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Dark Malts and their Effects on Mash pH

If you’re striving towards consistently great homebrewed beer, then accurately monitoring the pH throughout the process can give you a greater level of control and help you perfect your brews. Dave who works in our UK office has been exploring this area and shares below an experiment he conducted looking at the effects of dark malts on your mash pH:
Recently I was inspired by an old article in Zymurgy titled; ‘Nanomashing: Investigating specialty grains on a small scale’. The basic idea is taking a small amount of grains and water and performing a minute scale mash which will provide you with a tasting sample of the grains you are using. It seems like this could be a really useful tool for homebrewers when developing recipes to get a sense of the contribution of each type of grain.
Not only is this useful for getting an idea of the flavour contribution of your speciality grains, but you can experiment with things like water chemistry to get a better understanding of mash pHs and the effect different grains have on this.
In particular I was interested in using nanomashing to measure the pH change caused by adding dark malts. Dark malts are naturally acidic and so adding them to the mash causes the pH to drop. This can be problematic for brewers when making beers with a large proportion of dark malts (such as stouts or porters for example) as low pH can cause difficulties in terms of poor enzyme activation and filtration issues. When brewers try to correct the pH change, salts such as bicarbonate of soda are effective at raising the pH but large additions can raise your sodium levels above the acceptable brewing levels – which can just as easily ruin your beer as a low pH!
It would be interesting to know then, how significant the drop in pH from different varieties of dark malts? Are some more acidic than others? I decided to experiment by nanomashing different dark malts and monitoring the pH change in water to get an idea of which malts have the biggest effects and what those effects are.
Malts – I wanted a mixture of dark malts so went with;
  • Midnight Wheat
  • Chocolate
  • Dark Crystal
  • Carafa III
For each different grain I took 400 ml of water and 100 g of the chosen grain. I heated the water up to 67°C and let the grains soak for an hour each (effectively replicating the mashing process) taking a pH reading of the water beforehand and a pH reading after the hour long mash to see what the change was. Results are below;
Mash pH
I was really surprised by the fact that the Dark Crystal malt had as big an impact on the mash pH as the Midnight Wheat (as visually it looks a lot lighter), dropping the pH 2.8 points lower than the water measurement and 0.5 below the ideal brewing range of 5.2 – 5.5. I was expecting the darker malts like Carafe III to have the most pronounced impact but this experiment highlighted something I wasn’t aware of when brewing and that was crystal malts high acidity, which in some cases is higher than roasted malts.
As part of the nanomashing I also tasted a little of the wort I’d created to get a sense of flavour contributions from the different grains;
Midnight Wheat: Really nice, almost smokey aroma but extremely acrid, almost ash, burnt flavour.
Chocolate: Nice burnt toast aroma, bitter with a slight maltiness. No chocolate in taste or aroma.
Dark Crystal: Scorched toffee aroma with a burnt, malty taste.
Carafa III: Heavy toast and chocolate aroma with an acrid, burnt taste.”
As you can see, nanomashing is a great way to do small scale experiments that really give you a sense of the ingredients you’re using and their effect on your beer and brewing process and is well worth a go at home.

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