How much citric acid to reach 3.5 pH?

[Brushwood Brewing]

Given that I used to have "Chemist" in my job title (many years ago!), I'm embarrassed to ask, but:

I'm going to try making hop water for the first time. For food safety, I want to add citric acid to get the pH to around 3.5. I will be starting with my own unfiltered well water.

How much citric acid (in grams or teaspoons) should I add per 1 gallon of water to reach 3.5 pH?

(I know that the starting pH of well water varies, and will affect how much acid to add. I'm just looking for a ballpark amount to get started, and then will adjust as necessary from there using pH strips.)

Thank you in advance.

 

[lumpher]

About 1/4 tsp/gallon of water will drop it by 1 point.

 

[AlexKay]

The short answer is that it depends on your water (and specifically on carbonate species concentrations), so much so that even a ballpark guess is hard to make.

I'd start at 0.1 g/gallon, and adjust by doubling (or if you're in a hurry, quintupling) the concentration repeatedly.

A slightly wacky idea that occurs to me is to get both citric acid and sodium citrate (dihydrate), and dump lots (>>1 g) of each in, in a 2.5:1 ratio. That'll do the trick for pH. You'll taste it, but for hop water that might not be a bad thing.

 

[Brushwood Brewing]

Thanks. Looks like I'll have to pick up a smaller scale that can measure fractions of a gram. I'll give it a shot this weekend.

 

[cactusgarrett]

As mentioned, a bunch of variables mean "it depends". Here's what I just used to make a gallon test batch, if it can help give you a basis of comparison:

1 gal RO water + 0.5 g CaCl2
1.0 g citric acid during the initial boil (before hops) -> pH 3.16
0.2g additional citric acid brought it down to pH 2.98
Performed a dip hop in 2 cups of the boiled water
Mixed and cooled, entire 1 gal batch ph = 3.13

I was targeting pH 2.9 ultimately, and my approach was to err on the low side for taste and food safety purposes. I still missed a touch high, but it tastes great and is well below the pH requirement for food safety.

 

[Brushwood Brewing]

Thanks. Picked up my scale already. It ended up taking 2.6 grams of citric acid to get me to ~3.5. My pH strips only show 0.5 increments, but from what I read, I think that's good enough for food safety.

 

[Brushwood Brewing]

Just an update: When I said I used 2.6g/gal above, that was before I steeped the hops. After steeping the hops, the pH rose significantly and I had to add more citric acid to get the pH back down below 3.5. I've done this twice now and settled on 3.4g/gal to reach a pH of <3.5.