Acidifying sparge water in HLT

[Yooper]

I have read that acids should be added to cool water, and then the water heated. But what about when the HLT is already heated with water to use in the mash?

I heat all of the water that can fit in my HLT, generally a tad less than 14 gallons. I put 9 gallons into my MLT, so I have 5 gallons of sparge water and need to add two gallons of tap water to that for my total. (I wish I had a bigger HLT!). Anyway, I need then to acidify this sparge water, but the water is 150 degrees at that point.

Can I add my phosphoric acid at that point, with the same results I would have had at adding it at 65 degrees? What is the reason to add it cool, and then heat the water?

Sorry if this is a silly question. I'm just trying to wrap my head around how to go about doing this.

 

[IslandLizard]

You can add your brewing acid whenever you're ready for it, whether the water is hot or cold.

The general direction of adding acid to cold water is meant for diluting strong or concentrated acids to prevent splashing and sudden boils. In your case you're adding only a few ml of (90%) phosphoric acid to a tank full of water. No problem.

 

[mblanks2]

I add my acid to already heated sparge water as well. I use 85% phosphoric, so very small additions but I've never had any issues.

 

[dstar26t]

From a Bru'n Water Facebook post:

"WHY CAN'T I ADD MY ACID TO HEATED WATER?

Bru'n Water users may have noted that the program tells them to add their acid to the water before its heated. Here is the reason why you should heed that recommendation or revise your process.

When we have an accurate tap water report, the amount of acid calculated for the acidification dose is based on the alkalinity from that report. When you heat water, you start reducing that alkalinity. Adding the acid dose that was calculated based on the original alkalinity means that you will end up overdosing the acid.

However, it is OK to add acid to hot water, but you will need to determine what the alkalinity of that heated water is in order to properly calculate the acid dose. If you prefer adding acid to your hot water, it's recommended that you obtain a water report for that heated water so that the reduced alkalinity is used in your acidification calculation.

It's not the temperature, it's the change in alkalinity that produced the original recommendation!"

 

[mblanks2]

From a Bru'n Water Facebook post:

"WHY CAN'T I ADD MY ACID TO HEATED WATER?

Bru'n Water users may have noted that the program tells them to add their acid to the water before its heated. Here is the reason why you should heed that recommendation or revise your process.

When we have an accurate tap water report, the amount of acid calculated for the acidification dose is based on the alkalinity from that report. When you heat water, you start reducing that alkalinity. Adding the acid dose that was calculated based on the original alkalinity means that you will end up overdosing the acid.

However, it is OK to add acid to hot water, but you will need to determine what the alkalinity of that heated water is in order to properly calculate the acid dose. If you prefer adding acid to your hot water, it's recommended that you obtain a water report for that heated water so that the reduced alkalinity is used in your acidification calculation.

It's not the temperature, it's the change in alkalinity that produced the original recommendation!"

Now that makes sense.

 

[ajdelange]

Does it? Let's suppose we have water at pH 7 with alkalinity (to 4.3) of 101.6 and calcium hardness of 100. This is balanced. The 1.6 is the alkalinity of the water itself. Now we heat it and half the calcium (1 mE/L ~ 20 mg/L) coalesces with 1 mEq/L carbonate (30 mg/L) from 1 mEq/L bicarbonate to form 50 mg/L CaCO3 which lies on the bottom of the vessel. What is left above it is water saturated WRT CaCO3 at pH 8.32 and its alkalinity is 52.2 ppm as CaCO3. But the alkalinity of the 50 mg/L CaCO3, still on the bottom of the pot, to end point 4.3, is 49.8 so the alkalinity of the contents of the pot is 99.8, not very different (0.8 ppm as CaCO3, about 1%) from that of the original water.

Now is that enough to make a difference? Let's suppose that we wanted to adjust the pH of this water to 5.5 using phosphoric acid. It would take 169.8 mg/L phosphoric acid to acomplish that. Now suppose we add that much acid to the water we have heated. The pH would end up at 5.6. I'll leave it to the reader to decide whether he thinks that is significant or not but I do want to point out that the pH of the mix is very sensitive to small changes in acid or alkalinity levels because we are, at mash about 1 pH away from the first pK of carbonic acid, 6.38. In other words we are on the flat part of the titration curve where a small amount of charge change implies a large pH shift (relative to near the pK).

Another thing to consider here is volume changes with heating. That can amount to several percent so be sure that volumes are calculated relative to cold water. Small errors is acid measurement are clearly a factor here which could easily induce a change of 0.1 pH. But we also need to ask what is the effect of being off by 0.1 in our water pH on mash pH. The answer is very small for the same reason: we are on the part of the titration curve where the acidified water has minimal buffering capacity, that is, the part where almost all the bicarbonate (main alkalinity source) has been removed.

Bottom Line: Add acid to either hot or cold water* but stir thoroughly not only to disperse the acid but to be sure that any CaCO3 that has precipitated is redissolved. If you don't see any turbidity then don't worry and if you do then stir until the water is clear again. Check with a pH meter.

Now if the water turns turbid when heated this is a gift. Heat it till it boils, then let the chalk settle and rack off the clear water. Replace the lost calcium, if desired. In most cases the water will have been decarbonated to about 1 mEq/L (50 ppm) and you won't need acid. If you do the amount is about 1 mEq/L - less than you would have needed if you relied on acid alone. It is always a good idea to check the alkalinity and hardness of water you have decarbonated by boiling or lime treatment.

*This assumes that you are adding a dilute solution. Do not add concentrated sulfuric acid to hot water as the reaction is very exothermic.

 

[Yooper]

I'm scared- I'm actually starting to understand most of what AJ says.

AJ, seriously, thank you for that detailed reply.

here's my scenario- I have an HLT that holds a titch more than 14 gallons. Generally, it's all RO water, or nearly so, depending on what I'm making.

Today, my mash water is 9 gallons. That will leave me 5 gallons in the HLT. My HLT is constantly stirred with an automatic stirrer, so there is a slight vortex. I need to add 2 gallons of tap water to reach my sparge volume. That will make the temperature of all the water in the HLT 155 degrees, as the tap water will be out of the faucet and the HLT water (the RO water) will be 175. The alkalinity of the 7 gallons total will be right about 70. I need to add very little phosphoric acid to it- like 6 ml if my memory is correct (data sheet is home and I'm currently at our cabin).

I've done this numerous times, and all with good results, but it could be that since the majority of the water is RO water that my small acid addition isn't really needed. In the last batch, I had a lot more tap water and used about 20 ml of phosphoric acid in the sparge water. Then I read that I shouldn't heat the water and then add the acid, and I wondered why that would be.

I should note that while I have a high bicarb level in my tap water, I've never had any scaling or precipitate in that HLT since acidifying my sparge water, or sparging with 100% RO water. In smaller batches, that use less than 14 gallons of water total, I generally do sparge with 100% RO water.

 

[ajdelange]

I'm scared- I'm actually starting to understand most of what AJ says.

Delighted!

The alkalinity of the 7 gallons total will be right about 70. I need to add very little phosphoric acid to it- like 6 ml if my memory is correct (data sheet is home and I'm currently at our cabin).

That's pretty close to the limit to which you can decarbonate by boiling (50) so it would be unlikely that any CaCO3 would precipitate and if any did it would be tiny, tint crystals which would redissolve pretty quickly when acid is added.

...but it could be that since the majority of the water is RO water that my small acid addition isn't really needed.

Quite possible. In a 90% base 10% caramel (60L) mash with the base malt DI pH being 6.2 and water of 70 ppm alkalinity assuming equal calcium hardness you might expect a mash pH of about 5.53. The bicarb in the water will suck up about 31 mEq of protons and the base malt 33. The caramel would provide 54.5 at this pH and the calcium 10.5. Were you to use enough phosphoric (about 31 mmol) to neutralize the water's demand the pH might drop to 5.46. Note that I am not claiming to be able to predict pH to two decimal places. I am only displaying them so that you can see the magnitude of the probable shift: -0.07 pH.