Magnesium is a critical part of brewing beer and without it your yeast can’t ferment. But with too much, your beer can develop an unpleasant bitter flavor.

What is the role of Magnesium in brewing?

Magnesium is an essential nutrient for yeast growth and metabolism, giving it a better fermentation rate. But most of the magnesium that you need won’t come from your water, but your grain.
Because it is easy to overdo Magnesium and get an overly bitter flavor, many older brewing guides suggest never adding magnesium and trying to minimize it in your water, but this isn’t always the right decision.

The science of Magnesium amounts in your brewing water

Let’s break down the numbers to show you why you don’t always want to minimize your starting Magnesium.
Many commercial beers have 60 to 150 ppm of Magnesium as a final product.
*ppm is approximately the same as mg/L.

From the grain itself you’ll get around 50-90 ppm extracted.
Water sources can vary wildly, from having 0 ppm from some filtered waters, to having over 150 ppm in some hard waters.
This means if don’t know your water’s starting Magnesium level and it is near 0 ppm, and your wort ends up only producing 50 ppm, your beer will be on the lower end of the recommendations. If you are producing a beer with lower ABV and low bitterness, this won’t be an issue.
But if you want to brew something like an imperial IPA, you’ll need higher levels of Magnesium to bring the natural bitterness out of the hops, and to help the fermentation process produce higher levels of ABV in your finished beer.

How to Measure your Magnesium levels

Because the grain will produce an unknown amount of Magnesium (50-90 ppm approximately), the factor that we can measure is the water itself. If we are wanting to replicate a water profile that has lower levels of Magnesium, we want to make sure that our water is closer to the 0-20 ppm level.
But if we are wanting a water profile that will create a more bitter brew like an IPA, we’ll want our Magnesium levels closer to the 30-40 ppm level.
The only way to know your magnesium levels is to test your water. With Craft Pro we offer two methods to test, DIY Test Strips or In-Lab.

DIY Test Strips

The Craft Pro DIY Test Strips will give you an easy, affordable way to measure Magnesium with each batch. These will measure Magnesium along with Hardness, Calcium, pH, and several other key factors for your brew.

The test strips will give you results in a range, meaning you will know if your Magnesium is 0-10 ppm, 10- 20 ppm, etc.

Craft Pro In-Lab

The In-Lab Craft Pro Test Kit will allow you to send a water sample to our EPA-Certified lab and get exact concentrations for your brewing water or any brewing liquid.
You will know exactly what your Magnesium concentration is. You can also test your water before and after brewing, to see how much magnesium is coming from your grain and the brewing process to adjust levels for future batches.

How to Lower Magnesium levels in water to brew beer

If the Magnesium levels in your water are too high, there are a few options to reduce it. One is to cut your water source with distilled water in whatever ratio you need. For example, if your levels are 40 ppm and you wanted 20 ppm, you can cut it 1:1. Just remember that this will reduce all of your mineral levels, not just the Magnesium.

Another option is to use softened water. A water softener will remove Magnesium and Calcium as well as reducing total hardness. The negative of using softened water is that it may add sodium, and you aren’t controlling how much Calcium and Magnesium gets removed. Some sodium in your water is fine, but you don’t want to end up with a salty beer.

Reverse Osmosis to remove Magnesium

A lot of brewers with harsh water prefer to use a Reverse Osmosis (RO) system to filter their water through. The benefit of an RO system is that it will take your water to a blank slate if adjusted correctly. Meaning you can very specifically add back in exactly the mineral composition that you want, creating a very consistent profile to work from.

One problem when using RO water is that sometimes your RO water is not as “pure” as you would think. You still need to test your water to make sure you truly are working from a blank slate before adding minerals back in.

This will require you to add back in the minerals that you need to match the style of beer you are brewing.

There are several apps and online calculators that can help you plan your water profile and tell you exactly what to buy, and how much to use.

How to raise Magnesium in your water for brewing

There are two main methods of adding Magnesium to your water and they are Magnesium Chloride (hexahydrate MgCl2•6H2O) and Magnesium Sulfate (heptahydrate MgSO4•7H2O), commonly known as Epsom Salt.
Both will do the same thing with one main difference. Magnesium Sulfate will also increase the Sulfate levels of your water, so if you need low Sulfate levels or are already at your desired levels, Magnesium Chloride can be used instead.
For either one, make sure you are ordering food grade. There are a lot of Epsom Salts on the market, and most aren’t food grade or have other additives.

Conclusion:

Because of the variability in your grain and yeast, it may take some experimentation to get your water levels exactly where you want them not only with your Magnesium, but with all your water parameters. But knowing your starting point will help you make an informed decision on if you need to adjust your water or start with another source and build your own water profile.