Ask the Experts

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.