Of the ions required for brewing, calcium is by far the most important. This is because of the acidifying effect that calcium has on the wort.
3Ca2+ + 2HPO42- Ca3(PO4)2 + 2H+
Wort contains large amounts of phosphates derived from the malt, and these have a buffering effect - that is they tend to mop up hydrogen ions and keep the pH higher than desired. Calcium ions precipitate phosphates as insoluble calcium phosphate and release hydrogen ions into the wort. It is worth mentioning at this point that whilst the pH of the wort is critical, that of the water in the HLT is not. The pH of water may vary from about pH 5 to pH 8 dependent upon the levels of dissolved carbon dioxide - even de-ionised water can have pH levels as low as 5 after exposure to the air. However the carbon dioxide is driven off by heat in the HLT and the pH of the water will rise.
A combination of the presence of calcium ions and the decrease in pH has a number of effects on the brewing process:
* The lower pH improves enzyme activity and thus wort fermentability and extract.
The optimum pH for ß-amylase activity is about 4·7. Wort produced from liquor containing no calcium has a pH in the order of 5·8 - 6·0, compared to values in the range of 5·3 - 5·5 for worts produced from treated brewing liquor. The activity of the ß-amylase then is greatly enhanced by the addition of calcium, this exo enzyme increasing the production of maltose from Amylose, and thus making worts more fermentable.
* Calcium has an almost 'chicken and egg' effect in the precipitation of wort proteins, both during mashing and during the boil.
Protein-H + Ca2+ Protein-Ca + 2H+
The hydrogen ions released further reduce the pH which encourages further precipitation of proteins. Proteins are also degraded, that is converted to simpler substances by proteolytic enzymes called proteases. These are found in the malt, and have optimum activity at pH values of about 4·5 - 5·0. The reduction in pH then caused by the presence of calcium encourages proteolysis, further reducing protein levels and increasing wort Free Amino Nitrogen levels (FAN). FAN compounds are utilised by the yeast during fermentation for the manufacture of Amino acids, and an increase in FAN levels in the wort improves the health and vigour of the yeast. High protein levels in beers also have negative effects, making beer more difficult to fine and encouraging formation of hazes, in particular chill hazes. Product shelf life can also be adversely affected.
* Calcium ions protect the enzyme a-amylase from inhibition by heat.
a-amylase is an endo enzyme, cleaving the internal 1,4 glucosidic links of amylopectin resulting in a rapid reduction in wort viscosity.
It can be seen then that the presence of calcium has positive effects on the activity of both a-amylase and ß-amylase, two of the most important enzymes in the brewing process.
* The drop in pH encouraged by Calcium ions in the mash and copper helps afford the wort and subsequent beer produced a greater resistance to microbiological infection.
* The reduced pH of the sparge liquor reduces extraction of undesirable silicates, tannins and polyphenols from the mash bed.
The extraction of such materials is encouraged by alkaline sparge liquor. These materials are very undesirable, contributing to harsh flavours, hazes in the finished beer and decreased beer stability.
* Calcium precipitates oxalates as insoluble calcium oxalate.
This again occurs in both the mash tun and the copper. Oxalates cause hazes in finished beers and also contribute to the formation of beerstone in FV's, CT's and casks. Oxalates are also thought to promote gushing in certain beers, although this is not generally a problem to the micro brewer.
* The presence of calcium reduces colour formation in the copper.
This is due to the reduction of extraction of colour forming compounds such as anthocyanogens and pro-anthocyanidins during the sparge. The reaction: Reducing Sugar + Heat Melanoidins is also inhibited.
* Calcium ions improve beer fining performance.
Calcium ions encourage yeast flocculation - being a divalent Cation it has a natural affinity for negatively charged yeast cells.
With all the above advantages of the presence of calcium and reduction in pH there is one minor disadvantage.
* The reduction in pH causes a decrease in hop utilisation, giving less bitter beers.
This increases hopping costs, since more hops will be required to achieve a desired level of bitterness. However the optimum pH for hop isomerisation as used in the commercial production of isomerised hop extracts is about pH 10, so a reduction from pH 5·8 in a mash with untreated liquor to pH 5·1 out of copper for a treated brew is not too critical.
You will see that much of the calcium added to the mash is lost - precipitated out as phosphate, proteinate or oxalate. Since calcium is specifically required in the copper for further precipitation of these materials it is common to add calcium to the grist or Hot Liquor Tank and to then make a second addition to the copper. Where this is not practical it is quite acceptable to make a larger addition to the grist or to the H.L.T.
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