The Reality of Oxygen Ingress Part 1: The Hot Side


We talk quite extensively, almost as an afterthought, about oxygen ingress and why we want to eliminate it, but what are the actual values? What can you expect in terms of numbers? Let’s take a quick look at some of the known quantities and review some scenarios. Many have asked about the maximum DO levels specified in our original GBF (April 2016) “Helles” paper and struggled with understanding how they are achievable. Let’s discuss the why and how of eliminating oxygen.

Here is a high level visual representation of the process (see Notes on Dissolved Oxygen here for the basis):

From the chart above we can view 2 distinct phases: Wort Production (hot side) and Beer Production (cold side) with Spunding and Packaging representing a special subset of Beer Production and the cold side process as a whole.

So ultimately, if you are to have a conversation about the avoidance of oxygen in your brewhouse, you have to ask your self the fundamental question: WHY? Why do I want to go through the effort? The answer is deceptively simple: Malts contain certain volatile phenolic compounds that when oxidized are removed as a flavor compound in the wort. Your mash smells in the brewhouse are an example of this compound being oxidized. One of the fundamental tenants of brewing using Low Oxygen methods is the desire to save these “sacrificial lambs” and preserve the fresh grain flavors of the wort through the hot side, cold side and packaging phases.

With that said, there exists another pressing question that invariably pops in in a conversation about the topic: Why do I have to de-oxygenate my water? Tap water, as well as RO water and Distilled water, can be verified to have as much as 8-12 ppm of dissolved oxygen. With a target of < 1 ppm dissolved oxygen throughout the entire hot side of the brewing process, you can quickly see that untreated source water makes it completely impossible to get the characteristic “fresh grain” flavors in wort that are the hallmark of the Low Oxygen methods. So if you resign yourself to some method of de-oxygenation of your source water, you can be sure that dissolved oxygen levels can be reduced into the 0.15-0.5 ppm range. Great right? Then why do you have to add antioxidant compounds to this water?

The process of mashing in, when not altered to eliminate splashing and unnecessary aeration, can add up to 1-3 ppm of dissolved oxygen. Yikes! The fact that oxygen solubility increases at mash temps on the order of 4-5 ppm, you can quickly see that if the water you mash in with is only de-oxygenated, and not treated with an additional antioxidant, that you will blow by the target of < 1 ppm dissolved oxygen for the hot side of the process. Metabisulfites have a scavenging power of 5:1, meaning that for every 5 ppm of metabisulfite you use to treat your water, it can scavenge 1 ppm of oxygen. So why can’t you just add a bunch of metabisulfites to your strike water in lieu of de-oxygenating it? Let’s run the numbers:

DO for Mash in = 1-3 ppm

DO for Source Water = 8-12 ppm

Total DO = 9-15 ppm

NaMeta Dosage = 100 ppm

Portion of Dosage required to combat DO at Start: 45-75 ppm

You can clearly see that 45-75% of your dosage of antioxidants will be burned up before you even start mashing! This assumes 100 ppm of metabisulfite as well, which is the upper limit. That leaves you with very little margin to play with across the rest of the process. Add to that the atmospheric diffusion of oxygen into your wort, which is on the order of 1-2 ppm/hour, as well as the desire to reduce metabisulfite dosage rate, and you can quickly see your margin for error disappear before your eyes. This excludes the possible points of ingress in equipment, which add an additional layer of complexity, especially when you are just starting out. Sounds like doom and gloom, right? Can you see why people were so worried initially?

Fret not! There are extremely simple things you can do from a process and equipment standpoint that will help eliminate these points of ingress, put physics on your side and allow you to reduce your antioxidant dose to much lower than the upper limit of 100 ppm. Let’s consider the “Big Three”:

  • Mash Capping – Capping you mash limits the liquid to atmosphere interface, reducing the contact with air to the wort and invoking the square-cube law. This can be as simple (heavy duty foil) or as complex (SS lids with LocLine recirculation outlets) as you’d like.
  • Underletting: By filling the MLT from below, you instantly minimize splashing and unnecessary aeration during the mashing-in process.
  • Gentle Stirring: By gently stirring the mash only enough to ensure good mixture of grain and water, you further minimize aeration.

With just these simple process and equipment changes, coupled with de-oxygenation and treatment of strike water, you can instantly reduce your metabisulfite dosage in half, if not more. Further points of interest for process changes and equipment troubleshooting are as follows:

  • Lauter Capping: Capping the BK as you lauter is another very easy, low tech way of limiting atmospheric ingress to your wort.
  • Tightening Fittings and Hoses: Tightening fittings to pumps and other equipment can reduce even further the potential for oxygen ingress on the hot side.

As you can see, the handful of process and equipment changes above don’t require a ton of investment or energy. They are simple things things that can be integrated immediately into your brewing routine. De-oxygenating can be in the form of a Pre-boil, or if you find that method to time and labor intensive, the yeast scavenging method (Thanks Bilsch!).

In Part II, we’ll talk wort cooling, trub separation and aeration, as well as how they affect dissolved oxygen content in your Low Oxygen wort.

Liked it? Take a second to support Big Monk on Patreon!