I've been wanting to do a little experiment involving the mash pH of a full volume BIAB for quite some time now. The opportunity finally presented itself today and I was able to do a modified version of the experiment I had planned.
If you've read around the interwebs long enough, you've surely come across threads regarding the mash pH and how it should ideally fall within some range, lets say 5.2-5.5. Most threads you read about water treatments and predicted mash pH's are assuming a relatively low liquor-to-grain ratio. Why is this important? The ions in water acts as buffers (they resist changes in pH). As you increase the amount of water (i.e., a high l:g ratio as is commonly found in BIAB) the buffering capacity also increases. This means that BIABers should have a more difficult time getting their mash pH down to the "acceptable" level. A way to combat this is to reduce the residual alkalinity of your water (for an excellent description of res. alkalinity read this and this.) But what is the appropriate RA that we should aim for using BIAB? That was the goal of my experiment.
When surfing the internet, I'm sure you've also read that darker kilned malts provide added acidity. They act on the pH to pull it lower than that of a base malt only mash. So how can we predict what the mash pH will be for a particular grist? Unfortunately it is an extremely complicated system and any predictions are just that, predictions. But we can start to get a general idea of what is happening as we change our water profile.
In my case, I varied the residual alkalinity of my water by diluting it with distilled water. Distilled water has (ideally zero) almost zero ions and is as close to pure water as we can buy as ordinary people. This means that it has zero buffering capacity and diluting another water sample will correspondingly reduce the RA (i.e., a 1:1 dilution with distilled water will result in 50% reduction in RA). It serves as a perfect source to reduce the RA of our tap water, if in fact we need to do any water adjustments.
So here's what I did. I wanted to look at the mash pH of different grists. Obviously the number of grists compositions is virually infinite, but I thought I would attack this from the SRM side of things. If you take the average SRM value of all styles of beer, you'll come up with a value of 14.96 SRM (at least I did). We'll assume this to be one data point. The other two data points I looked at were very low (~5SRM) and quite high (~30 SRM). Now, some well-respected brewing water people DO NOT advocate beer color as an appropriate indicator of resulting mash pH. However, this serves as a convenient method to test a wide range of grists compositions.
I used 3 different grists (100% base malt (1.8 Lovibond), 90% BM + 10% Crystal 120 L, and 90% bm + 10 Roasted Barley (300 Lovibond)). This represents the range of colors listed above, roughly. I also used four different water compositions, thereby spanning a range of RAs from ~130 (quite high) to zero (very low) by diluting my tap water with different amounts of distilled water. (If you want more info on my water profile and dilution factors just PM me). This gave me 12 different samples to work with. Here's a picture:
I created 3 each of 4 different dilutions of tap water with distilled water and brought them to striker temp in side my oven. I then added grain of different compositions, listed above, mashed in and put back in the oven to maintain a normal mash temp. The front row are the samples containing roasted barley, the middle containing C120, and the last row is base malt only. After ~30min I pulled the samples out and measured the pH with a calibrated pH meter.
Here are the results, My water company only gives a range of values for the alkalinity, calcium, and magnesium content. So the solid line is the calculated RA based on the median value of all of these. The dotted lines above and below the solid line represents what the maximum and minimum value should be at any given time.
What does the data show? Well, based on fact that color is such a weak indicator of mash pH, not a whole lot. I think though, it allows us to see that we should be paying some attention to our water profiles when doing lighter colored beers. Surprisingly, the water should be considered for darker beers, as my results show that an acceptable mash pH is only achieved for RA of ~75. If you have soft water that's great news. You can easily get your mash pH into the appropriate range. If you have very alkaline water, then you should consider diluting with distilled water to achieve RA of <50.
Some more details...For all samples I used 100 mL of water (the water was weighed on a scale since I don't have any volumetric flasks, 1mL = 1g) and the total grain weight was 15 g. This gives a l:g ratio of 6.6 kg/L which I think is pretty reasonable, obviously this will change depending the many factors (desired OG, boil time, evap. rate, etc.).
Note, the attached PDF below is the same as the above, just without the axis labels. I don't know how to remove it.
pH of Full Volume BIAB as a Function of Res. Alkalinity
Post #1 made 12 years ago
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Last edited by BrickBrewHaus on 11 Mar 2012, 16:44, edited 4 times in total.
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