Lately my beers have been cloudy and had a slight sour note to them. Of course I suspected an infection, and I went to the usual extremes to eliminate any possible source. With no result.
Then I realized that this problem started when I got in a new batch of malts. Could there be a lactic acid bacteria infection in the malt, thus producing lactic acid in or on the malt which was then carried forward (as acid, not as a bacterial infection) into the mash, the boil and the fermenter respectively?
So I decided to do some pH measurements on my various malts (at least the ones used in the problem beers). And I got some weird results.
I took 50 grams of each malt, crushed it (using mortar and pestle, cleaned between malts so as to avoid cross-contamination, rather than the usual malt mill) and steeped them in 150ml of water at a starting temperature of 70 degrees. (Obviously i'm not overly concerned about mash efficiency, enzyme health or tannin extraction here). Then a quick stir with a clean plastic spoon, and a pH measurement using indicator strips.
My water comes through a borehole (well) from a limestone layer at about 30m depth, and is therefore rather alkaline. I measured the pH of the water as well.
I measured the following pH values:
- Water (same sample used for strike water) - 6.2
- Pale malt (American 2-row, imported as barley and malted locally) - 5.8
- Crystal 60L, imported from Germany (Weyermann's maltings) - 4.5
- British Crystal 95-115, imported from UK (Baird's maltings) - < 4.5*
- Black patent malt 525L (produced locally) - 5.0
* (indicator colour was off the scale, indicator package did not show colour indicating pH lower than 4.5)
Give the fact that I have used Baird's crystal extensively, that's the first one I might want to change to see if that's the problem. I should also note here that the origin and age of the various imported malts are not known to me, so they could very well be dodgy - I'm in Africa after all.
Now the water sample and the pale and black malts look more or less like what I would expect. What I cannot explain is the weirdly low pH value on both the C60 and the British crystal. Yes, both are imported, but from different sources. One could be dodgy, but two? The literature I have seen suggests that the pH of crystal malts should be somewhere between that of pale and black malt.
What could be going on here?