Residual Alkalinity is the Alkalinity that is not neutralized by the water’s hardness. Residual Alkalinity is a brewing specific metric that helps identify if water is suitable for brewing. This is because Alkalinity is reduced by the water’s hardness at higher temperatures.
It uses Alkalinity and Water Hardness (calculated with Calcium and Magnesium) to determine how alkalinity and hardness will be affected by the mash.
Why use Residual Alkalinity and not Total Alkalinity?
Total Alkalinity is a great starting point to determine if your water is suitable for brewing. Since Alkalinity is water’s ability to resist changes in pH, many brewers try to keep alkalinity low. Typically, between 30-100 ppm.
But Total Alkalinity isn’t the whole story, it is affected by your water hardness during the brewing process. If your water has high total alkalinity but is also hard water, then you may still be able to use it when brewing. But if it has low total hardness, then it may not be suitable.
Residual Alkalinity simply gives you a more complete look at your water profile than just using alkalinity or water hardness by themselves.
What levels of Residual Alkalinity are suitable for brewing?
When brewing, the target Mash pH is always 5.2–5.4. The goal is to balance the water’s Residual Alkalinity so that the Mash pH will end up at the point, after factoring in how the mash will affect pH.
Darker and lighter beers will affect Mash pH differently, so a different level of Residual Alkalinity is needed. Light beers will aim for a lower level of residual alkalinity to reach the target mash pH. While Darker beers will need high residual alkalinity. This is because darker beers on average will have a larger impact on pH. So more alkalinity is required to stay within the target range. While lighter beers on average will have less impact on Mash pH, higher alkalinity would interfere with the mash’s ability to reach the target pH.
A good rule of thumb is darker beers will aim for Residual Alkalinity between 100 to 150. And lighter beers will aim for zero to -50. With 0 to 100 being good for many styles of beer that are medium color.
Color is not a perfect predictor of how mashing will affect pH, but it is a good starting point when determining your water profile.
How to Calculate Residual Alkalinity
There is a simple equation to calculate Residual Alkalinity, all you need to know is Total Alkalinity, Calcium, and Magnesium concentrations of your water profile.
Residual Alkalinity = Alkalinity – ((Calcium/3.5) + (Magnesium/7))
Calcium is twice as effective as Magnesium at reducing Alkalinity in your mash, though both are effective.
To get your Alkalinity, Calcium, and Magnesium concentrations you will need to have your water laboratory tested to get exact concentrations.
The CraftPro Master Brewer’s Test Kit will let you get these numbers from our laboratory but will also already have the Residual Alkalinity calculated for you.
Simply order the kit, send in your sample, and we will send you a digital report with all the water parameters you need for brewing.
How to adjust Residual Alkalinity for brewing
Residual Alkalinity can be reduced by hardening the water. Typically, this will be done by adding magnesium and calcium to your water profile. Calcium Sulfate, aka Gypsum, is commonly used as well as Calcium Chloride. Based on your target Sulfate/Chloride ratio.
Another common brewing salt is Epsom Salt, which is Magnesium Sulfate. Magnesium Chloride may also be used if you want to increase Chloride levels.
Another method to reduce Residual Alkalinity is by reducing Alkalinity. This may be done by adding acids like lactic acid or phosphoric acid.
To raise Residual Alkalinity to brew darker beers, bicarbonate can be added. This will typically be with sodium bicarbonate or by adding Sodium Bicarbonate aka baking soda.
Conclusion
Residual Alkalinity plays a crucial role in achieving the perfect mash pH for your beer. By testing and adjusting your water profile, you can fine-tune your brewing process and create better-tasting beer.
For a complete brewing water analysis, order the CraftPro Master Brewer’s Test Kit today!
