Bicarbonate and Efficiency- How Big a Deal?

My water report is in..

Bicarbonate = 266
Sodium = 16
Potassium = 2
Ca = 96
Mg = 25
Tot Hardness = 344
Sulfate = 11
Cl = 56
Carbonate = <1
Tot Alk = 218
pH = 7.7

The thing that stands out, as I almost exclusively brew pale ales is the bicarbonate.. I want it around 35. I know it's going to hurt my mash eff; but how much if I leave it as-is? 2% or 20% or what, compared to a bicarbonate level of 35?

If I do pre-boil my water to precipitate the bicarbonate.. Should I siphon the water off the precipitate or just use it after the boil including the precipitate? Other ideas on reducing the bicarbonates, other than diluting with distilled or RO water?

Thanks for helping with this!

It's not so much a question of efficiency as it is of the overall quality of the beer. For the best beers the mash pH must be in the proper range and that is hard to achieve when the alkalinity is high.

Precipitation of bicarbonate with calcium by boiling is the most common means of decarbonation used by home brewers. Treatment with lime is another. With either about the best you can expect to do is to reduce alkalinity to about 50 (bicarbonate around 60). In either case the clear water is decanted off the precipitate. The remainder of the bicarbonate can be converted to CO2 gas with an acid which would be needed anyway in most beers to move the malts to the proper pH. Most home brewers in the US will use lactic or phosphoric acid for this though the relatively low levels of sulfate and chloride in this water make sulfuric or hydrochloric or a blend feasible choices and that is what most brewers in the UK would use.

Thanks ajdelange for the reply and thoughts.

I stumbled upon Palmer's Mash RA spreadsheet today and the section in his book and the spreadsheet has been very informative... I see the easiest solution to my problem is a 50% dilution with distilled water and addition of a small amount of Epsom salt for me to arrive at acceptable levels for a pale ale. I remain curious though... aside from spending another $30 for a water test of the post boiled and decanted water, is there a way to accurately know the bicarbonate ppm after boiling and decanting? Also, are other mineral levels seriously affected by boiling and removing from the precipitate?

TIA!

A 50% dilution cuts everything in half (approximately) so that your alkalinity after a 1:1 dilution will be about 109. With boiling it should go to about 50 but no, there is no way to know for sure what happens without testing. I always try to convince people to buy hardness and alkalinity test kits and check for themselves. They are relatively inexpensive.

The only other ion that boiling is going to effect is magnesium. Calcium will be removed preferentially as calcium carbonate is less soluble than magnesium carbonate and you have more than enough calcium to remove all the alkalinity. Nevertheless, a bit of magnesium may well precipitate.

I would not add epsom salts. You already have plenty of magnesium and more is generally flavor negative. If you want more sulfate get it from gypsum.

For pale ale I'd recommend a 9:1 dilution. This will get your alkalinity down to 22. This is low enough that with a calcium addition back up to 50 mg/L you can probably get away without adding acid. See the Primer. Or you could boil and assume that you drop alkalinity to 50, then dilute 1:1 and follow the Primer. If you get good precipitation then it's probably a safe bet that you got the alkalinity down to that level.