Scavenging Oxygen, a Propane Heating System, and Water Chemistry

Q If you’re adding priming sugar when bottling, will any oxygen that gets into the bottle be scavenged by the residual yeast during bottle conditioning? Do you have to worry about oxygen causing your brew to become stale?

Michael Roth
Evansville, Indiana

A Oxygen is a problem for beer at all stages of the process following the early stages of fermentation because many of the flavor-active compounds created by yeast are changed, i.e., chemically oxidized, when exposed to oxygen. Unfortunately for us brewers, these oxidation reactions are very fast and many of the products of oxidation are easily detected. It’s also a bit of a bummer that yeast typically do not mop up oxygen faster than it can react with beer flavor compounds.

When I was a young brewing student in the early 1990s, the most common method used to measure air in packaged beer was with a Zahm and Nagel headspace gizmo. These setups have a piercing device that allows for the measurement of pressure and temperature in bottles and cans; pressure and temperature are then looked up in a Zahm and Nagel chart to determine how much carbon dioxide is dissolved in the beer. The Zahm and Nagel device can be equipped with a separate apparatus that allows gas to literally be shaken out of the beer sample where it flows into a special glass burette filled with sodium hydroxide. Carbon dioxide is consumed by the sodium hydroxide but nitrogen and oxygen (not much present in beer because of its reactivity) remain in the burette and are measured as headspace air.

In the early ‘90s, it was not uncommon for packaged beer to contain 0.5 mL, and often more, of headspace air. This equates to about 400 parts per billion (ppb) of dissolved oxygen (DO). Today, brewers become concerned when their package DO is above ~30–50 ppb of DO. Packaging technology has made enormous strides over the last 30 years, as have methods used to measure DO.

I tell this story because homebrewers have become hyper-concerned about oxygen because commercial breweries are hyper-concerned with DO. Our concerns as homebrewers are like those of commercial brewers, except for one main difference; homebrewers don’t have to worry about our beers sitting in some unknown place at some unknown temperature for extended time periods waiting to be picked from the shelf. I think it is very important for homebrewers to keep that fact in mind when worrying (or not worrying) about certain brewing details. 

Empirically, it does seem that bottle-conditioned beers taste oxidized less often than other beers. This observation is well-documented in the homebrewing and commercial literature and is usually attributed to yeast being able to scavenge oxygen. I have never been sold on this explanation because oxidative reactions are faster than oxygen uptake by yeast. Indeed, research over the last 20 years or so provide clearer explanations of these empirical observations. A study by D. Saison, et al., in 2010 titled “Decrease of Aged Beer Aroma by the Reducing Activity of Brewing Yeast” where aged beer containing aged beer aromas was almost entirely stripped of these staling aldehydes during refermentation (Journal of Agricultural and Food Chemistry 2010 58 (5), 3107-3115). A more recent study in 2023 by De Clippeleer, et al., related to non-alcoholic and low-alcohol beer (NABLAB) production, showed that yeast selected for NABLABs biochemically reduce wort aldehydes associated with worty and stale aromas, thereby greatly reducing these off-aromas (“An In-Depth Comparative Study between Commercial Alternative Brewing Yeasts in Low-Alcohol and Alcohol-Free Beer Production,” ASBC Meeting Abstracts, 2023).

I recently tasted three NA (non-alcoholic) experimental beers brewed at the Fermentis Academy in Lille, France. The control beer was fermented with SafBrew LA-01, a maltose-negative yeast (it doesn’t ferment maltose sugar). The first experimental beer was first kettle-soured with Lactobacillus plantarum before wort boiling and fermentation using the maltose-negative strain. The second experimental beer was produced by adding fruit aromas to the kettle-soured NA. The control beer had a perceptible wortiness, however, both beers that were kettle-soured lacked worty aromas associated with wort aldehydes, demonstrating that lactic acid bacteria also reduce aldehydes.

OK, time to wrap these tidbits of information into something useful. For starters, I am not suggesting that dissolved oxygen is not a problem in beer. Focusing on methods to minimize oxygen pick-up after the start of fermentation are, without argument, important to brewing. Many homebrewers these days have taken an anti-rack position because of concerns about oxidation. I use simple methods, including a carboy fermenter and a keg for my secondary. It’s very easy to fill a keg with sanitizer, blow it out using CO2, recover the sanitizer for later use in the soon-to-be cleaned carboy, and rack beer from the carboy into the secondary without worrying about oxygen pick-up. I usually cold crash this beer after whatever time at fermentation temperature is required to finish the beer, store for a few days, and rack into another keg for serving. Up until now, minimizing oxygen pick-up has been relatively easy.

For those of us who bottle, there are a few options for filling. My preferred method is using a counter-pressure filler, even when my plan is to bottle-condition, because these fillers allow for beer containing CO2 to be filled with minimal foaming, intentionally foamed or fobbed after filling to push gas out of the headspace, and then capped with minimal oxygen pick-up. Commercially available bottle-conditioned beers are usually filled with about 2.2 volumes of CO2 so that fobbing before capping is possible. High package airs occur when this step of the filling process is not properly performed. This is where homebrewers tend to deviate from commercial norms.

Most homebrewers use something like a BeerGun® or a flexible hose that can be pinched to stop flow to fill bottles with still beer from a carboy, bottling bucket, or Corny keg. Still beer contains too little CO2 to fob and always leaves headspace gas, which is 20% oxygen, in the top of the bottle. While it’s tempting to leave minimal headspace in the bottle, that trick often results in bottle breakage. We’re now back to the beginning of this story where bottled craft beer in the early 90s often had very high package airs. I drank my fair share of great microbrewed beer back in that time and enjoyed more fresh beer than oxidized beer. The game changed as more beers started to show up on warm shelves, in places further and further from the brewery, and sat for longer and longer time periods. You can control this at home.

The other thing homebrewers without sophisticated bottle fillers can do is dose fresh yeast with priming sugar before packaging. Fresh yeast will not only carbonate your beer faster than whatever happens to be hanging around after fermentation and aging, but it will be in a better metabolic state to reduce staling aldehydes that develop as oxygen reacts with alcohols. Most bottle-conditioned beers contain about 500,000 yeast cells per mL, roughly 10–20 times less than wort pitch rates, and brewers wanting to dose fresh yeast need not go overboard. This last bit is the key that recent research explains; active yeast converts staling aldehydes back to the compounds, primarily alcohols, they were prior to oxidation like an oxidation eraser. Thanks for the great question that led me to some interesting references!

Q I have been brewing for several years and utilizing the BIAB (Brew-in-A-Bag) method. My quest has been looking for a way to use my propane system to hold my mash at the desired temperature during the entire mash. I think a propane controller hooked up to a thermometer that is in the mash or thermowell would work. I have seen “camping” propane water heaters that use batteries with a digital temperature set to maintain a specific water temperature. But two problems are 1) The setup can’t get temperature up to mash temperatures and 2) I don’t want to run mash through the tubes. Do you have any ideas or advice?

Bob Weschler
Bumpass, Virginia

A I think I have a solution to your quest that will work well without costing much money. All you need for this project is your propane burner, a pot, an immersion wort cooler, a temperature controller, such as an Ink Bird or a Baylite unit with a heating output plug, and a submersible water pump rated for high-temperature applications. You may have most of these gizmos laying around already. The pot can be your brew kettle or a smaller pot dedicated to mash heating, the immersion cooler can be used both for mash heating and wort cooling, and the temperature controller can be used for other brewing functions like keezer control. The only item that may fall into what Alton Brown of “Good Eats” calls a mono-tasker is the submersible water pump; the good news is that these little dudes are easy to find out on the interweb for about $50.

The basic setup uses your propane heater to heat a pot filled with water, the submersible pump to deliver hot water to the immersion coil (use high-temperature, braided hoses connected to the coil using hose clamps for safety), and the temperature controller to turn the pump on and off (pump must be plugged to the outlet designated for heating and the heating differential set to about 2 °F/1 °C). A good way to conserve water is to use the same water for mash heating and sparging. The water temperature is not critical if it’s about 10 °F (5 °C) hotter than your mash temperature set-point. You can either set your propane burner on the lowest fire to continuously heat the water or you can fire it on and off as needed.

In practice, consider using something like a metal grate to prevent the submersible from touching the bottom of the kettle and consider heating your water pot and immersion coil before mashing-in so that you don’t cool the mash with a cool coil. After your water and coil are hot, mix mash water and malt in your grain bag, let the mash sit for about 10 minutes to allow some mash thinning from enzyme activity, gently wiggle the immersion coil into the mash so that the coil is immersed, and drop the temperature sensor (make sure it is totally sealed and able to be dropped into liquid) into the mash.

Assume you start your mash at 149 °F (60 °C) and you have your controller set to 149 °F (60 °C) with the heating differential set at 2 °F (1 °C). When the measured mash temperature drops to 147 °F (55 °C), the pump will turn on and pump water through the immersion coil until the measured temperature is 149 °F (60 °C). Two practical problems with this design are short cycling of the pump and temperature stratification within the mash. The best way to address short cycling is to keep the differential setting to about 2 °F (1 °C) or greater. And the simplest way to deal with stratification is to gently stir the mash when the heating pump is turned on.

This basic setup keeps things simple without pumping wort or mash through a heater. It also closely mimics how commercial systems heated with steam operate. Hope this helps you get to where you want to go!

Q I have been an all-grain homebrewer for almost 15 years now. I typically start with reverse osmosis (RO) water and add Ca+2, Mg+2, Na+, HCO3 and Cl as needed, depending on the beer that I am brewing. I measure mash pH and am normally within the recommended range of 5.2 to 5.5. What I would like help with is a formula for calculating/estimating mash pH so that I can make appropriate pre-mash acid/base adjustments vs. trying to catch up after the fact. I have used the Braukaiser spreadsheet but would like to see a summary of the actual formulas and supporting data used/needed to make reasonable pre-mash pH estimates. I am an engineer by training, so I’ll gladly labor through the math. 

Dennis Sopcich
Loves Park, Illinois

A Being able to predict mash pH based on brewing water composition and grist bill is something of great practical use to brewers. Clearly not all beer styles brewed in Munich, for example, are a good fit with the alkaline water in Munich without some adjustments and having some way to guide these tweaks before a brew is the general aim of many water calculations. The fact is that all such calculations are approximate because there are simply too many variables that affect mash pH, including water, malt, mash profile, boiling duration for decoction mashing, and mash thickness. I have spent a fair amount of time digging into your question and can provide some answers, so read on!

The most recent version of Kai Troester’s water calculator I could find on the Braukaiser website is version V1.58 dated September 16, 2012. The bad news is that this spreadsheet is password protected and the formulas are hidden. That’s probably why you submitted this question. The good news is that I am persistent with Excel and was able to find a tool to remove the password! Sorry Kai, but I had to pick your lock.

Let’s start with a summary of how Kai’s water spreadsheet is written. This tool is based on the work of Paul Kolbach that was first published in 1951. The translated title of his work is “The Influence of Brewing Water on the pH of Wort and Beer.” A.J. Delange translated pieces of this work collected by John Palmer and some of the German text was cleaned up by Kai Troester for translation. The translated document is not dated, but can be found at Kolbach developed the brewing concept of residual alkalinity (RA), expressed in terms of equivalents of calcium oxide, and came up with an easy-to-use factor equating +/- 10 units of RA to +/- 0.3 pH units. Let’s assume we produce wort using distilled water for mashing and sparging and our post-boil wort has a pH of 5.6. If we repeat the same brew with water with RA = +10, the predicted post-boil wort pH is 5.9. The same logic can be applied to mash pH estimation.

In Troester’s tool, he begins by calculating RA and applies a correction factor for mash thickness to account for the differences between predicted wort pH and mash pH (see for a review of how to calculate RA). Troester references his excellent white paper titled “The Effect of Brewing Water and Grist Composition on the pH of the Mash” published on his Braukaiser website where he provides extensive data related to the general topic, including specifics about mash thickness, mash pH, and how these relate to Kolbach’s wort pH rule. The takeaway here is that RA = +/- 10 °dH (degrees of German hardness) equates to a +/- 0.2 mash pH change when mash thickness is 4 parts water to 1 part malt (wt/wt). That’s a bit on thin side for most homebrewing (3:1 is more common), but as the data in Table 1 shows, mash thickness only has a minor effect on predicted mash pH.

Troester’s tool also calculates the predicted pH of mash using distilled water where RA = 0. This is where things become a little odd. Because distilled water has no RA, mash thickness does not affect predicted mash pH and the value that is returned is based solely on color and a big assumption about all pale malts. When color is set to 2 SRM, the predicted pH of mash produced from distilled water is 5.57. Not only does the pH of mashes made from different pale malts vary quite a bit, but it’s usually higher than 5.57. Most North American pale malts these days have a reported pH based on ASBC (American Society of Brewing Chemists) congress mashing of around 5.9. The easy way to use this information is to increase his estimates based on known values obtained from current malt analyses. You can see from the data in Table 1 that the predicted pH changes based on wort color and mash thickness are linear over the range shown, so the adjustment can also be linear.

Troester’s 2009 white paper takes a deep and very interesting dive into the topic of color, but incorporating the results of his mash trials into a single calculation is not simple because pale malts, crystal malts, high-kilned, and roasted malts all affect mash pH differently. In his Braukaiser calculator, he uses a single term combining beer color, % roasted malt, and % non-roasted malt as the way to bring specialty malts into his prediction of mash pH. Note that on a beer color basis, non-roasted malts, assumed to be crystal malts used in his pH shift calculation, are more acidic than roasted malt. This term is calculated by the following:

pH Shift from Color = (-) {(Beer Color in SRM) x [(0.21 x % non-roasted malt) + (0.06 x % roasted malt)]}/12 °Plato.

Although the Braukaiser pH shift from color term appears to be based on solid data, it seems to overestimate the effect of malt color on mash pH. Table 2 shows predicted mash pH at a single mash thickness using alkaline water (RA = 10 °dH) over a range of colors and their corresponding roasted malt component. Troester’s plots of mash pH versus beer color in his white paper don’t fall below about 5.1 when color is derived from roasted malt, yet the predicted mash pH from the combination of 10% roasted malt and 90 SRM is 4.35.

What does this all mean? In my opinion as someone who has written lots of spreadsheets, any review of a spreadsheet is likely to find some oddities. I noted a few because you asked how this tool is written. It’s also my opinion that Kai Troester developed a user-friendly, predictive tool to help navigate the deep topic of water chemistry. If I were to edit this tool, I would “unbury” the pH from base malt and make that an editable variable. I would also spend more time looking at the pH shift from color because it doesn’t pass the sniff test; other references coupled with my own brewing experience are not aligned with that metric.

It’s weird; every time I remove a liter from the brewing water well, it has more water when I return! This review is a good reminder that these types of tools are predictive and are never perfect. Users must be prepared to take notes and adjust their subsequent brews based on the results of the present. That’s my view on the meaning of this exploration.

And back to you, Dennis. Engineers like to understand their tools. Your question sent me on a fun quest that included watching numerous YouTube videos on how to unprotect Excel sheets when you don’t have the password, reading multiple articles about water, and digging into a complex spreadsheet. If you want to learn more, start with figuring out how to sneak past the lock!

Issue: March-April 2024