Given the large amount of darkly-roasted grains in a Russian imperial stout, the pH is almost guaranteed to be lower than desirable when the strike water has a low level of bicarbonate ions (<50 ppm). (Strike water is the water used to mash your grist.) If you use any of the standard water chemistry calculators, the amount of carbonate ions they suggest for Russian imperial stouts is quite high. And in practice, you usually don’t need that much bicarbonate to approach proper mash pH. This is because darkly-roasted grains are not more acidic than dark crystal malts — the correlation between color and acidity breaks down when you jump to the darkly-roasted grains. Here is one way to deal with mash pH in a Russian imperial stout. There are certainly others, but I like this approach for a couple reasons (that will be clearer when we discuss lautering).
My approach is to formulate the recipe, then consult my water calculator to see how much baking soda (NaHCO3) I would need to add. Frequently, the amount is fairly high. Then I remove a portion of the dark malts from the recipe such that the total amount of darkly roasted grains is 10% of the grain bill. Next, I redo the water calculations to see how much baking soda I would need to add with the reduced amount of dark grains. This amount will always, obviously, be lower.
When I actually mash, I first mash in a mixture of the base malts and enough darkly-roasted grains that they constitute 10% of the initial grist. I use strike water with the lower amount of baking soda added. After 40 minutes, I take the mash pH and then stir the remaining dark grains into the top of the grain bed, adding more of my previously prepared to strike water to maintain the proper mash thickness. After stirring the remaining dark grains in, if the pH is in the proper range, I don’t make any adjustments to the amount of baking soda. If the pH was low, I would stir in the grains, and add baking soda so that the mash now contained the full amount from the original calculation. (I’ve never had to do this, however.) After 20 more minutes of mashing — for a total of 60 minutes — I would then proceed to recirculate the wort and prepare for wort collection.
The basic idea is to begin the mash with a ratio of base grains to dark grains similar to that of a dry stout. The amount of sodium bicarbonate (baking soda) needed to address the mash pH is reasonable. Once the bulk of starch conversion has occurred, I stir in the remaining dark grains. This is mostly because it is easier to lauter, but it also allows the early part of a mash to work without having to add too many minerals to the strike water. In addition, you may not need the “extra” baking soda suggested in your original calculation. Again, this is because darkly-roasted grains are not proportionally more acidic than crystal malts, something not taken into consideration when beer color is used to calculate the residual alkalinity required to neutralize it.
Sodium Bicarbonate vs. Other Options
Sodium bicarbonate (baking soda) is more effective at neutralizing acid than calcium carbonate (CaCO3, chalk). However, do not add so much baking soda that your sodium concentration exceeds 100 ppm. (If the sodium levels in your water are naturally high, you may have to use calcium hydroxide (slaked lime) instead of baking soda to neutralize acids in your mash. However, calcium hydroxide is corrosive and is best avoided unless absolutely necessary. And even so, you’ll need to review how it can be safely handled.) Finally, in practical terms, there is no reason to ever exceed 250 ppm of bicarbonate, even if your brewing calculator suggests this.
As I mentioned before, this is not the only way to handle the mash. I used this method several years ago when I was formulating and tweaking a super big stout, and it worked well for me. However, I have not tried every possible mashing option, so I can’t say that this is absolutely the best way to do it. All I can say is that it worked very well for me. In researching this article, I did find that Kai Troister’s site has a water calculator that takes the proportion of roasted malts into consideration. I look forward to comparing that to Palmers spreadsheet. Another simple option would be to change all your darkly-roasted grains to dark crystal malts (80–120 °L) for the purposes of your water calculations.
You should not add bicarbonate to your sparge water. In fact, if your water is naturally high in carbonates, it is best to either “cut” the water with distilled water, or bring down the bicarbonate level with acid. Bicarbonate ions help when mashing a dark beer. However, they are not serving any purpose in sparge water. Bicarbonate additions in strike water are meant to raise the mash pH. You should not need additional pH adjustment while you sparge. Sparge water with high level of bicarbonate ions can lead to astringency, something that big beers are already prone to.
In the next installment in the series, I will discuss malt selection, starting with the dark grains.