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Why does pH matter during the boil?

pH can affect your beer in a number of ways so it is well worth paying attention to the pH of your wort at several points throughout the brewing process. We are looking specifically at the effects of pH during the boil.

One major reason that we try and control pH in brewing is to avoid excessive tannin extraction. Most of this tannin extraction will occur during the mash and sparge and mostly comes from the grain but hops also contain tannins.

Tannins are water soluble compounds that can contribute a harsh astringency to your beer. To get a sense of the effect, the drying, astringency of tea is down to the level of tannins. The plant matter of hops only contains around 2-5% tannins by weight but can contribute up to 20% of the tannins in your finished beer.

So how do you control this extraction? Well, there’s not actually that much you can do besides reducing the amount of hops that you use or else reducing plant matter in the boil. If you’re a brewer using whole hops in the boil you could consider using pellets to try and reduce tannin extraction.

Getting your boil pH right (around 5.1) also helps with the formation of hot break material. Proteins are chains of amino acids, including amino acids which try to avoid water (hydrophobic). These amino acids face towards the protein so they can react with each other rather than the water but as the protein coagulates, some of these hydrophobic amino acids will face outwards. In order to avoid water these amino acids will join with the hydrophobic amino acids of other coagulated proteins, creating larger, heavier clumps of proteins that will drop out of suspension, also taking tannins and hop material with them.

As the pH of the boil gets lower the hydrophobic sections of the proteins can react with each other more easily, meaning they clump and drop out of suspension faster. The most effective pH for this is 4.9 meaning brewers could go lower than the usual 5.2 – 5.4 boil pH in order to achieve more effective protein coagulation but this would be at the reduction of hop utilisation.

The solubility of hop iso-acids is dependent on both temperature and pH. Solubility increases with pH so by having a higher boil pH you could actually get greater utilisation of your hops and greater bitterness extraction though the bitterness extracted in higher pH boils is perceived as harsher than in a boil of normal pH (5.2 – 5.4). During fermentation, pH of your beer will drop further and this causes unisomerized hop resins to come out of suspension.

Finally, the pH during the boil can have a big effect on the colour of your beer. The higher the pH, the darker your wort will become during the boil as more melanoidins are produced. If you are looking to make a lighter coloured beer then your pH should be a key consideration.

Ultimately, if your mash pH and sparge pH have been within acceptable levels (5.2 – 5.4 for the mash and less than 6.0 for the sparge runnings) then your boil pH should land within acceptable levels too. pH drops around 0.1 – 0.2 units during the boil.

Do you measure pH throughout your brewing process or do you account for it when planning your recipes? Let us know in the comments below or by sending us an email at [email protected]


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