Curing Sparging Woes, Talking Oxidation, and the Subtleties of Beer Gas
Q
I have been making a pumpkin ale for the last 7–8 years. Because I put flaked oats into the grain bill, I have always used rice hulls to prevent a stuck sparge; however, 3 out of the last 4 batches, my first runnings and sparge have been very slow. During my last batch, it took an hour to get almost 2.5 gallons (9.5 L) using 7 gallons (26.5 L) of strike water. I sparged with another 5–6 gallons (19–23 L) of water and it took almost an hour to collect as much as I could. In the past, it has taken longer than other styles to collect wort but not this long. Could I possibly be using too many rice hulls on the bottom of my mash tun? I put the rice hulls on top of my false bottom and mix into the grains. I use a 10-gallon (38-L) water cooler as my mash tun.
Grain bill: Pale malt, Caramunich® malt, Munich malt, caramel 40L, flaked oats, white wheat malt, and Victory® malt for a total of about 13 pounds (5.9 kg) for A 5-gallon (19-L) batch. My last batch was double. I also put about 30 ounces (850 g) of canned pumpkin in the mash.
Mark Connell
Bedford, Massachusetts
A
The likely culprit to this problem, assuming that you have been using the same basic recipe over the last 7–8 years, is beta-glucan from the flaked oats. I am betting on this ingredient because the problem you describe is typical for how high-molecular weight beta-glucan gums associated with certain grains, most notably unmalted oats, rye, wheat, and barley, affect wort recovery. But why now?
There are so many things about brewing raw materials that can cause brewers headaches because our raw materials are inherently inconsistent. Crop variability can be classified into two big buckets; variability due to genetics and/or variability due to environment. Or, in the parlance of geneticists, G x E influences. Even when brewers select/purchase specific varieties of barley, for example, there is still considerable variability within and between crop years based on environmental variables such as growing region, temperature, rainfall, farming techniques, and harvest conditions. Add to this the different ways that cereal grains are processed and the permutations become huge.
So why am I focusing on the unmalted oats in your recipe? For starters, oats are a great source of beta-glucan gums that slow wort collection. The other reason is that the oats are the one “generic” ingredient in your grain bill. While oat variety and processing nuances, such as flake thickness and flaking conditions, can have a real influence on how oats perform in the mash, most brewers, including most commercial brewers, know very little about the flaked oats purchased for brewing.
Using rice hulls is a good start to warding off wort collection issues associated with troublesome ingredients, like oats, but may not be enough for particularly gummy lots. The addition of beta-glucanase to the mash is an option that has increasingly become more common as the popularity of hazy IPAs continues to grow and brewers are exploring ways to minimize the bumps that come with using unmalted grains. And as a continuation of this approach, the use of malted oats, both naked and fully clothed (with hull), is also on the rise. The next time you brew this beer or another beer with oats, consider using a different flaked oat, adding beta-glucanase and a respective rest to the mash, and/or subbing malted oats for some or all of the flaked oats. Hopefully one of these suggestions works and you will not have to turn to Plan B; smashing pumpkins.
Follow-up to previous answer: I answered a question from Scot in Chicago, Illinois that was published in the November 2019 edition of BYO. His question was about hop fade and why some of his recent New England IPAs lost hop aroma quickly after packaging. Scot let me know in his question that he was a very experienced brewer. Knowing that biased my answer because I did not think that he suddenly had a rash of oxidation problems. His question had me publicly scratching my head. Thanks to emails from Karl Helmstetter and Joe Walts (below), I now offer some more insight into the possible causes of hop fade.
Q
I really enjoyed your answer to Scot’s question about hop fade, especially your honesty as an author and brewing expert. It’s always easier for me to believe and accept people’s answers when they acknowledge their own bias or limitations, even when those come from the questioner!
I had a thought regarding Scot’s situation; he said he cold crashes in the carboy, hops are bright when added, faded a week later. If he is cold crashing without a CO2 source, suck-back could easily add more than enough O2 to dull the hops, and hazy IPAs are especially sensitive to this. No way to know without more information, but does this seem possible?
Karl Helmstetter
Charlottesville, Virginia
Q
I was catching up on brewing magazines this morning, and I came across your Mr. Wizard response to a question about fading hop character — which got me thinking: Could the problem be related to either oxygen pickup during kegging, or migration of hop aroma into a too-large (and increasing over time) headspace in the keg?
On the oxidation front, I would not expect this to be an issue for two experienced brewers. However, maybe something unexpected happened such as a loose hose/tube connection or even a low-purity CO2 cylinder. And the fact that they cold crash prior to packaging could cause all kinds of problems if they don’t apply headspace pressure beforehand.
On the headspace front, it would be interesting for the brewers to package one batch in a keg and one batch in bottles to see how they compare over time — but the addition of bottle conditioning could create an unfair advantage in terms of oxygen reduction and possibly even biotransformation. Even without this investigation, maybe the brewers simply had a few low-yielding batches that accelerated their normal hop fade.
Joe Walts
Octopi Brewing Company
Madison, Wisconsin
These emails are great and give me a little more fuel to expend on the topic of hop fade. For starters, as someone who really dislikes oxidized beer, why did I not consider oxidation as a possible cause of the problem? I dismissed oxidation as the probable cause because of Scot’s experience. That is what is called a really bad assumption.
In the world of commercial brewing, brewers are obsessive about minimizing oxygen pick-up because oxygen quickly ruins beer. Even low concentrations of this potent molecule have a marked effect on reducing beer shelf life. Over the last 20 years or so, two technological changes have really been a game-changer when it comes to the general topic of oxidized beer. The first is the development of low-speed packaging lines that have dramatically reduced total package oxygen (TPO) in cans and bottles to levels that are on par with the fanciest, high-speed lines used by the largest brewers. The second real game changer is with dissolved oxygen (DO) meters. Today, DO meters are reliable, accurate, and widely used by brewers of all sizes (although not all breweries own these spendy instruments). Joe’s reply about leaks and gas purity comes from his experience in commercial brewing where brewing problems almost always include a question about equipment or raw materials . . . as in, what mechanical failure or out-of-spec [insert ingredient here] caused this problem? And Karl’s question about suck-back is in the same vein of the original inquiry.
Let’s start with suck-back. This happens when liquid from an airlock is sucked into the container it is intended to protect from the environment when the container headspace is cooled and a vacuum is formed. That sucks! And for a couple of reasons. One reason is that the airlock may contain “stuff” in the liquid barrier, such as microbes, cheap vodka, or bleach, that does not belong in beer. Even if the airlock contains nothing but pristine water, it offers no protection from the environment when empty. Picture a carboy that was bubbling slowly after primary fermentation. If a sample could be taken from the beer and the headspace and measured, there would be very little if any DO in the beer and in the headspace.
The second reason that suck-back sucks is air. Once the airlock has been gulped into the carboy, the headspace picks up oxygen from the environment, and headspace oxygen then enters the beer. A fallacy about carbon dioxide headspaces is that the density of the carbon dioxide protects the beer beneath. While a carbon dioxide gas blanket, especially during fermentation when the blanket is constantly flowing up and out of the fermenter, do help protect beer from oxygen, the blanket is not immune from gas mixing. Pesky principles like gas diffusion, convection, and Brownian motion work 24-7. An empty airlock needs to be re-filled pronto, and a full airlock is preferably never sucked into a carboy!
Joe’s approach to this problem is open-ended and questions everything involving beer handling that can result in an increase in DO. A DO-meter-wielding commercial brewery experiencing hop fade and suspecting oxygen would be on this by methodically measuring beer DO before and after transfers, during storage, and right before packaging. After packaging, quality control (QC) pros vigorously shake packages to equilibrate sample headspaces with the beer before measuring TPO because inquiring minds want to know!
The point is that there are numerous, and often times invisible, sources of DO. Leaky gaskets, pump seals, and valve seats, DO in push water, low-purity carbon dioxide, vacuum pump failures (used on package lines for pre-evacuation before filling), inconsistent fobbing before capping, poorly purged bright beer tanks/kegs, below normal fill levels in tanks, and loose hose clamps can all lead to increases in DO.
The below-normal fill level is an interesting problem that can affect oxidation and/or aroma partitioning. Large headspaces contain more gas, and a headspace of a given oxygen content is less problematic when the headspace is small, for example in a normally-filled bottle or can. But large headspaces also provide a big, aroma-devoid gas space where aromas in beer can equilibrate.
Q
I read the article on serving stouts with beer gas on your website (https://byo.com/article/nitrogen-stout-faucets/), and I’m hoping you have some insight into a situation I’m having. I recently added a beer gas line and a stout faucet to my home kegerator. I got a Keg of Belching Beaver Peanut Butter Milk Stout from a local store. The beer comes out very, very foamy during pouring, but the head disappears completely after a minute or two and then the beer is flat. In the aforementioned article, it describes a period of time for conditioning a keg on beer gas. I guess my primary question is: Is this step typical for a commercial keg or is that step normally only homebrew? Do all commercial kegs for nitro stouts need to be conditioned over a week like this? Any insights you have would be helpful and appreciated.
Bobby Smallman
San Francisco, California
Years ago I was talking to a crusty dude named Larry who worked for a local beer distributor about the dirty draft beer tricks that can be played by competing distributors. Larry told me that he used to work for the local Coors distributor who also had Guinness in their portfolio. Larry would sell Guinness into his Coors accounts and then switch all of the beers at the account to “Guinness Gas,” a blend of 75% nitrogen/25% carbon dioxide that is also known as beer gas, to make things simpler for the account. Anything to make serving draft beer simpler is the sort of customer service that bar-owners love from their beer distributors and Larry knew how to make his draft accounts happy!
But Larry’s suggestion of simplicity was also his way to gain more business at his accounts because any slow-moving beer dispensed with beer gas will lose its carbonation over time and then customers complain of flat beer. Knowing that this would happen to some beer, Larry could later return and suggest a faster selling brand to take the tortoise’s place. He was one clever rascal.
Your description of what is happening to your keg of Belching Beaver Peanut Butter Stout fits into Larry’s gas trick. Belching Beaver Peanut Butter Stout is available in two versions. One is a normally carbonated beer and the other is nitrogenated. It sounds like you are using mixed gas to push normally carbonated beer through a stout faucet. The beer dictates the correct gas blend, equilibrium pressure, and temperature that fits the gas level set at the brewery. This one simple instruction, set the keg at the equilibrium temperature and pressure for the beer, is total Greek to most people who deal with draft beer. And even when the idea is not obtuse, no keg that I have ever seen comes with carbonation specs or a suggested serving pressure and temperature. This is totally crazy because the brewery sure as heck knows the carbonation or mixed gas level in their beer.
Let’s take a deeper dive into what may be happening in your keg of Belching Beaver Peanut Butter Stout. According to Belching Beaver’s website, this brand is available as a normally carbonated and a nitrogenated beer in bottles. For the sake of thorough discussion that can benefit all readers of BYO, I am going to assume that two versions are also available in kegs. When a carbonated beer is dispensed with carbon dioxide, the gas’ gauge pressure is usually about 12 psig (83 kpa) at 38 °F (3 °C). But when the same beer is dispensed with mixed gas at the same pressure, carbon dioxide in the beer moves into the headspace where the concentration of carbon dioxide is lower. Some nitrogen also moves from the headspace into the beer, but this is normally not obvious when the beer is poured. Over time, the beer in the keg begins to go flat, and the rate of change increases as the volume of beer in the keg decreases. Although this alone does not explain the initial foaming, it does explain the short-lived foam and may explain what is happening to your beer.
Since the earth’s atmosphere is 79% nitrogen and the nitrogen concentration in a bubble of nitro beer foam is typically 75%, there is no gradient “pulling” the gas out of the bubble.
So what happens when a normally carbonated beer, or a carbonated beer that is slowly being flattened with beer gas, is served through a stout faucet? They usually foam like crazy because stout faucets have a flat disc with five small holes (if based on the Guinness tap design) that is designed to cause gas breakout from the beer. Without this special plate, nitrogenated beers don’t do anything special when poured except produce a totally flat, and unexceptional looking pint. The very, very foamy pours you describe fit with how a carbonated beer poured through a stout faucet behaves. The short-lived foam is also consistent with this scenario because once most of the carbon dioxide has been stripped from the beer and the foam settles, there is not much gas left to keep the foam from collapsing.
Nitro beers, the flipside of this discussion, have very stable foam because the gas in the nitro beer bubbles is a mixture of nitrogen and carbon dioxide. Since the earth’s atmosphere is 79% nitrogen and the nitrogen concentration in a bubble of nitro beer foam is typically 75%, there is no gradient “pulling” the gas out of the bubble. This makes nitrogen foams very stable. They do eventually collapse as the liquid in the bubble wall thins due to gravity and surface tension effects, but this takes much, much longer compared to carbon dioxide bubbles.
My point thus far is that it is possible that you have a keg of carbonated beer that you are attempting to serve on nitro. And to directly answer your question about needing to wait some time to allow the beer to condition to the mixed gas atmosphere, the answer is “no.” When a keg of nitro beer is put on tap, all that is needed is about 30 psig (207 kpa) pressure to push the beer from the keg and a stout faucet. Furthermore, if you are starting with a normally carbonated beer, you cannot morph this brew into a nitro beer by simply hooking the keg up to mixed gas, increasing the pressure, and waiting for 1–2 weeks. The reason this method is not effective is because of the carbon dioxide in the beer; nitro beers contain a much lower carbon dioxide content than normal beers. In order to convert carbonated beer into nitro beer, carbon dioxide must be removed and nitrogen must be added. This topic is a deep rabbit hole that I am going to avoid entering. Suffice to say, removing carbon dioxide to the right level is not easy.
Whether you are tapping a keg of nitrogenated beer produced at home or purchased from a commercial brewery, the dispense method is the same. The basic, short-distant, direct draw, set up consists of a source of mixed gas (75% nitrogen/25% carbon dioxide), about 4–6 feet (1.2–1.8 m) of 3⁄16-in. (5 mm) beer line, a keg of beer stored at about 38 °F (3 °C), and a stout faucet. The standard-bearer for nitro beer is Guinness, because Guinness pioneered and perfected the technology. One of the interesting things about how stout faucets work is the need for velocity going into the tap. If nitro beer velocity is slowed by reducing the dispense pressure, gas break-out is reduced and the beer does not foam and cascade properly. For this reason, it is important to dispense nitro beers in the 30–35 psig (207–241 kpa) range. Not only does this pressure maintain the gas equilibrium established at the brewery, it provides the high velocity required by the faucet.
I will finish with a pragmatic suggestion. When all else fails, pick up the phone and call the brewery. I like asking simple questions and would begin with something like, “I just bought a keg of your peanut butter stout and want to make sure that I am using the correct gas pressure and temperature to match the gas specifications for your great beer.” It could be that you have a keg of beer that was not properly nitrogenated at the brewery, and that you are doing nothing wrong on your end. Cheers!
