“It doesn’t taste like what we wanted it to” was the quote used at a recall of a Bourbon-barrel aged beer that was infected with alcohol-tolerant Lactobacillus acetotolerans, a souring bacteria.

American brewers have pushed boundaries of traditional brewing with the development of barrel-aged beers, with previously-used wine barrels, bourbon and sprits barrels, and with installation of foeders (wooden beer tanks) in their cellars. Beers no one imagined 20 years ago are finding their fans and making names for the breweries that produce them.

Over 100 years ago, it was only the British who used unpitched wooden beer casks, and the special flavors of Brettanomyces were prominent in many ales of the times. In continental Europe and in North America, the use of pitched beer casks, (casks lined with a flamed-on resin) (a kind of natural plastic with a very mild taste and aroma),  prevented beer from contacting wood and offered a smooth and cleanable surface.

Spirits casks expose the contents to direct wood surface contact. The uneven surfaces and spaces (pores within the wood) offer surfaces for microbial adhesion and colony growth. And with the fact that the surfaces are no longer flooded under spirits, one expects to find species including Zymomonas, Acetic acid bacteria, Candida, Zygosaccharomyces etc. present. 

Even typical ‘gut’ bacteria are favored by high concentrations of potential prebiotic components like arabinoxylan, beta-glucan and Maillard products like melanoidins (1). And many brewers these days have opened Pandora’s box for wild inoculations and spontaneous fermentation processes that allow them to express their terroir… microbes represent the new terroir.

Oak barrels are porous and air and microbes can be transported in and out. And the number of breweries using open-top coolships to cool wort in their brewhouses is impressive.

It should be clear that putting any beer, even if high-alcohol and high-hopped, in a cask and ageing it inside the cask, will inevitably bring microbiological challenges. Brewers are taught well on the antimicrobial properties of hops, but a second style of beer presents new microbiological challenges…

The growth of dry hopping as a brewing technique (adding hops cones, pellets, or powder directly to fermenting or already- fermented beer) naturally leads to rogue microbes gaining a new foothold in bulk beer.

Belgian brewers flavor their lambics with cherries and raspberries to make kriek and framboise, and these classic styles served as inspiration for countless North American breweries. Innovative beverages based on natural cereal and berry products have gained consumer attention and may open new opportunities for the breweries.

And the now-common practice of including loads of fruit in beers to deliver special flavors increases opportunity for undesired microbes to enter precious beer, often via species found on the skins of fruits. “Fruit” is a broad term with so much variety and also the form of the fruit. It is not uncommon for American breweries to add 8-25 lbs of fruit per barrel, and quite frequently, the addition is on the cold side.

Saccharomyces cerevisiae var. diastaticus is a natural variant of brewer’s yeast Saccharomyces cerevisiae. While cultured yeasts are essential for beer production, wild yeasts including S. diastaticus allow for a secondary fermentation in tank or in final package. Other wild yeast species of concern include Debaromyces, Brettanomyces Dekkera, Pichia, Hanseniaspora, Kluyveromyces, Torulaspora, Williopsis (2). And different fruits can bring in mycotoxins such as Ochratoxin A and Patulin (3).

Yeasts and vegetative cells of bacteria are typically very sensitive to heat; Yeast D-values (an indication of death rate) rarely exceed 1 min at 55 °C…but Shearer et al. (2002) did find a S. cerevisiae showing D values of 13 s at 71.1 °C in apple juice. Yeasts and vegetative cells of bacteria are typically very sensitive to heat (Stratford 2006). Yeast D-values rarely exceed 1 min at 55 °C.

Vegetative cells of beverage-spoiling microbes are usually more thermotolerant than bacterial pathogens or protozoans (Tribst et al. 2009, Lawlor et al. 2009). Shearer et al. (2002) found S. cerevisiae showing D values of 13 s at 71.1 °C in apple juice. Yeast ascospores can have 30–350 x higher thermotolerance compared to vegetative cells.

For example, D60 °C values of 7–22 min have been reported for asci of S. cerevisiae (3). A heat resistant Pediococcus sp. required 16 s heating at 71.1 °C for 5-log reduction in a simulated apple cider (Piyasena et al. 2003). Pasteurization treatments used in the beverage industry are usually sufficient to inactivate all species of concern, and most enzymes which otherwise could be adding fermentable sugars into the packaged product over time.

Many things occurring in the brewing processes are not 100% under control of the professionals. Packaging is. There is a mission-critical component within packaging that serves as our last layer of protection on beer that will soon leave to the wide world.

By virtue of applying heat within the contents of the already-sealed can or bottle, a PRO Pasteurizer is a proven means to offer long-term shelf-life stability with no impact on integrity of the package. A gentle passage under the water sprays in the pasteurizer, controlled heating in the PRO Single Zone Batch Pasteurizer or heating, then cooling in the PRO Triple Zone Batch Pasteurizer or a PRO Tunnel Pasteurizer, of the individual package contents… can result in confidence and security in the packaged beer.

As breweries in the USA increasingly move from the traditional can liners to ‘BPA- non-detectable’ materials applied to can interiors at their manufacturing plants by waterborne styrene-acrylic spray, waterborne non-BPA epoxy spray, or waterborne polyolefin dispersion spray, there have been no indications of de-laminations so adherence is the same as existing, proven liners.

And though it is true that sleeved cans (where a ‘brite’ (or unpainted can has its label heat-shrunk on the can body)  does temporarily ‘relax’ while the can is in the pasteurizing zone, this author has seen many examples where there is no evidence of any concern, no occurrence of water bubbles under the sleeve… but it can occur so prudence in qualifying sleeved cans from the sleeving service providers out there is called for.

Authored by Jaime Jurado

Past President-MBAA(Master Brewers Association of the Americas)

Article References: 

  1. https://lib.ugent.be/fulltxt/RUG01/002/482/227/RUG01-002482227_2018_0001_AC.pdf
  2. http://nik.waszczak.com/wp-content/uploads/2015/04/Microbiological-stability-of-beer.pdf
  3. https://www.vtt.fi/inf/pdf/tiedotteet/2011/T2599.pdf

PRO Engineering and Manufacturing was established in 1977 by Ed and Dave Michalski as a steel fabrication shop. For more than 40 years, PRO Engineering and Manufacturing, Inc. has been delivering solutions for beverage product shelf stability and consumption safety. As leading innovators in post-fill pasteurization, our skilled team offers the best in high-quality pasteurization equipment.

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