When Good Beer Goes Bad

Craft Beer & Brewing Magazine - - Inside The Brewhouse - By Jamie Bogner

There are myr­iad ways for oth­er­wise great beer to de­velop un­wanted fla­vors, de­spite the best ef­forts of the brew­ers mak­ing it. Lab test­ing gives brew­ers tools to iden­tify po­ten­tial spoil­ers at a num­ber of points in the brewing process, yet still beers that don’t al­ways meet the ex­pec­ta­tions of con­sumer or brewer make it to mar­ket. Why? The an­swer is sim­ple, yet more com­plex than you might think.


that didn’t taste quite right. Maybe it was notes of tart cher­ries, or a touch of movie-the­ater but­tered pop­corn, or an ex­u­ber­ant car­bon­a­tion that over­flowed the glass that raised ques­tions in our minds as to whether this was the way we should be ex­pe­ri­enc­ing the beer. But some­thing just wasn’t right.

The bad news for beer fans ev­ery­where is that the things that turn good beer to bad—bac­te­ria such as Lac­to­bacil­lus and Pe­dio­coc­cus, wild Sac­cha­romyces yeast strains, funky Bret­tanomyces yeast, and sim­i­lar mi­crobes—are ab­so­lutely ev­ery­where in our hu­man en­vi­ron­ment. Sci­en­tists es­ti­mate that within our bod­ies alone, about 100 tril­lion mi­crobes—bac­te­ria, yeast, viruses, etc.—live and thrive. Many pro­vide ben­e­fi­cial ef­fects, as Lac­to­bacil­lus in par­tic­u­lar is an im­por­tant part of the gut biome and aids in di­ges­tion. But those same bac­te­ria are also highly ef­fi­cient at con­sum­ing the sug­ars within beer and con­vert­ing them into fla­vors that brew­ers ei­ther em­brace (in the case of sour and wild beer) or de­spise (in ev­ery other style of beer).

Given the in­cred­i­ble num­ber of these mi­crobes in our gen­eral en­vi­ron­ment, brew­ers ev­ery­where work hard to con­trol and cor­ral them with clean­ing and san­i­tiz­ing pro­cesses de­signed to knock down their num­bers. Once yeast pro­duces al­co­hol, the en­vi­ron­ment within beer be­comes even less hos­pitable for po­ten­tial spoil­ers. Yet still, some slip through in large enough quan­ti­ties to es­tab­lish a foothold. Let’s dig into why and how some of these spoil­ers are able to evade even some of the most ag­gres­sive san­i­ta­tion and test­ing reg­i­mens in the in­dus­try.

Raw In­gre­di­ents as Vec­tors

We may have a men­tal pic­ture of hops, grain, and yeast as “clean” in­gre­di­ents, but the mi­cro­bial re­al­ity of these fun­da­men­tal in­gre­di­ents is any­thing but. Hops pos­sess nat­u­ral an­timi­cro­bial prop­er­ties that

dis­cour­age growth, but some bac­te­ria still ride along with the green cones, which is why brew­ers for cen­turies have added them to beer while boil­ing.

The growth of dry hop­ping as a brewing tech­nique (adding hops cones, pel­lets, or pow­der di­rectly to fer­ment­ing or al­readyfer­mented beer) has led to more po­ten­tial for rogue mi­crobes to gain a foothold, but the an­timi­cro­bial prop­er­ties of the hops them­selves com­bined with the mas­sive quan­ti­ties of hops used tends to min­i­mize the dan­ger of cre­at­ing in­fec­tion this way.

Malted grain, how­ever, brings all sorts of po­ten­tial beer spoil­ers into the brew­house. Lac­to­bacil­lus lives in sig­nif­i­cant quan­ti­ties on the husks of malted bar­ley, so much so that many brew­eries cre­ate ket­tle-soured beer us­ing those nat­u­rally oc­cur­ring bac­te­ria. Once again, the boil­ing process on the hot side of brewing kills off any liv­ing bac­te­ria, ster­il­iz­ing the wort be­fore it’s cooled and fer­mented.

Yeast from com­mer­cial providers is typ­i­cally tested for pu­rity and po­ten­tial spoil­ers, but even the big­gest yeast providers have is­sues from time to time with rogue bac­te­ria and yeast in­fil­trat­ing their pitches of sin­gle strains. In ad­di­tion, most com­mer­cial brew­eries har­vest and re-pitch yeast, and while many test that yeast for pu­rity, cell count, and vi­a­bil­ity, there are a num­ber of spoil­ers that may ex­ist among the “good” yeast cells in small enough num­bers so as not to be vis­i­ble to nor­mal test­ing.

Wooden Bar­rels—a Cesspool of Mi­cro­bial Ac­tiv­ity

Many of us love bar­rel-aged beers, but the very thing that makes bar­rels great is also the thing that makes them a dan­ger­ous place to con­di­tion and age beer. Their per­me­abil­ity to oxy­gen al­lows for a gen­tle, con­trolled ox­i­da­tion, and the pores in the wood al­low for in­creased sur­face area for beer to ex­tract ben­e­fi­cial fla­vors such as vanillin and tan­nin in ad­di­tion to any la­tent spir­its char­ac­ter soaked into the oak. But those same pores also pro­vide a per­fect breed­ing ground for bac­te­ria and wild yeast, and in the ab­sence of strong al­co­hols to kill them, those bac­te­ria can thrive. As a re­sult, all bar­rel-aged beer— whether “clean” or in­ten­tion­ally sour—is “in­fected” to some de­gree. All of it.

Many brew­ers who pro­duce “clean” bar­rel-aged beer test the bar­rels be­fore they blend them to­gether in a bright tank. That test­ing first can con­sist of plat­ing sam­ples from the bar­rel on me­dia se­lected to ac­cel­er­ate the growth of Lac­to­bacil­lus and other spoil­ers. If colonies form, the lab knows that some­thing is grow­ing in there and can work to iden­tify it. That choice of me­dia can make a huge dif­fer­ence, though, as Goose Is­land learned in 2015. They plated all of the bar­rels of Bour­bon County Brand Stout and Bour­bon County Bar­ley­wine that year but used me­dia that did not fos­ter quick growth of a par­tic­u­larly slow-grow­ing al­co­hol-tol­er­ant Lac­to­bacil­lus strain. The re­sult was a wide­spread and very ex­pen­sive re­call.

At a cer­tain scale, plat­ing or oth­er­wise test­ing bar­rels can grow to be a lo­gis­ti­cal night­mare. “Our bar­rel pro­gram has grown to the size where a few years ago, we re­al­ized we couldn’t test ev­ery bar­rel,” says Avery Brewing’s Andy Parker. “And it would be point­less any­way be­cause you can’t test for ev­ery­thing. The idea of plat­ing 1,000 oak bar­rels ev­ery month would be in­sane. We did that in the be­gin­ning, back when it was 50–60 bar­rels at a time, but even then it was, in my opin­ion, in­ef­fec­tive—be­cause we could test for some things, but not ev­ery­thing.”

An­other means of test­ing is Poly­merase Chain Re­ac­tion (PCR) test­ing. This test­ing pro­to­col mea­sures DNA of var­i­ous or­gan­isms within the beer sam­ple to iden­tify po­ten­tial spoil­ers, and man­u­fac­tur­ers such as Pall Cor­po­ra­tion have de­vel­oped straight­for­ward sys­tems to iden­tify com­mon beer spoil­ers by their DNA. But that “com­mon beer spoil­ers” qual­i­fier is the

“We need to sep­a­rate the is­sue of food safety from sen­sory im­pact,” says Car­pen­ter. “We’re talking about how beer may change from a sen­sory per­spec­tive. So if I keep a tight span of con­trol over a beer [that may show the pres­ence of po­ten­tial spoil­ers], only serve it in my tap­room, have my bar­tenders and staff trained on what the beer should taste like and what we ac­cept as true-to­brand, and stay vig­i­lant that it ad­heres to our in­ter­nal stan­dards, then it is not a prob­lem. We’re not, and no one should ever be, talking about low­er­ing their food-safety stan­dards.”

key here—the cost-ef­fec­tive PCR sys­tems used by brew­eries are not open-ended sys­tems that iden­tify ev­ery­thing in the beer. Test­ing for ev­ery po­ten­tial spoiler would be im­pos­si­ble, not to men­tion that brew­ers to­day are dis­cov­er­ing new spoil­ers they didn’t know they needed to test for.


The so­lu­tion that Avery and Goose Is­land both set­tled on to en­sure that live mi­crobes wouldn’t spoil their beer is pas­teur­iza­tion.

“We have a pas­teur­izer now, and it’s a re­ally good tool for non-sour bar­rel-aged beer,” says Parker. “We now pas­teur­ize all non-sour bar­rel-aged beer, af­ter do­ing ex­ten­sive test­ing to make sure it didn’t af­fect the fla­vor of the beer. In blind sen­sory stuff, no one could tell the dif­fer­ence be­tween the pas­teur­ized and non-pas­teur­ized bar­rel-aged beer, so that made us feel con­fi­dent about it.”

Still, there are com­mon mis­con­cep­tions about pas­teur­iza­tion that need to be ad­dressed.

“Pas­teur­iza­tion is not ster­il­iza­tion,” says Jon Car­pen­ter, a Ka­thinka Labs con­sul­tant and ex­pe­ri­enced brewer who has worked­for An­heuser-busch, Dog­fish Head, Golden Road, and Alchemy & Sci­ence. “Pas­teur­iza­tion is an ap­proach de­vel­oped 150 years ago to cause a log­a­rith­mic re­duc­tion in cer­tain types of mi­crobes. No one should con­fuse the two—ster­il­iza­tion is much dif­fer­ent than pas­teur­iza­tion.”

Louis Pas­teur in the 1860s dis­cov­ered that it was un­nec­es­sary to kill all of a po­ten­tial spoiler in wine or beer and that

by tar­get­ing a spe­cific amount of time at lower lev­els of heat, you could kill enough of the spoil­ing agent that it would not pro­duce fla­vor changes within the life­span of the beer or wine. But even this doesn’t kill ev­ery ac­tive mi­crobe in a beer, and some liv­ing things still get through.

“You’ll see quite a blend [in fin­ished beer],” says Mary Burge, lab di­rec­tor for Ka­thinka Labs. “Some of the beer we test will show Sac­cha­romyces present, there’s Bret­tanomyces present, there’s Can­dida present, there’ s Zy­gos ac charomyces present. More of­ten, we see the Sac­cha­romycesCan­did able nd, be­cause Can­did a is ev­ery­where around us .”

Chang­ing Our Think­ing About “In­fec­tion”

Many who use the term “in­fec­tion” do so with­out un­der­stand­ing what it means or the im­pact it has.

“We need to sep­a­rate the is­sue of food safety from sen­sory im­pact,” says Car­pen­ter. “We’re talking about how beer may change from a sen­sory per­spec­tive. So if I keep a tight span of con­trol over a beer [that may show the pres­ence of po­ten­tial spoil­ers], only serve it in my tap­room, have my bar­tenders and staff trained on what the beer should taste like and what we ac­cept as true-to-brand, and stay vig­i­lant that it ad­heres to our in­ter­nal stan­dards, then it is not a prob­lem.

“We’re not, and no one should ever be, talking about low­er­ing their food-safety stan­dards. But when a brewer re­leases a beer in their tap­room know­ing that it has a slight anaer­o­bic mi­crobe count in it, we know what’s grow­ing in there is not un­safe for peo­ple; it might just change the fla­vor. So what we can do as con­sci­en­tious in­di­vid­u­als is make sure that the only place the beer is served is where we have con­trol to make sure that if it does change, we can stop giv­ing it to the cus­tomer.”

Mov­ing past the bi­nary con­cept of beer as “clean” or “in­fected” is one that’s im­por­tant for con­sumers. It’s not a ques­tion of whether there are things in a beer that could take the fla­vor in an un­in­tended di­rec­tion—they’re there in ev­ery beer, in­clud­ing many beers that have been pas­teur­ized. The ques­tion, rather, is how much is in there and whether that amount is enough for that mi­crobe to gain a foothold in the hos­tile al­co­holic en­vi­ron­ment?

“It’s a crazy mi­cro­bial world out there,” says Parker.

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