Methods of the Low Oxygen Brewhouse
What is low oxygen brewing? Let’s make a fundamental assumption about the malt we use in brewing: There are malt-derived phenolic compounds that exist and gives un-oxidized wort a distinctive fresh flavor. Controlling dissolved oxygen (DO) levels preserves these fresh malt flavors in the grains by protecting them against oxidation. The key word here is protection as opposed to creation. This is a passive process. You are not creating anything that isn’t in the grains themselves.
There may not be copious amounts of reference material that speaks to this phenolic compound directly, but we know from tasting examples of our favorite continental lagers from places such as Ayinger, Weihenstephaner, Augustiner, Andechs, and the like that this distinctive flavor plays an important role in the overall perception of the beers. If you were to focus your attention on a single, unifying flavor component as representative of the phenolic compound we assume, it would be the fresh, lingering, and crisp malt flavor prominent in all the best examples, as well as the examples produced from utilizing low oxygen methods. It can also be seen through the design of modern brewhouses that address oxygen pick-up from all stages of the process. George Fix, in his great Principles of Brewing Science, touches on the potential presence of a low weight phenolic compound that seems most likely to be our smoking gun. German Brewing Forum member “Techbrau,” a scientist and brewer, sums up the concept logically and succinctly in a past post from the American Homebrewer’s Association forum:
“Oxygen has more than one pathway to react with things in the mash. The Fenton reaction is only one of these pathways. Another set of major oxidative pathways are through naturally occurring enzymes found in the malt, such as lipoxygenase and polyphenol oxidase. Polyphenol oxidase is [likely] the real bogeyman here, because we hypothesize that the simple, low molecular weight malt phenols are the main source of the fresh malt flavor [we desire and taste], and polyphenol oxidase is specifically made for catalyzing the oxidation of those phenols.”
So if we assume that these compounds exist and are what we are after, then their preservation becomes paramount. Once these compounds have oxidized, they are gone for good. So with that in mind, let’s discuss the process changes, the mechanical and chemical exclusion principles, and the overall concepts of low oxygen brewing. Bear with us as we try, to the best of our ability, to present a cohesive and informed picture of the whole deal, from point A to point B.
The Differences (Hot Side Process)
Many people are naturally curious as to what some of the key differences are between low oxygen brewing and the more traditional brewing process. Quite a bit of the nuts and bolts process points are the same but there are some distinct areas where they depart from one another. Let’s investigate those differences in order to shed some light on how people can incorporate these methods into what they are already doing.
The biggest departure that low oxygen brewing makes from the traditional infusion mashing process used by most homebrewers is the treatment of the strike water. Most discerning brewers, even those skeptical about the effects of hot-side aeration/oxidation (HSA/HSO) already take steps we advocate from mash-in, such as underletting, reducing splashing/aeration of mash, using fresh, high-quality grain, etc., with just a few exceptions. Where the two methods differ most dramatically is that low oxygen brewing demands that the strike water be pre-treated (both mechanically and chemically) to remove all DO. This is accomplished by pre-boiling the water or using a method of yeast de-oxygenation coupled with adding targeted amounts of sodium or potassium metabisulfite as an active oxygen scavenger. The end result is strike water with ~0 ppm of DO content.
Why is this important? Strike water, in most cases, is already saturated with oxygen during mash-in (oxygen solubility at common strike temperatures can range from about 4–5 ppm). The goal of implementing these methods is to limit oxygen intrusion to less than 1 ppm on the hot-side and mashing into saturated strike water means that you are above that before you even get started!
Here are steps that everyone can take to limit oxygen intrusion on the hot side of the process, with some information on why it is so important:
1. Pre-treat your strike water
Boiling your strike water drives off nearly all the DO in it. This is due to the oxygen solubility at 212 °F (100 °C) being ~0 ppm. By maintaining boiling temperature for about 5 minutes, you guarantee that the entire volume has been subjected to 212 °F for a long enough duration. You then force chill the water to your desired strike temperature and treat it with an appropriate amount of metabisulfite (see Table 1 below). Alternatively, the yeast de-oxygenation method can be employed in lieu of pre-boiling. See Procedure 1 at end of article for detailed steps on both methods. Using metabisulfite has effects on brewing water formulation. Consult Table 2 for sulfate, sodium, potassium, and pH elements to be tracked.
2. Grain milling/crushing
You want to minimize the time between when the grain is milled/crushed and mash-in due to the fact that activation of oxidative malt compounds such as lipoxygenase (which resides in the acrospires of the malt kernel), as well as exposure to atmospheric oxygen, can set in. This is where owning your own mill is a plus, but in the grand scheme of things, this is a lesser concern. If you can get your grain crushed on brew day then that is ideal. Try to limit the time between grain preparation and mashing.
3. Mash-in gently and underlet strike water
It is important to take care when mashing-in. Underletting is the preferred method of introducing strike water. This can be accomplished by adding grains to the mash tun and then gravity draining or pumping strike water through the mash tun outlet valve, or simply adding the grains to the mash tun and running a line to the bottom of the mash tun and using gravity to drain the strike volume in. Gentle but thorough mixing is required. Take care not to splash or otherwise unnecessarily aerate the wort when stirring or transferring. Mashing-in can add up to 2 ppm of DO so it is important that you be gentle here. Also, ensure all physical connections for fittings are tight and leak free.
4. Utilize a “mash cap”
We advocate adding a “mash cap,” typically a stainless steel pot lid or cake pan that floats on top of the mash or a fixed unit held in place at the top of the mash with a gasket, which significantly reduces the exposed surface area of the mash (you can see this in the picture on at the top of this story). Since atmospheric diffusion is directly related to the amount of surface area of the brewing vessel, and most homebrewing vessels have a large surface area-to-volume ratio, adding a physical barrier at the surface greatly reduces the atmospheric diffusion of oxygen. This is important, especially considering the time we spend mashing. Atmospheric diffusion of oxygen at the air to liquid boundary can reach a rate of 1 ppm/hour.
5. Utilize the “no-sparge” method
We advocate the use of “no-sparge,” full-volume mashing. The purpose is two-fold:
a.) It cuts down on the potential for oxygen intrusion from sparging.
b.) It eliminates the need to pre-treat the sparge water.
We understand that because of vessel sizing, some may not have the capacity to mash at full volume. In this case, it’s important to treat the sparge water you use the same as the strike water, i.e. pre-boiling and treating with metabisulfite.
6. Use Brewtan B or a similar gallotannin
There are a few reasons to incorporate Brewtan B (BTB)/gallotannins (GT) into your brewing. Firstly, many people are using copper chillers, and while we advocate the use of stainless steel if you can, utilizing Brewtan B with a copper chiller is useful in that copper, along with iron and brass, can participate in an oxidative pathway known as the Fenton reaction. BTB/GT act to chelate these trace metals from copper chillers and brass fittings (as well as iron in source water) as well as bind and coagulate proteins and lipids from the mashing process that have the potential to contribute to oxidative reactions later in the brewing process. The standard dosing rate ranges from 0.15-0.26 g/gal (0.04–0.068 g/L) of BTB/GT, which can be added to the mash and boil for those using a copper chiller while stainless chiller users will want to skip the boil addition. The range encompasses both the Wyeast recommended values of 6.83 g/hL for the mash and 4.27 g/hL for the boil, as well as the recommendations of Ajinomoto (makers of Brewtan B) representatives of 4 g/hL for both the mash and boil.
There are also some concerns not directly related to oxygen intrusion on the hot side, such as boiling, that should be addressed. It is important to control heat stress, which can serve to accelerate oxidation and affect the final flavor of the beer. Wolfgang Kunze, author of Technology Brewing and Malting, notes that reducing the level of heat stress during beer production has a positive effect on the flavor stability of the beer produced. For the average homebrewer, there are some simple process changes that can effectively reduce thermal stress in your wort. Limiting boil time to 60 minutes is important. Longer durations introduce the potential for heat stress and an increase in Maillard reaction products. Partially covering the boil kettle and reducing the boil to a “simmer” (as shown in the picture on page 79) will help you target between 6–10% evaporation. This will allow you to use much less heat in order to achieve your boil. Be sure to track your new boil-off and revise equipment profiles in software for future sessions. The subject of Dimethyl Sulfide (DMS) comes up often in discussions about covering the boil and reducing boil vigor. We have found that even a simmer is sufficient enough to eliminate DMS. If you do find that trace amounts of it are detectable, you can either extend the boil 5–10 minutes, or increase your evaporation percentage closer to 10% to compensate.
Ultimately the hot side of the process is where we preserve the flavors we are after. As you can see, nearly all of the process changes from traditional methods are within reach for the average homebrewer. Let’s move on and talk about the cold side of the process.
The Differences (Cold Side Process)
The cold side process is actually an area where we see the most agreement between low oxygen methods and traditional homebrewing processes. We know that flavor stability is impacted enormously by the introduction of oxygen post-fermentation. In fact, most people are already very conscious and more than willing to go the extra mile to limit oxygen contact during this stage.
So then, what are the differences between what we advocate and what most people are already doing? Well, there are some significant ones but nothing that can’t be overcome with some new gear or process changes.
Think of the hot side of the process as filling a balloon with flavor. The cold side represents poking a hole in that balloon. How successful you are at preserving the flavor depends on how small you make the hole. This goes for low oxygen brewing or traditional homebrewing processes. The cold side is your best friend and your worst enemy. The goal of implementing these methods is to limit oxygen intrusion to less than 0.15 ppm (150 ppb) on the cold-side for the best possible results.
It can be done. Here are some steps to take to achieve that and why they are important:
1. Chill as rapidly as possible
You’ll want to chill your wort after the boil is complete as rapidly as your system will allow. Remember that the more time you spend chilling, the more time your hot wort is exposed to atmospheric oxygen. In the grand scheme of things, this is a lower priority, but if you are taking more than 15 minutes to chill your wort to yeast-pitching temperature with your standard immersion chiller, we would suggest either a larger immersion chiller, using a secondary loop with chilled water as a pre-chiller, or investing in a counterflow chiller to speed up wort chilling times. As an added benefit, chill speed also promotes good cold break.
2. Aerate/oxygenate after pitching active yeast
One of the questions we get regularly goes something like this: “If I just spent the time and energy to exclude oxygen, then what’s the deal with aerating/oxygenating after I pitch my yeast? Doesn’t blasting the wort with sterile air or pure oxygen then just negate all that effort?”
In short, the answer is no. We advocate no aeration/oxygenation until after you have pitched active yeast. Remember that active yeast is one of the most incredible oxygen scavengers at your disposal and pitching them hungry and active means they will start consuming oxygen almost immediately. Also, the reaction rate between the wort and oxygen at pitching temperatures is much slower than at mash temperatures. Active yeast combined with slower reaction rates means that the 8–12 ppm you’ll treat the wort to after pitching gets scavenged by the yeast in very short order. There simply is not a sufficient amount of time for it to be damaging.
3. Use closed transfers when moving beer from vessel to vessel
You need to ensure your method of transferring beer from vessel to vessel is closed and that receiving vessels have been purged of oxygen. See Procedure 2 (at end of article) for methods of properly purging receiving vessels.
4. Use spunding to provide natural carbonation
We advocate the use of spunding, i.e. transferring your beer to a vessel with remaining extract and using a pressure relief valve set to a target pressure value in order to use naturally produced CO2 to carbonate your beer. This can be done with a keg and a spunding valve.
Why is transferring with remaining extract so important? Remember that active yeast is nature’s great oxygen scavenger. Transferring with active yeast means that any DO intrusion incurred during transfer is scavenged by the yeast and the finished beer will be oxygen-free in the serving vessel.
Why is using natural carbonation so important? For kegging, it is important because even the purest bottled CO2 contains enough oxygen to cause a loss of freshness in your carefully prepared beer. You will still use it to serve your beer, but force carbonating is out.
Recipe Formulation
Low oxygen brewing gives the brewer a fresh perspective to work with when creating new recipes or revisiting old ones. Rather than present a fully formed recipe, there are some high level considerations for recipe formulation that should be discussed. Color reduction can be ≥ 20%, meaning that the actual wort color can be ≤ 80% of color predicted by the Morey equation. This is an empirical observation and will vary depending on system and process.
Smaller percentages of caramel and roasted malts may be in order when you start out. More is not more where malt is concerned and discretion will prevent a muddy beer. Sinamar® is a very useful tool in matching color of commercial clones or darkening without adding flavor. It may be necessary to revisit old recipes and reconsider their construction. Consider conducting a mini-mash when entertaining new malts or attempting to taste flavors before use.
Wort flavor can take on characteristics of certain food products: Cereals, breads, honey, fresh dough, hard pretzel, dark chocolate, and hard candy. These are the true flavors of un-oxidized malt and you can use them as a benchmark when comparing pre-boil wort flavor to knockout wort flavor. If you notice a stark difference between these two you may have to adjust your process to prevent DO intrusion or take greater care to reduce heat stress in the boil.
With regards to bitterness, hop schedules, and IBU calculations, hop flavor will possess more “presence” and “brightness” for lack of a better word. Hop aroma will be enhanced.
Conclusion
In the evolution of any hobby you find that the path to your ultimate goals is asymptotic. Much of your skill-building and improvement exists in the large portion of the curve before it swings upward toward infinity. Brewing, however, has a flavor component. What we have tried to bring to the forefront with this topic is less a statement of divisiveness in a niche community and more of a desire to help people looking to make the best beer possible. In fact, that can be said to be the motto with no exceptions: Make the best beer you can possibly make. It has been the goal from the first time you put malt extract into a stockpot and it carried through to the first time you cracked open barley kernels and soaked them in hot water.
We believe that every brewer can improve every beer with these methods in some way or another. We wanted to give brewers a synopsis of these methods that untangles some of the information that exists on the subject. We hope brewers of all skill levels use this article as a stepping stone towards re-invigorating their interest in brewing, improving their methods, and saying to hell with the curve as they continue toward brewing perfection.
Procedure 1:
Methods of Pre-Treating Strike Water For Pre-Boil:
1. Bring strike water to a vigorous boil for 5 minutes.
2. Chill the strike water as rapidly as possible to the desired strike temperature.
3. Dose strike water with metabisulfite when temperature reaches 200 °F (93 °C), then continue chilling.
4. Use the correct dosing for strike (or sparge) water (Table 1).
5. Add grain and brewing salts.
6. Underlet the treated strike water to the grains, if possible.
7. If adding water from above, or lowering in a grain bag (single vessel), do it carefully so as to not aerate the water or splash.
8. Stir thoroughly but carefully if using single infusion to ensure proper mixing. Use recirculation (with return below liquid line) if direct-fire step mashing.
For Yeast De-Oxygenation*:
1. Prepare a solution of dextrose and neutral dry yeast at a rate of twice your strike volume in grams (i.e. for 5 gallons use 5 x 2 = 10 grams each of bread yeast and dextrose.)
2. Ideal timing for dough-in following this treatment of strike water is between 1–2 hours.
3. Follow steps 3–8 in the above pre-boil steps.
*Credit for the creation of this method goes to Russ Nickel (aka Bilsch), a close friend of lowoxygenbrewing.com and our administrative team.
Procedure 2:
Methods of Properly Purging and Transferring in Receiving Vessels For Purging with Sanitizer:
1. Clean receiving vessel. Fill it to the brim (may have to shorten gas dip tube) with a non-foaming sanitizer such as Saniclean or Iodophor.
2. Push the entire volume of sanitizer out of the keg with CO2.
3. Perform a closed transfer from fermenter to the receiving vessel:
a. For a keg-to-keg transfer you’ll need to jumper the gas posts and liquid posts.
b. For traditional fermenter-to-keg transfers you’ll jumper blowoff to gas-in and output valve to liquid-out.
4. Close receiving vessel and attach spunding valve.
5. Set pressure on valve as desired (based on temperature and residual carbonation).
6. Allow beer to finish fermentation. Check gravity at various intervals to track progress.
For Purging with Fermentation CO2:
1. Clean and sanitize receiving vessel. Empty all sanitizer out of the vessel.
2. Make the proper connections depending on fermenter type:
a. For keg-to-keg connections you’ll need to jumper the gas-out post on the fermenter to the liquid-out on the receiving vessel and connect the gas-in post of the receiving vessel to a blow-off container.
b. For traditional fermenter-to-keg connections you’ll need to connect the fermenter valve to the liquid post and the keg gas post to a blow-off container.
3. Follow steps 3–6 in the above purging with sanitizer steps.
Get more information from the authors on low oxygen brewing at www.lowoxygenbrewing.com
