Mash pH, is it that Important?

It is represented by just two letters but the importance of the pH in a homebrew mash cannot be understated.  However, I would argue that for many of us pH barely appears on our home brewing horizon.  But should we be paying more attention to the mash pH?  Does a better understanding and control of pH, especially during mashing, allow us to gain a better control over the composition of our wort?  In this article I will try and define what the pH is, why it matters in mashing and how we can try and manipulate it.  Before I go on I would add that using water direct from the tap is perfectly acceptable and will produce great quality home brewed beers.  Therefore if you are not bothered by controlling your mash pH then you would be better off skipping this article.

The first thing to do is to answer the question, what is pH?

The pH of a solution is a measure of the solutions acidity or alkalinity.  The pH scale runs from 0 to 14 with 0 being very acidic, 14 very alkaline and 7 neutral.  The pH scale actually measures the concentration of hydrogen ions (H+) in solution.  Thus a highly acidic substance will release H+ ions when in aqueous solution.  For example if you consider hydrochloric acid (HCl) it is highly acidic because it more or less completely dissociates in water to give H+ and Cl ions.  To better understand the range of the pH scale it is perhaps useful to be able to define where on the pH scale some everyday household items sit.  Therefore if you consider that pure water is neutral at pH 7, then lemon juice is acidic at around pH 2 and something like milk of magnesia is alkali at around pH 10.5.  Beer is acidic as is the wort that it is made from however during the brewing process the pH actually drops as wort is fermented into beer.  Thus the normal mash pH is approximately 5.4 – 5.9 and beer can be anywhere between pH 3.8 – 4.5.

Why is pH so important in home brewing?

The pH of a solution is highly critical if there are biochemical reactions that are going on in that solution.  For example the breakdown of malt during mashing, and especially the conversion of starch into simple sugars, relies on enzymic activity and the activity of those enzymes is defined by, amongst other factors, the pH.  If we consider the two main starch degrading enzymes alpha and beta amylase the pH optimum, that is the pH at which the enzymes work most efficiently, is pH 5.5 for alpha amylase and pH 5.2 for beta amylase.  Bear in mind the typical mash pH can be anywhere between 5.4 and 5.9.  Therefore if you alter the pH of your mash you can potentially alter the conversion of starch to simple sugars and by definition wort fermentable sugars.  Some commercial brewers go as far as to acidify their mash to optimise the performance of the amylases and thereby improve the conversion of starch to simple sugars.  The table below clearly demonstrates the impact of pH on the conversion of starch into simple sugars.  As the mash pH drops the percentage of maltose present in the resultant wort increases giving a more fermentable wort.

Mashing TemperaturepH 4.5pH 5.3pH 5.6
65ºCMaltose 64%
Dextrins 20%
Maltose 62%
Dextrins 22%
Maltose 61%
Dextrins 23%

(data reproduced from Home Brewing The CAMRA Guide by Graham Wheeler)

What determines the pH of your mash?

A brewer’s mash is a very complex mix of water and grain material and therefore the biggest determinant of mash pH is unsurprisingly the malt and water that you use to make the mash.  The question is by how much does the malt and water impact on mash pH.  To try and answer that question and in the name of home brewing science I thought it would be a great idea to carry out a few simple experiments in the form of a number of mashing trials.  The trials involved mashing with two different malt types, a pale lager style malt and a wheat malt.  I also conducted some mashing trials with water with different ionic compositions to test out the impact of using de-ionised water and water high in calcium sulphate or calcium bicarbonate.  The results of these mashing trials are illustrated in the table below.

Malt TypeWater SpecificationMash pH
Lager MaltDe-ionised5.94
Wheat MaltDe-ionised6.10
Lager MaltHigh calcium carbonate6.39
Lager MaltHigh calcium sulphate5.54

The first interesting thing to note is the impact on the mash pH of the raw material being mashed.  This is something I had never really considered before but is perhaps not too surprising.  But the results show that using a mash produced from 100% wheat malt gave a pH of 6.10 compared to pH 5.94 for standard lager malt.  A brief search of the brewing literature highlights that using high coloured malt such as black and chocolate malt will lower the mash pH.  It is therefore worth bearing in mind that the choice of malt and other raw materials will have an impact on your mash pH.  But I don’t want to be constrained as to the raw materials that I use in my brewing so I am not going to worry too much about this result.

However, the most important contributor to mash pH is the ionic composition of your brewing water.  Unsurprisingly water high in bicarbonate gives a higher mash pH and water high in calcium sulphate a lower pH.  We have written a brief article on the impact of water entitled the home brewers guide to water and how it affects the pH during brewing which is worth a read.  What must be borne in mind is that it is not the pH of your water but the presence of particular ions in your water that will have an impact on your mash pH.

How can we as home brewers manipulate the mash pH?

Most of us will use the water that comes straight out of our tap for our home brew, and there is no problem with this.  However, if we want to gain better control of the mashing process then perhaps we should be taking a closer look at what the water is doing for our brewing.

If you live in an area where your water is naturally high in calcium sulphate and low in calcium carbonate then congratulations you have got water ideal for home brewing.  However, if like me you live in an area of high temporary water hardness which is water that is high in calcium carbonate then you could benefit from a little bit of ionic manipulation.  You can do what some home brewers choose to do and brew with de-ionised water.  This water can be used as is or you can chose to add in salts such as calcium sulphate.  This is a relatively expensive method of obtaining brewing water as de-ionised water is not cheap compared to the good old water from your tap.  However, it is possible to remove temporary hardness by simply boiling your water for around 15 minutes and allowing it to stand whilst the calcium carbonate precipitates out.  You can then use this water or chose to add back things such as calcium sulphate.

The evidence is clear mash pH is a dynamic property which is influenced by our raw materials and brewing water.  By manipulating the mash pH it is possible to alter the sugar composition of your wort and therefore the flavour profile of the beers that you brew.  As I have said before the exciting thing about home brewing is that we can experiment with our ingredients to create the brewing conditions that give us great tasting home brewed beer.


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