Last weekend I brewed my annual Maerzen using 75% Best Malz Vienna, 20% Weyermann Munich II and 5% CaraFoam. When designing the brewing water I went by my past experiences with a similar grain bills that used Weyermann Vienna and the surprise came when I tested the mash pH. Instead of the expected 5.5o I got 5.77. I’m generally not off by that much and was doubting the pH meter until I also tested the mash pH with colorpHast strips. During the decoction the pH fell to 5.71 and I added another 2 ml 88% lactic acid to bring it down to 5.58, which I considered ok for a Maerzen. The boil pH was later reduced as well with some lactic acid.

After testing the distilled water pH of this Vienna malt I found that is was way off from the pH one would expect from a base malt slightly darker than pilsner malt. It was 5.8. Below is a chart of the distilled water mash pH for various base malt samples that is taken from my mash pH paper:

The pH is slightly higher than pale or pilsner malts and more than 0.2 pH higher than the Weyermann Vienna that I tested a while back. This goes to show that the color/pH correlation is even weaker than I thought and that one should not rely on the accuracy of color based mash pH estimations for grists that contain a mix of base malts. The color based mash pH prediction works much better for grists made of pale/pilsner base malt and a mix of specialty malts since the pH properties of the latter are more predictable.

More predictable was the amount of lactic acid that I had to add to lower the pH. With 0.32 ml per kg and 0.1 pH drop it was well within the 0.25-0.42 ml range that I show here.

The malt analysis sheet for this batch of malt reported a pH of 5.9 for the congress mash. While I noticed this I assumed that the pH of the congress mash, which is diluted to 8 l/kg towards the end, would not be that useful for predicting mash pH. In hindsight this could have been an indication for the higher than expected mash pH.