Ask the Ex­perts

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Home­brew ex­pert Brad Smith, au­thor of the Beer­smith home­brew­ing soft­ware and the voice be­hind the Beer­smith pod­cast, an­swers ques­tions about wa­ter test­ing, but­tery fla­vors in beer, and leaky keg sys­tems.

Why do some of my beers have a but­tery fla­vor to them?

That but­tery fla­vor is an off-fla­vor usu­ally caused by fer­men­ta­tion prob­lems. It is cre­ated by a com­pound called di­acetyl, which is a by-prod­uct of fer­men­ta­tion. Di­acetyl can pro­duce a fla­vor like but­tered pop­corn or a slightly but­ter­scotch fla­vor­ing.

Di­acetyl is one of two ma­jor vic­i­nal dike­tones (VDKS) pro­duced dur­ing fer­men­ta­tion. The other is pen­tane­dione, which has a honey fla­vor to it. Both are present in all beers, although usu­ally they are well be­low the thresh­old where they can be de­tected. Lighter ales and lagers are more sus­cep­ti­ble to di­acetyl prob­lems sim­ply be­cause the com­pound is eas­ier to de­tect in a light-fla­vored beer.

Di­acetyl is pro­duced dur­ing ac­tive fer­men­ta­tion, but yeast can ac­tu­ally mop up di­acetyl dur­ing the later phases of fer­men­ta­tion. To aid yeast in clean­ing up di­acetyl, it is im­por­tant that you do a di­acetyl rest, which in­volves rais­ing the tem­per­a­ture of the fin­ished beer by a few de­grees at the end of fer­men­ta­tion. This can be done with both ales and lagers, and a healthy yeast pop­u­la­tion can clean up di­acetyl in as lit­tle as a few hours, although usu­ally the di­acetyl rest is main­tained for a day or two.

A healthy yeast pop­u­la­tion is crit­i­cal for man­ag­ing di­acetyl as well as other off-fla­vors, so you should make sure you pitch enough healthy yeast, aer­ate your wort be­fore pitch­ing the yeast, and man­age your fer­men­ta­tion tem­per­a­tures. It is also com­mon with some lagers to pitch ad­di­tional yeast dur­ing the di­acetyl rest to aid in mop­ping up any re­main­ing di­acetyl.

In ad­di­tion, both bac­te­rial in­fec­tion and oxy­gen can cause di­acetyl prob­lems in your beer, so proper san­i­ta­tion is crit­i­cal. You also need to min­i­mize oxy­gen ex­po­sure once fer­men­ta­tion has started as oxy­gen can cause a va­ri­ety of off-fla­vor and sta­bil­ity is­sues. It is also com­mon to have di­acetyl form in dirty keg lines and taps where both oxy­gen and bac­te­ria are present. This is a big prob­lem at many craft brew­eries and pubs, so it is im­por­tant that keg lines and taps be cleaned reg­u­larly.

What is the best way to get my wa­ter tested for beer brew­ing?

Wa­ter, which makes up more than 90 per­cent of beer, is very im­por­tant for beer brew­ing. It’s so im­por­tant that many com­mer­cial brew­ers se­lect brew­ery lo­ca­tions specif­i­cally for the wa­ter.

For brew­ing, you are pri­mar­ily con­cerned about the “big six” wa­ter ions: cal­cium, mag­ne­sium, sul­fate, sodium, chlo­ride, and bi­car­bon­ates. In ad­di­tion, a ph mea­sure­ment is handy—though not re­quired—and of­ten you can es­ti­mate bi­car­bon­ates if you have the to­tal al­ka­lin­ity mea­sure­ment. Once you have these num­bers, you can put them into your brew­ing soft­ware or spread­sheet to aid in es­ti­mat­ing mash ph and acid ad­just­ments and to match other wa­ters us­ing salts.

In some cases, you can get these mea­sure­ments from your wa­ter provider, although un­for­tu­nately, many of the pub­lished wa­ter re­ports don’t have all of the ions listed. An­other op­tion is to send your wa­ter to a lab and have it mea­sured there. Some labs, such as Ward Lab­o­ra­to­ries, can mea­sure a sam­ple for less than $30, which is a great op­tion if you have a con­sis­tent wa­ter source and need to make only a sin­gle mea­sure­ment. When choos­ing a lab, make sure you get a “brew­ing wa­ter test” and not a reg­u­lar wa­ter test be­cause many reg­u­lar wa­ter tests do not in­clude the “big six” ions.

Some wa­ter sources change over time be­cause some mu­nic­i­pal wa­ter plants pull wa­ter from dif­fer­ent sources dur­ing the year. If you need re­peated wa­ter mea­sure­ments, you may want to con­sider a wa­ter test kit, which costs a bit more than a sin­gle lab test. Wa­ter test kits are also great op­tions if you can get a group of brew­ers to share the cost or per­haps buy one through your brew club. Com­pa­nies such as In­dus­trial Test Sys­tems, Lamotte, and oth­ers have af­ford­able test kits de­signed specif­i­cally for brew­ing use. These are the kits you should look for to make sure you can mea­sure the “big six” ions. Many also have an op­tional ph me­ter you can pur­chase with the kit for ph mea­sure­ment, which can also be used for mea­sur­ing mash ph.

A fi­nal op­tion if your wa­ter sup­ply is in­con­sis­tent or re­ally not ap­pro­pri­ate for brew­ing is to sim­ply use dis­tilled or re­verse-os­mo­sis (RO) wa­ter, which has zero min­eral con­tent, and add some salts to bring the wa­ter up to the de­sired ion con­tent. This is ob­vi­ously more ex­pen­sive since you need to pur­chase dis­tilled or RO wa­ter for brew­ing, but it is a good op­tion if your wa­ter sup­ply is poor or changes of­ten.

I as­sem­bled a new keg sys­tem, and it has a slow leak as it drained my en­tire CO2 tank. How can I find the leak?

It can be quite mad­den­ing to as­sem­ble a new keg sys­tem only to have your CO tank empty out over a pe­riod of days or weeks. Even a small leak can cause CO2 loss over time, even­tu­ally drain­ing your tank. Here are a few of the steps I take when set­ting up a new keg sys­tem.

First, I care­fully check all of the con­nec­tions to make sure the hose clamps are tight and seal well. It is not un­com­mon for new keg con­nec­tors or taps to be a bit loose. For the kegs them­selves, I pre­fer to use a bit of keg lube on the posts. Keg lube, which you can pur­chase from your home­brew store, is a food-safe lu­bri­cant that pro­vides a nice seal in the event your keg con­nec­tors are not a per­fect seal. It is not a bad idea to check the rub­ber keg seals and seals on the keg posts as well as the pop­pet valves on the keg posts to make sure these are in good con­di­tion, as a leak on the out­put side can cre­ate quite a mess as beer pours from your pres­sur­ized keg.

Next I per­form a leak check. To do this, I pre­fer us­ing a large glass con­tainer, such as a clear bowl. Put wa­ter in the bowl and then very gen­tly add some dish soap or, al­ter­nately, mix in some Star San. Soap works well, but it needs to be rinsed well be­cause soap can re­duce head re­ten­tion in beer. Star San works well be­cause it will foam when the CO2 bub­bles through it but does not need to be rinsed.

Put the sys­tem un­der pres­sure and then check each of the keg con­nec­tors by im­mers­ing it in your bowl and watch­ing for bub­bles. Do the same with as many of the other con­nec­tors as you can rea­son­ably im­merse. If you have con­nec­tions that can’t be im­mersed, you can spray or drip some wa­ter or Star San onto the seals and look for bub­bling.

An­other trick is to dis­con­nect your beer kegs and up the pres­sure on the sys­tem to roughly twice the nor­mal op­er­at­ing pres­sure and check again for leaks. Of­ten you will find leaks at the higher pres­sure that might be hard to de­tect at low pres­sure. Re­mem­ber to turn the pres­sure down again and bleed off the ex­cess CO2 be­fore con­nect­ing your kegs again. This is found for iso­lat­ing the best method I have leaks.

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