Brewing with Reverse Osmosis Water

You can’t trust water: Even a straight stick turns crooked in it.” – W.C. Fields.

Over the years, I’ve probably had more discussions, debates, and arguments with other brewers over water than just about any other topic. And I think I know why. It’s a fairly advanced topic that requires some scientific understanding, but also significant brewing experience to apply. So those of us who write about beer invariably try to create simple models and descriptions to make the subject understandable to a wider audience. And in doing so, we create advice that people misinterpret as rules, and misapply in situations that were never envisioned.

In the more than 25 years I’ve been brewing, my goals have been to understand what’s going on in my process, to apply controls in places that matter, and to enjoy making great beer. My switch to using reverse osmosis (RO) water has probably been the single largest change I’ve made that allowed me to achieve these goals and to greatly simplify my brewing process while still crafting medal-winning beers.

What is RO Water?

RO water is basically filtered water with greatly reduced mineral content. It’s produced using the reverse osmosis process that uses high pressure and a semi-permeable membrane to remove minerals. The membrane is like a filter that will only allow molecules of a certain size or smaller to pass through. Under normal osmosis, liquid would flow across the membrane in the direction of lowest salt concentration to highest. But in reverse osmosis, the high pressure causes the liquid to flow in the opposite direction, forcing water from the mineral-rich side of the membrane (the water being treated) through the membrane while the concentrated feed water is rejected, thus producing low-mineral water (see the illustration below).

RO water is not the same as deionized (DI) water or distilled water. Those use different processes, although they will also produce water with reduced mineral content. RO water is not mineral-free, but can have 95–99% less minerals than the source water. The source water is often pre-treated to help with the mineral removal. In the RO machine I use, there is a five-stage process: Active carbon filtering, micron filtering, reverse osmosis, post carbon filtering, and ultraviolet (UV) irradiation. These other steps help remove chlorine, metals, organic matter, viruses, bacteria, and other undesirable content. While these steps aren’t part of the RO process, getting water in this condition simplifies my brewing, and is what I mean when I talk about using RO water.

If you think all of this processing is expensive, it’s not. I can buy 5 gallons (19 L) of RO water at my local supermarket for about $1.95.

Advantages of RO Water

RO water is a blank slate; it has very few minerals, so you can use it as a starting point for building brewing water for your purposes. It has very little alkalinity (dissolved carbonates and bicarbonates), so it doesn’t buffer acids much — this means acid additions can easily change pH rather than having to first neutralize these buffers. And (assuming the RO machine is working properly), it is extremely consistent from batch-to-batch. This means you don’t have to worry about variability in your water source, or get water reports to analyze.

If the RO water is processed as I described, it also has any chlorine removed and has other objectionable substances removed. Your water should be good to go for brewing without pre-boiling, filtering, or any other modifications. I normally just do a quick check of total dissolved solids (TDS), which is built into my pH meter. If it’s low, I know the RO machine is working and the water will respond as with previous batches.

I’ve mentioned pH twice but haven’t defined it. Loosely, it’s an expression of how acidic or basic a solution is, with 7 being neutral, lower numbers being acidic, and higher numbers basic. Higher concentrations of hydrogen ions (H+) make a solution more acidic. The scale is logarithmic, so moving one number means the solution is ten times more acidic or basic. pH is an open-ended scale, although most measurements fall within the 0 to 14 range. Most beer-related measurements are even more constrained — for example, most finished beer is in the range pH 4.1–4.5. 

That is a primer on pH, but if you want to dive deeper into the subject check out this story from the BYO archives: https://byo.com/article/the-role-of-ph-homebrew-science/

How Water Impacts the Brewing Process

I see the three main worries about water during the brewing process as:

1.  Does the water taste good? 

2. Can I achieve a proper mash pH for enzymatic activity? 

3. Does the beer taste right for its style?

To achieve the first goal (good tasting water), breweries often pre-treat their water by carbon filtration or pre-boiling. Municipal water suppliers can do some of this work for you, but breweries with their own wells or private supplies must treat their own water. Buying RO water allows you to skip all these steps. Your water is ready to use.

To meet the second goal (a proper mash pH for enzymatic activity), you typically have to lower the pH of the mash to a desired range. References vary on this goal, but I usually shoot for a pH of 5.2 ± 0.1 (Kunze in Technology Brewing and Malting says 5.1 to 5.2 is the goal; he stresses a lower mash pH helps avoid enzymatic oxidation of the mash, which causes premature staling of the beer).

When taking pH readings, understand that pH is expressed as 77 °F (25 °C) by convention, regardless of the temperature of the reaction. pH does vary by temperature (pH can be about 0.3 lower at mash temperature than at reference temperature), but the pH is normally written at the standard reference temperature unless otherwise stated. 

Breweries typically adjust their brewing water to remove or offset alkalinity (carbonates) through boiling, acid additions (mineral acids, biological acids, or acid malt), or lime (calcium hydroxide). Then harden the water through additions of calcium salts (calcium chloride and/or calcium sulfate). Finally, the calcium in the water reacts with phosphates in the malt to reduce the pH. If all of this was calculated properly, the target mash pH is achieved.

With RO water, some of these steps are simplified. Removing alkalinity should already have been done. Salts can be added to reach a target calcium level (which we will discuss later), and the mash reactions are still the same. Some additional pH adjustments may be required with acids or malts.

The final goal (a beer that tastes right for its style) involves making any small adjustments to the flavor profile of the water to better support the style of beer being brewed. This is what I call adjustment of stylistic ions or chemically-inactive ions in the water. These salt additions don’t affect the mash chemistry but can affect the taste of the beer. Adjusting these salts is the same regardless of the use of RO water or water from another source.

Effects of Water Ions on Brewing

Water is often called the universal solvent due to its ability to dissolve so many things, including salts. Salts are solid compounds formed of positive- and negative-charged components. Water readily disassociates salts (causes them to break into separate charged particles or ions), although some salts are more soluble than others.

The various ions from disassociated salts have pH and flavor effects in beer. Let’s run through them:

Calcium (Ca⁺²) — Is perhaps the most important ion for brewing. It’s an important cofactor for mash enzyme activity, helps in protein coagulation (hot and cold break, for those brewers who still remember that clarity is important), and helps lower mash pH by interacting with phosphates in the malt. Excessive amounts can taste metallic and have detrimental effects on yeast performance.

Magnesium (Mg⁺²) — Has some of the same effects as calcium, but less so. It can also lower mash pH but has a disagreeable bitterness and sourness in higher concentrations; it also has laxative effects. 

Sodium (Na⁺²) — Has no effect on the brewing process but has some flavor effects, such as palate fullness. It can taste salty in high concentrations and has been linked to causing high blood pressure.

Chloride (Cl^–) — Adds to the fullness and roundness of beer on the palate. It can contribute to salty flavors when combined with sodium. It is an important flavor ion.

Sulfate (SO₄^-2) — Adds to the dryness of the beer on the palate and can accentuate the sharpness of bitterness. It can be harsh and sulfury in larger concentrations. It is an important flavor ion.

Carbonate (CO₃^-2) — Increases mash pH and provides the alkalinity in water. At mashing pH it mostly exists as bicarbonate (HCO₃^–). It causes problems in brewing by raising pH, and has a chalky flavor. Reducing alkalinity is a major goal of brewers when dealing with water. Carbonate can balance acidic raw materials like roasted malts, however I don’t use carbonate as I add any dark grain additions after the mash (more on this later).

Other ions present in brewing in smaller concentrations include trace elements important for yeast nutrition, such as zinc (Zn⁺²), copper (Cu⁺¹), and manganese (Mn⁺²). Metals such as iron (Fe⁺²) and nickel (Ni⁺⁴) are undesirable and can cause metallic flavors.

I resist making specific recommendations for concentrations of ions in brewing since sources vary so much. For example, Palmer and Kaminsky in Water: A Comprehensive Guide for Brewers recommend 50–150 ppm (parts per million, same as mg/L) of calcium; Fix in Principles of Brewing Science recommends 50–100 (although his cited source recommends 40–100), Briggs in Brewing: Science and Practice recommends 20–150, and Noonan in New Brewing Lager Beer suggests 5–200. Yet the water in Pilsen has less than 10 ppm of calcium, and I don’t think Pilsner Urquell is a problematic beer . . . so hard and fast guidelines don’t always work in real life, or there is more to the story than you think.

For people who dogmatically apply water profiles, I ask the simple question: Who says all of these minerals must come from water? Did malt suddenly become mineral-free when I wasn’t looking? The mineral content of beer does not exclusively come from water, so we should stop pretending that the other ingredients have zero mineral content.

Recipe and Process Considerations

When you use RO water, you aren’t trying to turn literally any kind of water into literally any style. You don’t have a huge range of alternatives to deal with — your options are limited. Some of my methods allow the brewer to limit them even further, which makes brewing very repeatable, consistent, and easy.

Sometimes there are multiple solutions to a brewing problem. When lowering the pH of the mash, you can let the calcium and magnesium (hardness) interact with the malt, you can add liquid acids, or you can add acid malt to the grist. The hardness interaction will always happen, but is often insufficient to reach a target mash pH. Malts are tested with a procedure called a congress mash, which is a very standardized process using deionized water. The mash pH for base malts generally settles at 5.8–6.0, which gives an indication of what other acidification is necessary when brewing.

If you are using RO water, mashing base malts should result in a fairly consistent pH that you can measure and use as part of your recipe planning. I recommend using a good-quality, calibrated digital pH meter for this purpose. You can then measure how much acid you need to add to your mash to lower the pH to the desired range. Use your pH meter to monitor the pH change, and record the amount of acid needed.

I acidify all my RO brewing water to a pH of 5.5, which is a trick I learned years ago at Sierra Nevada’s Beer Camp. This prevents tannin extraction during sparging and also helps me prepare for mashing. Even if you handle your mash pH calculations differently, I recommend acidifying your sparge water and keeping the temperature below 176 °F (80 °C). If you don’t acidify your mash with (liquid) acids, you may find that you need to add 2–3% sauermalz (acidulated malt) to your grist to achieve your desired mash pH.

When I brew, I try to have consistent mash performance every time. So, I tend to only mash base grains and starchy adjuncts — things that actually need to be mashed. I leave out roasted and crystal malts from the mash since they are already converted. I add these grains during wort recirculation, after the mash is over. The pH during the mash thus becomes very predictable without the use of recipe software or water calculators. 

If you do include crystal malts and roasted grains in the mash, you may need to use the water calculators to adjust your mash chemistry and reach a desirable pH. The mash pH should settle within the first 10 or 15 minutes of the mash, so that’s when the pH can be tested (by first cooling a small sample to room temperature). 

With my process, I stopped measuring mash pH because it was always where I expected it to be. With good process control and consistent use of ingredients, that kind of performance is possible. I occasionally spot-check the pH of my mashes, but that’s more like performing a random audit than a process control.

Not all salts in the mash carry over to the boil (one source estimates it at 40–60% of salts are filtered by the mash). If the final mineral profile is important to the flavor of the beer style being produced, I will make another addition of salts to the kettle.

My Method for Water Adjustments

There are a wide variety of salts, acids, and bases that can be used in brewing, but I find that I use a very limited subset when using RO water. Many of the options are redundant, or only useful in specialized situations. Others have side effects that I would rather avoid.

The three most important additives for me are:

Calcium chloride (CaCl₂) — Adds calcium in the most flavor-neutral way. Chloride adds a soft, wet, round, fat, sweet, or full impression to beer that often favors malty styles.

Calcium sulfate (gypsum, CaSO₄) — Adds calcium but also sulfates that may have a negative flavor impact with noble-type hops or cause a harsher, sharper bitterness.

Phosphoric acid, 10% solution — My primary way of adjusting acid in the most flavor-neutral way. Using the more dilute solution makes it safer and easier to handle, as well as measure.

I generally don’t want to add magnesium due to its laxative and souring effects, but if I did, I would use Epsom salts (magnesium sulfate). Likewise, I rarely want to add sodium due to its blood pressure effects, so I avoid using kosher salt (sodium chloride) and baking soda (sodium bicarbonate) (admittedly, the amount of sodium that would be added to beer is minimal, but I still try to avoid unnecessary sodium additions). If I did want to raise mash pH for some reason, I would use either pickling lime (calcium hydroxide) or potassium hydroxide, but these can be a bit dangerous to handle. Lactic acid can also adjust pH like phosphoric acid, but the flavor can mimic beer faults (generally not in the concentration used to adjust pH, however).

I can perform my measurements with two or three instruments: A good set of kitchen measuring spoons, a digital pH meter, and a TDS meter. These, plus a hydrometer or refractometer, and a quick-read digital thermometer, are my basic brewing instruments I keep handy.

I start by checking my source RO water with a TDS meter. If it reads low, I know it is really RO water and will respond as I have tested. If not, I know that I have to take additional readings and possibly adjust my measurements.

I then adjust all my brewing water with phosphoric acid to pH 5.5 at room temperature. I use a pH meter the first few times I do this to measure how much I am adding. For my water, it’s about 1⁄4 tsp. per 5 gallons (19 L) of RO water. But you should measure and test your own water. It’s important.

This brewing water is then used for mashing, sparging, and whatever other utility tasks I have, such as cleaning.

I measure water salts I am using in my recipe using a teaspoon. These salts are added to the mash, not the hot liquor. I generally add the milled grain, then the salts, then underlet my mash with the hot liquor. Measure your mash pH about 10 minutes after you have mashed in. If it’s off, wait another five minutes and try again. Only then consider making adjustments (which is something I almost never do).

Some recipes may use kettle salts (for example, I might add some calcium sulfate during the boil to adjust the flavor profile of English IPAs without overly affecting the mash chemistry), but this is a distinct minority of brews for me.

Water Profiles

When I first began brewing, many recommendations involved creating water profiles based on classic brewing cities that were associated with certain beer styles. There are several problems with this approach, however. First, is accuracy — are the profiles actually representative of the cities? Did they come from the sources used by breweries, or are they simply local to the area? Are they from modern times or from when the styles were developed? 

Second, are those profiles actually what brewers used? Did the brewers perform any pre-treatment? Is it the profile of what is in the mash tun? I don’t think so. Even the premise of famous cities and styles makes no sense in some cases. Consider Munich, London, and Edinburgh. What styles originated there? Munich dunkel or helles? London brown or porter, or bitter? Scottish wee heavy or IPA? Those styles require very different water, yet are from the same cities.

Finally, the profiles often don’t make sense from a chemistry standpoint. They are either incomplete or could not exist at typical water pH ranges. This is probably because multiple sources of data were averaged or that numbers were just made up. Either way, they often don’t represent actual targets.

However, generalities about the local brewing water in classic brewing cities is relevant and often does inform choices — just not at the level of precision that published water profiles imply. Statements like, “Pilsen has low mineral water” or “Burton has high sulfate water” are useful for understanding the historical basis for styles.

I don’t really have a library of water profiles for each style of beer, rather I have some general guidelines. I tend to think of beers by their major characteristics and then decide if I want to accentuate certain flavors through the use of flavor ions. The nice thing about this approach is that the flavor ions can also be added to the finished beer. So, if you aren’t sure about the flavor profile you want, you can run some tests with your completed beer and decide what you want to incorporate into your next batch. Just run those tests as bench trials on a small glass, not a full keg, and scale up when you find what you like. Here are my general guidelines:

• For most beers, I use one teaspoon of calcium chloride per 5 gallons (19 L) of finished beer. This should provide about 60 ppm of calcium and 107 ppm of chloride, per Korzonas’ Homebrewing: Volume 1. I find this provides ample calcium for the mash, and allows the flavors of the beer to come through cleanly.

• For some hoppy styles (like pale ales), I instead use one teaspoon of calcium sulfate per 5 gallons (19 L) of beer. This provides about 59 ppm of calcium and 141 ppm of sulfate, per Korzonas.

• For some more balanced styles (like Kölsch), I’ll use a half teaspoon of both calcium chloride as well as calcium sulfate. 

• British beer tradition often mentions the ratio of sulfate-to-chloride, so I sometimes will try to play with the ratio while keeping the total quantity of salts to about a teaspoon. Briggs recommends sulfate:chloride of 2:1 to 3:1 for Burton ales and 2:3 for mild ales, for instance. West Coast-type American IPAs use a lot of sulfate, but New England-type IPAs favor chlorides. Think about the difference in how those beers finish to give you an idea of the range of adjustment.

• If I’m making a beer style that is known for a minerally profile, like Dortmunder export or English IPA, I’ll double the level of salts — 2 tsp. per 5 gallons (19 L), using half of them in the kettle and half in the mash. I’ve tried making IPAs with high amounts of sulfates and I just don’t like the flavor as much as I do with less. Your palate might think otherwise.

• If I’m brewing a Czech Pilsner or other very low mineral beer, I’ll halve the standard amount — 1⁄2 tsp. of salts.

• I try to avoid using sulfate salts in conjunction with noble hops, because it creates a clashing flavor to my palate. 

• I often rely on yeast nutrients to provide trace elements for fermentation; I don’t try to add those directly. I prefer Wyeast brand yeast nutrient.

These additions assume that you are following the process I have outlined in this article — that you have treated your RO brewing water to pH 5.5 with phosphoric acid, and that you are adding your crystal malts and dark grains after the mash has finished. If you follow other processes, you will have to account for adjustments needed to hit your target mash pH.

Remember that you can adjust flavor ions after the beer is finished, as well as the finished pH. Lower pH makes the beer thinner and sharper, higher pH makes the beer rounder and fuller. Finished beer pH shouldn’t be above 4.5 in order to protect it against infections. I don’t think these post-fermentation treatments are normal; however, I sometimes use them to play “what if” games and think about future recipe development. It does help you fine-tune a recipe to your test, and could help put the finishing touches on your competition beers too.

I can’t stress enough how important it is to taste your beer. Not drink it — taste it. Think about it like a judge. Are you tasting minerals or the ingredients? If it tastes too minerally, make adjustments in future batches. How is the finish? Is it too sharp or too flabby? Adjusting the amount of chlorides and sulfates can help soften or sharpen the beer. Experimentation on a very small scale with your finished beer helps you avoid brewing many larger test batches.

It’s interesting; while researching different author’s positions on water additions, I found a quote in Dave Miller’s Homebrewing Guide from 1995, “One tsp. of either CaCl₂or CaSO₄ is the most you should need (per 5 gallons/19 L of mash water).” So it seems I wasn’t the first to make this observation. I’m in good company.

On Measurement

I’m an engineer, so I’m comfortable with judicious use of approximations. There is a point where good enough is, well, good enough. Adding extra precision doesn’t always give you better results; it just consumes time and distracts you from important tasks. Fiddling with water is one area where this extra precision doesn’t add significant results.

Yes, using volume measurements for water salts is less precise than weights. But what does that extra precision buy you if your other quantities are unknown or are approximates themselves? If your source water is unknown, why add a highly precise addition? If your target profile is at best a guess, why must you hit it exactly?

I trust my palate to tell me when my beer is good, not an equation. And I know a volume measurement is a reasonable approximation of a weight measurement in normal brewing conditions.

Final Thoughts

Brewers made great beers for hundreds of years without gram scales or spreadsheets. You can too. RO water is the key to not worrying about precise water adjustments. Embrace the elegance of simplicity, and begin enjoying the fruits of your labor.

I would like to acknowledge the teachings and friendship of A.J. deLange over the past 20 or so years, and all that he has done to further the understanding of water. He helped me understand the science behind the practical observations that I made about brewing and to validate my methods.

Written by Gordon Strong