Continuing with a technical theme, Thom outlines the importance of calcium to the brewing process and how to calculate appropriate additions.
Calcium is essential to every step in the brewing process. Most water supplies used in brewing are deficient in calcium and additions of salts are required to increase calcium to a more suitable level. The main actions of calcium are:
It influences mash pH in a beneficial way, ensuring that the pH is kept low enough for effective mashing. This is achieved through interaction of calcium with carbonates in the water. Carbonates tend to increase wort pH, dragging it away from the optimal pH of around 5.2. Calcium binds to carbonates forming compounds that precipitate out of solution and remove the ability of carbonates to influence mash pH.
Calcium protects malt amylases against heat inactivation during the mash. Malt amylases steadily lose their ability to convert starch into simpler sugars during the mash because the mash temperature is a compromise between the optimal operating temperature of both alpha and beta amylase. Alpha amylase suffers most during the mash, but a sufficient calcium concentration protects the enzyme from heat inactivation.
During the boil trub is formed by the precipitation of protein matter through thermal degradation, but calcium plays a significant role in trub formation by neutralising protein molecules through electrostatic interactions. A minimum calcium concentration of 100 mg/l is required for good trub formation.
Yeast flocculation is aided by calcium through the interaction with proteins on yeast cell walls. Most strains require at least 50 milligrams/litre (mg/l) for good flocculation.
- Beer stone is formed from a build up of oxalate on brewing equipment. Oxalate in packaged beer provided nucleation sites for carbon dioxide that promotes gushing upon opening of the package. Values of 70 - 80 mg/l are sufficient to remove excess oxalate from the brewing process.
When making calcium additions it is important to account for the significant amount of calcium that is retained in the grain during mashing. The calcium that ensures effective mash pH is sacrificed during the acidification process in the form of calcium carbonate, a solid that precipitates and sticks to the grain. This loss can account of or 50 - 60% of the calcium in the mash.
Increasing calcium values to 200 mg/l has shown to increase run off from the mash tun, improve extraction and also increase free amino nitrogen - an essential nutrient for yeast. As the the wort gravity decreases during run off the pH tends to increase, promoting the undesirable extraction of tannins and silica from malt husks. However, it has been noted that increasing calcium in sparge water to 200 mg/l can prevent the wort pH increasing and reduces the extraction undesirable compounds.
The amount of calcium in your brewing water can be measured using test kits that are commonly used for aquarium water analysis. However, it can be assumed that most brewing water does not a have the 100 - 150 mg/l calcium that is desired for brewing. Below are some simple calculations for making calcium additions using minerals commonly used in brewing.
- The water will have a some calcium already present, though it will very likely be sub-optimal. When calculating the amount of calcium to add, the quantity of calcium in the water already must be subtracted. So that's the first step.
- This value is then divided by the percentage of calcium present in the salt you have decided to add. This value differs depending on the salt used and the extent to which water is bonded to it. Calcium sulphate has the chemical formula CaSO4.2H2O. A bit of chemistry tells us that calcium accounts for 23% of this molecule, so the value of calcium in mg/l that we want to add is divided by 0.23.
- This value is then multiplied by the litres of water that you want to treat.
The most common calcium additions in brewing water come from the following salts:
- Calcium sulphate: CaSO4.2H2O - 23% of which is calcium
- Calcium chloride: CaCl2.
Calcium chloride is very hygroscopic, which means it readily absorbs water from the atmosphere. As a result it is found in a number of forms. This influences the amount of the salt that must be added. If the molecule has two water molecules attached calcium makes up 27% of the molecule, but if has seven water molecules attached calcium makes up only 18% of the molecule. That means our numbers in the calculations in step two are 0.27 and 0.18 respectively.
An example might help clarify this:
Take some tap water with a calcium concentration of 60 mg/l. Let's say we boost the calcium to a more respectable 150mg/l, and we're brewing a stout so we should use calcium chloride to add some body.
There's 60mg/l calcium in the water already, this means we need an additional 90 mg/l to meet our desired value of 150 mg/l. Calcium chloride takes up water readily so we'll assume that your supply of calcium chloride is fully saturated with water thanks to the shoddy way you store it. This means you have:
CaCl2.7H2O - 18% of which is calcium.
You want to add 90mg/l:
90/0.18 = 500 mg/l
You have, say, 30 litres of water to treat, so:
500mg/l x 30l = 15000 mg = 15 grams of calcium chloride in 30 litres.
The scenario is the same for the addition of calcium sulphate to water used to brew a crisply hopped pale ale.
We need to add, say, 100 mg/l calcium so,
100/0.23 = 435 mg/l
And we need to treat 40 litres of water:
435 x 40 = 17391 mg = 17.4 grams of calcium sulphate in 40 litres.
As can be seen, it is easy to boost the calcium levels in brewing water, but it is important to consider that in each of the examples above addition of chloride and sulphate were also made to the water, which might result in a unsuitable balance of each of these constituents. A blend of both can help too much of either dominating, while ensuring that calcium levels are met.