Pre-Boil vs. Post-Boil Water Ion Concentrations
TroubleShooting
Jimmy Fortin — Montreal, Quebec asks,
I’ve been researching water chemistry for brewing and I haven’t found an answer to my question. When you are planning for the chemistry of the water, do you target the ratio of the chemistry pre-boil or post-boil? Do the minerals evaporate out of the water or do they concentrate in it? This question has been bothering me, one of your fervent readers, for a while.
This is a really good question. Water chemistry is discussed in terms of pre-mash concentrations with minimal attention given to the concentration of ions following mashing (and boil). Perhaps the primary reason for this view is that water chemistry’s greatest influence on beer is through its effect on mash and wort pH. Malt enzymes, protein precipitation in the mash and boil, extraction of malt tannins, alpha acid isomerization, and color development during boiling are some of the key brewing variables affected by the wort’s pH. However, just because water chemistry’s effect on mash and wort pH are the hot topics surrounding water does not mean that it’s the only topic.
Calcium, magnesium, manganese, and zinc are constituents found in varying levels in water, and they all have relevance to yeast metabolism. Calcium and zinc also influence yeast flocculation, giving these two compounds high priority to the practical brewer. Iron is found in some waters and can also make its way into wort from brewing equipment and even raw materials depending on growing regions and malthouse specifics (e.g., water used for steeping and iron contamination from some equipment). Iron can also be introduced to beer from filtration materials. Brewers keep a lookout for iron because it is a potent oxidizer of beer flavor.
In addition to precipitating as calcium and magnesium salts, carbonates can also decompose into carbon dioxide and water.
So, the short answer to your question is that the composition of brewing water and mineral additions is typically confined to pre-mash concentrations of the ions of interest. When wort is boiled, there is definitely a change in the concentration of substances dissolved in wort. Calcium and magnesium from water is partially lost during the boil through pH-reducing reactions with phosphates and proteins/polypeptides from malt. Some brewers add calcium to the kettle before boiling for the purpose of reducing wort pH and checking color formation during boiling. Calcium and magnesium also react with carbonates during boiling. In addition to precipitating as calcium and magnesium salts, carbonates can also decompose into carbon dioxide and water. And anything from water that does not react with wort during boiling will be concentrated by the evaporative process. Other such reactions occur that alter mineral composition during boiling.
The practical, take-home message is that brewing is a continuum from raw material production to finished beer. While the specifics about water chemistry are typically confined to concentrations of minerals in brewing water, the relevance of the topic has a much broader reach.
