chlorine Dioxide (George Agius, Sealed Air, and Andrew Goulds, Goulds Consulting)

Your yeast slurry can become contaminated with some of the beer spoiling bacteria mentioned above. If that happens, there are four traditional responses:

  1. Throw out the yeast and start with a fresh batch.
  2. Rinse the yeast with cold distilled water, wait for the yeast to settle, then decant off the water, which in theory will carry away the bacteria and dead yeast cells. However this method requires a lot of water and a lot of time.
  3. “Acid wash” the yeast with a low concentration of phosphoric acid. This temporarily lowers the pH of the yeast slurry to around pH 2.3, which will kill off most aerobic bacteria. However anaerobic bacteria will be more resistant, and wild yeast such as Brettanomyces will be unaffected. There is a common belief amongst brewers that once you acid wash a batch of yeast, it subsequently becomes more liable to infection; so if yeast has been acid washed once, it has to be acid washed every time.
  4. “Acid wash” the yeast as above, but add a 0.75% solution of ammonium persulphate. This will kill even low-pH resistant bacteria, but will kill off or weaken some of your yeast as well.

All of these methods have fairly large downsides, so the two authors of this paper decided to try washing the yeast with chlorine dioxide (ClO2).

Theoretically, there are some significant pros:

  • ClO2 is effective over a wide pH range (2-10)
  • unlike many other chemicals, it doesn’t attack or break down tannins in the beer, so won’t affect head retention
  • unlike simple chlorine, it does not produce carcinogenic trihalomethanes

However, there are also some significant downsides to chlorine dioxide:

  • You can’t just run down to the chemical store and buy a bottle — ClO2 has to be manufactured in situ with specialized equipment, usually requiring a strong acid such as hydrochloric acid and sodium chlorite.
  • Both ingredients are dangerous, and the chlorine dioxide, if it escapes, is toxic.

Research conducted by Agius and Goulds indicated that washing yeast with a solution of 100 ppm of ClO2 for 90 minutes resulted in bacterial counts of zero (both aerobic and anaerobic varieties), which is highly effective. However, yeast viability was reduced by 10-15% as well. The process seemed to require much less time than traditional acid washing to achieve a greater effect.

They concluded that further research was needed to determine an optimal concentration of ClO2. They also acknowledged that since 50-75 ppm of ClO2 is toxic if handled improperly, more research was needed in order  to develop a safe process.

————–

There was one more technical presentation about using double-seat valves in a fermentation tank pipe net, and a presentation by Michael “Pinball” Clemons, former CFL all-star; but with Toronto’s infamous rush hour traffic already ramping up, most of the delegates hit the road.

 

 

 

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