exBEERiment | Water Chemistry: Impact Increasing Mash pH With Slaked Lime Has On An Oatmeal Stout

Author: Will Lovell

“If your water is good enough to drink, it’s good enough to brew with.” The popularity of this age-old trope appears to be trending downward, which makes sense considering water is the most prominent ingredient in beer. In addition to mineral content, brewer’s often focus on mash pH, which is widely believed to positively impact conversion efficiency, fermentation, hop extraction, and clarity of the finished beer when in the ideal range.

Acidification of the mash is common in paler styles, though beers made with higher proportions of roasted grains often require the use of an alkali to increase pH, as the roasting process breaks down carbohydrates and proteins into acids. Commonly referred to as either slaked or pickling lime, calcium hydroxide is one such alkali used for this purpose, as it’s easily accessible, inexpensive, requires very little to be effective. Moreover, outside of the benefits believed to come with proper mash pH, slaked lime isn’t believed to have much if any impact on other beer characteristics when used properly.

While two past xBmts have shown that fairly drastic mash pH differences didn’t produce beers that were perceptibly distinguishable, they were both focused on paler styles. This left me wondering if adjusting the mash pH of a notably dark beer with an alkali might produce a different result. My alkali of choice being slaked lime, I keep plenty on-hand, and with an Oatmeal Stout on deck, I designed an xBmt to test this one out for myself.

| PURPOSE |

To evaluate the differences between an Oatmeal Stout where the mash pH was left unadjusted and one where the mash pH was adjusted up with slaked lime.

| METHODS |

For this xBmt, I went with an Oatmeal Stout recipe that was based off of past successful batches I’d brewed.

Mighty Is The Groat

I started this brew day by adding identical volumes of water to separate Delta Brewing AIO units and adjusting each to the same mineral profile with one exception – I added slaked lime to one batch, the amount of which was determined based on Brewfather calculations to achieve a 5.6 mash pH.

While the waters were heating up, I weighed out and milled the grain.

When the water for each batch was adequately heated, I incorporated the grains then set the controllers to maintain them at the same mash temperature.

At 20 minutes into each mash, I took pH measurements that objectively demonstrated the impact of the slaked lime addition.

While the mashes were resting, I prepared the kettle hop additions.

Once each 60 minute mash was complete, I removed the grains and proceeded to boil the worts for 60 minutes, adding hops as listed in the recipe.

When the worts were done boiling, I took refractometer readings showing they were at the same target OG.

I transferred identical volumes of wort to Delta Brewing FermTanks that were attached to my glycol system and left to finish chilling to my desired fermentation temperature. Within 20 minutes, both worts were stabilized at 66°F/19°C, so I pitched a pouch of Imperial Yeast A09 Pub into each.

With signs of activity absent 2 weeks later, I took hydrometer measurements showing the beer where slaked lime was used for mash pH adjustment attenuated slightly more than the non-adjusted batch.

At this point, I cold crashed the beers overnight before transferring them to CO2 purged kegs that were placed on gas in my freezer. After 2 weeks of conditioning, the beers were carbonated and ready for evaluation.

| RESULTS |

A total of 22 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the beer that was not adjusted with slaked lime during the mash and 1 sample of the beer where the mash pH was adjusted with slaked lime in different colored opaque cups then asked to identify the unique sample. In order to reach statistical significance, 12 tasters (p<0.05) would have had to accurately identify the unique sample, though just 8 did (p=0.46), indicating participants in this xBmt were unable to reliably distinguish an Oatmeal Stout where the mash pH was not adjusted with slaked lime from what where slaked lime was used to increase mash pH.

My Impressions: Out of the 5 semi-blind triangle tests I attempted, I correctly identified just once. Despite the slight difference in attenuation and thus ABV, these beers were perceptibly identical to me, both having a nice roast character with medium-low dark chocolate and a deliciously creamy finish.

| DISCUSSION |

Over the last decade or so, brewers seem to have come around the idea that water chemistry matters, at least more than many were originally led to believe. Included under this rather broad umbrella is mash pH, which is widely believed to positively impact both objective and subjective aspects of beer. Interestingly, tasters in this xBmt were unable to reliably distinguish an Oatmeal Stout where the mash pH was not adjusted with slaked lime from what where slaked lime was used to increase mash pH.

The commonly accepted ideal range for mash pH is 5.2 to 5.6, which also happens to be where most beer recipes tend to fall with no water chemistry adjustments, assuming decent water is used. Indeed, the non-adjusted batch in this xBmt ended up being 5.2 whereas the batch adjusted with slaked lime was at 5.6. While this difference on its own is certainly notable, both were within the accepted ideal range, which may explain why tasters couldn’t tell the beers apart.

Considering these results in light of past xBmts on mash pH, it’s looking more and more like this particular variable may be more important for process efficiency while having minimal perceptible impact. Even so, the beers differed by just 0.4% ABV, which just isn’t enough for me to justify continuing to worry about mash pH adjustments. I’m not saying I’m going to stop paying attention to mash pH altogether, as it’s easy enough to keep track of in Brewfather, I’m just no longer convinced it’s as consequential as I once believed it to be.

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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