The Influence Of Grain DI pH On Mash pH

Distilled water, or highly purified water such as reverse osmosis water, are deficient in minerals such as calcium and magnesium. Because of the mineral deficiencies distilled water has zero alkalinity. It lacks the ability to resist pH change, it has zero buffering capacity. In the mash, grain introduces acid buffers that change the pH level of the mash. Lighter colored malt has a pH buffer value near pH 5.8 and darker colored malt has a pH buffer value near 4.7.

The optimal mash pH range required to ensure the most effective enzyme conversion in the mash, and the most efficient hop utilization in the boil, is in the pH range from 5.3 to 5.5. Brewing water used in the mash should be buffered in a way that will enable it to overcome the acidic buffer introduced by the grain. The acid and mineral levels of excellent brewing water provides enough alkalinity to hold the mash within the optimal pH range of 5.3 to 5.5.      

What Happens In The Mash?

What is DI pH and why is it important? The term DI pH is derived from the word distilled as in distilled water and pH as in pH value. You can determine the DI pH value of any grain by finely crushing 40 grams of grain, mixing it in with 100 milliliters of distilled water and then heating the resulting mash to 125°F for 20 minutes. A pH reading taken of the resulting wort when cooled to 77°F is the DI pH value of the grain. Various grain types, and sometimes the same grain type sourced from several maltsters, will have different DI pH values. Accurately calculating brewing water adjustments to optimize enzyme activity in the mash is largely dependent on knowing the correct DI pH value for each grain.

What happens in the mash tun during the mash? The mashing process can simply be stated as 'a mixture of grain and water, heated to a temperature of 149°F to 155°F in order to trigger the enzyme conversion of starch to sugar'. But there is more to it than that. The ratio of grain to water commonly referred to as the mash thickness, also affects the efficiency of conversion. It is a combination of mash temperature, mash thickness and pH that have an affect on mash efficiency.

• To calculate mash efficiency take a hydrometer reading of the pre-boil wort volume, drop the decimal point then subtract 1000 from the reading, Next multiply that number by the pre-boil wort volume in gallons and then divide that number by the total pounds of grain in the recipe.
• Example: With a pre-boil gravity of 1.048, dropping the decimal point and then subtracting 1000 equals 48. Multiplying 48 times 13 gallons of pre-boil volume equals 624. Dividing 624 by the 23 pounds of grain used in the recipe equals an extract efficiency of 27.1 

It is important to point out that the conversion of starch to sugar becomes much more efficient when the pH of the mash is between 5.1 and 5.3 at mash temperature. The same mash sample when cooled to 77°F measures between pH 5.3 to 5.5, something to keep in mind when referencing mash pH values.

The DI pH Values Differ Between Grain Types

How does the pH and the temperature of the mash influence my beer? Alpha and beta amylase enzymes in the mash convert starch into non-fermentable and fermentable sugars. The alpha amylase enzyme breaks down starches into glucose (dextrins), producing non-fermentable sugars that add fullness and body to beer. The optimal temperature range for the alpha amylase enzyme is between 145°F to 158°F and the optimal pH range is between 5.3 to 5.8.

The beta amylase enzyme breaks down starches and sugars into maltose, producing the highly fermentable sugars that are preferred by yeast the most. The optimal temperature range for the beta amylase enzyme is between 131°F to 149°F and the optimal pH range is between 5.0 to 5.6.

Test Mash Sample Used To Record Grain DI pH

A 149°F mash is will produce wort that makes a thinner, drier, higher alcohol beer. A 155°F mash produces a wort that makes a maltier, sweeter, fuller bodied beer. To a somewhat lesser extent a mash pH of 5.5, favoring the alpha amylase enzyme, will produce a less fermentable wort. Where a mash pH of 5.2, favoring the beta amylase enzyme, will increase the fermentability of the wort.

The available window of opportunity for a brewer to influence the fermentability of their wort is very narrow. Mashing at temperatures lower than 149°F, or higher than 155°F, will cause enzyme activity to slow down considerably resulting in a decrease in conversion efficiency.

Enzyme activity slows down when the mash pH falls below 5.1, or rises above 5.3 at mash temperature, resulting in a decrease in conversion efficiency. Mash temperatures or pH values that fall too far outside of their optimal range, change the shape of the enzymes causing them to become denatured, which reduces their ability to convert starch to sugar.     

Brewing Water Accuracy Is Dependent On The DI pH Value Of The Grist

Why is it important to know the DI pH values of the grains used in the mash? On average when grains are mashed using reverse osmosis or distilled water, the pH of the mash ends up in the 5.8 to 6.0 pH range. Lacking the buffering needed to resist pH change, distilled water will seek an equilibrium relative to the acid content of the grain, if left unchecked. It is important to point out that a mash pH of 5.8 to 6.0 is well outside of the optimal pH range for both the alpha and beta amylase enzymes.  

The acid content of different grains will vary from grain type to grain type and from maltster to maltster, even when they are producing the same type of grain. The acid content of a roasted malt can have a DI pH of 4.71 and the acid content of a pilsner malt can a much higher DI pH of 5.75. It is also true that 2-Row malt produced by Rahr can have a stated DI pH value of 5.56 while a 2-Row malt produced by Briess can have a DI pH value of 5.70. Some maltsters provide inaccurate information regarding the DI pH of their grain while other maltsters provide no information at all, which confuses the interpretation of DI pH values even further.

Testing Grains For Their DI pH Value Is Worth The Effort

Determining the DI pH of any grain can be accomplished by crushing 40 grams of malt and then stirring in 100 milliliters of distilled or reverse osmosis water to produce a 1.2 qt/lb ratio mash. Allow the mash to reach equilibrium by letting it settle for at least 20 minutes. During this time the pH of the mash will change. The darker the malt is the higher its acid content and the lower the pH value will be. Conversely the lighter the malt is the lower its acid content and the higher the pH value will be. Use a recently calibrated pH meter to take a reading of the test mash and then record the pH value as the DI pH value of the grain tested.

Just enter the DI pH values of grains that have been tested into ezBrewingWater-RO© and be confident that your brewing water profile has been accurately optimized for those grains when they are mashed.