Examining Oxygen Ingress: Should I Pre-boil?

Oxygen

INTRODUCTION


One of the cornerstones of Low Oxygen brewing (and probably the most contentious step) is the pre-boiling of strike water. The reason it is so important is that it knocks down the dissolved oxygen in the water to zero, and furthermore, it  gives the brewer a “clean slate”. Yet many people have balked at this step in particular siting issues with heat times adding to an already tight brewday. People early on also questioned why, if they were going to dose the water with active scavengers anyway, did they have to pre-boil? Let’s examine and revisit the idea to learn why it is so important and how the brewer can adjust their process in light of not doing it.

It is obvious that if the goal is to eliminate dissolved oxygen in strike water, the pre-boil is hands down the most surefire way to do that and not impact anything else downstream. It is simply heating the water to boil for 5 minutes. The problem that arises is accounting for the time it takes to get even a small volume of water to boil. For instance, my 1.25 gallon batches often only require 2.5-2.75 gallons of strike water, yet my 1.3 kW burner takes almost 45-60 minutes to get there. Even my stovetop takes 30-40 minutes to boil even that small a volume. So is there wiggle room here? Let’s take a deeper look.

THE GENERAL IDEA


Oxygen ingress into water is function of pressure and temperature. For the purposes of this discussion, we are assuming atmospheric pressure over a range of temperatures. A nice visual can be found here. I extrapolated these numbers into excel over a temperature range of 140-212 F:

I next tried to use these values and see how they matched up with empirical data from my good friend at The Beerery. From the chart above and the extrapolated values in Excel, it can be shown that many of the numbers originally quoted in the original 2016 GBF “Helles” paper hold true, and therefore, it is safe to assume the following:

1.) Oxygen solubility at mash temperatures is on the order of 4-5 ppm.

2.) Dough-In will net you ~ 2 ppm.

3.) Atmospheric diffusion will net you between 1-1.3 ppm depending on total time spent mashing.

AN EXAMPLE


So let’s run through a simple example:

I have had some times where I am spending almost an hour pre-boiling my strike water. I notice that I get to mash temps pretty quickly and that 185 F takes around 25 minutes. Using the chart in Excel, I see that my DO pickup at 185 F will be ~ 2.34 ppm. I assume ~ 2 ppm for dough-in and since I have a total of 80 minutes active mashing time (dough-in, rest times and ramp times) I will assume ~ 1.3 ppm due to atmospheric diffusion. In this case, since i don’t have the insurance that the pre-boil provides me, I assume a 5 ppm margin and add that to my desired sulfite dose:

2.34 + 2 + 1.2 = 5.64 total DO from process added.

Since I know that the various forms of sulfites scavenge oxygen at a rate of 5:1, I know i’ll need:

5.64 * 5 = 28.2 ppm of sulfites to scavenge the added DO from process. I add an additional 5 ppm of sulfites (protection against the max hot side DO of 1 ppm) as a measure of margin for a total of 33.2 ppm of sulfites.

A YEAST DRIVEN ALTERNATIVE


We would be remiss if we didn’t mention our friend Bilsch’s “Yeast De-oxygenation Method” when discussing alternatives to pre-boiling. As always we appreciate his innovative idea and many people have reported good results using it. Thanks Bilsch!

To help people get an idea of if ,and where, they may want to implement this, I put a simple spreadsheet together:

DO and Mashing

Hope this helps! Cheers!

NOTE: We assume that you are using a mash cap.

DISCLAIMER: We are not advocating the omission of the pre-boil. It is far and away one of the simplest measures to implement and it ensures that you start with 0 ppm DO. With that said, if you are going to take a shortcut, it is our opinion you do it as an informed individual and know what limitations that shortcut may impose on your process. That is the goal of this writeup. One of the things to consider is that if you are using sulfites to counteract oxygen already in the water/wort (an artifact of not starting at 0 ppm), you will have a higher starting sulfite load , and as a result a larger Sulfate, Potassium or Sodium load.