Salifert vs Murphy

[Dave S]

I am quite confused now! My recent Murphy's report indicated an alkalinity of 165. This was in contrast with my previous Salifert test of 195.

Sooo, I decided to do another Salifert test today. First I used the included standard check solution of 2.4 meq/l. Result: 2.39. Next using my tap water. Result: 3.99 (199.5 ppm).

So what's going on? I'm inclined to believe Salifert, in which case can I believe the other results from Murphy's. I have to say that the other mineral levels did tally with my local water report.

Anyone care to comment?

[oz11]

Alkalinity can, and does, vary from day to day. I don't see anything to be concerned about with those results. All this means is that you should test your liquor each and every time you brew.

Hope this helps

[Dave S]

Alkalinity can, and does, vary from day to day. I don't see anything to be concerned about with those results. All this means is that you should test your liquor each and every time you brew.

Hope this helps

I don't believe it's varied that much in a couple of days. All Salifert tests done in the last 9 months have all indicated somewhere in the mid to high 190's range. The only reason I haven't done one in the last month or two is because the scale had rubbed off the syringe at the 1 ml mark, introducing a chunk of guess work. I've got a new syringe now so can resume.

Thing is I don't fancy paying another £18 for a second opinion. Might write to Paul Taylor to see if he can shed any light.

[vacant]

But what does your beer taste like?

[Dave S]

But what does your beer taste like?

That's a good point. The last 2 brews - one porter, on IPA taste excellent, and that's based on an alkalinity of 195. So I think I'll probably stick with the Salifert results.

[gnutz2]

Imo, you wont be able to taste any difference that 30ppm of alkalinity would make.

[Dave S]

Imo, you wont be able to taste any difference that 30ppm of alkalinity would make.

Maybe not. I'm still inclined to trust the Salifert result though I think, based on the calibration test result.

[Wezzel]

I am intending to send a sample to Murphy's this week for testing. I think I will do a Salifert test on the sample before I send it just to see how close the two reading are.

[Belter]

Paul writes on here as far as I'm aware. Crookedeyedboy. I've emailed him far too many times with queries on my report. Most of the time he says that you won't notice the difference in such a small change. I'd be more inclined to believe a mass spectrometer than a salifert test kit.

[WallyBrew]

I'd be more inclined to believe a mass spectrometer than a salifert test kit.

So would I if it's set up correctly but I suspect that it will be crap at measuring total alkalinity

[Eric]

I'd bet on Murphy's figures being more accurate than what can be obtained with a home aquarium test kit. Their test is probably worth every penny, getting more than just a figure for alkalinity and it should lead to confidence in your own testing and help confirm your findings. However, it's not this, but the next stage where lies a common problem for homebrewers and I would suggest not using acid to reduce alkalinity unless you can measure the result.
My water's alkalinity is typically 240 mg/l CaCO3, but when making a delicate pale beer, this would be brought down to maybe 15. It wouldn't take a big error in the acid added to substantially miss that figure. I don't bother with an initial test, but, in the case given with CRS (AMS), add 24ml to 20 litres of water from which will come my mash liquor. It can take quite some time before the reaction is complete as the acid can sink to the bottom with all remaining bicarbonate above it. Only then is the first reading taken, which I will frequently do in reverse (I know, I know) by putting a measured amount of reagent in the test tube and then add the water with a calibrated syringe.
Final adjustment is made to suit with more acid or water, if overdosed, and the final alkalinty is recorded. From the volumes of acid and water used, salt contents can be calculated and the initial alkalinity recorded. I will frequently do a GH test at this time that I might know the total calcium and estimate total salt contents.

[gnutz2]

Wow, I test the water, treat it, then brew!

Although, on my last brew I did do a test after adding the crs which was supposed to bring alkalinity down to 20, It read about 8.

[Kev888]

Theres a post somewhere that discusses how murphy's and some other forms of total alkalinity measurement can differ - IIRC it was something more than (just) variation between test batches; I seem to remember graham had something to say on the matter as well as crookedeyeboy but sadly I can't recall the details. Will have a look around in case I can find it.

EDIT: here it is - theres a bit of discussion and crookedeyeboy posts an explanation from their quality manager lower down the page

EDIT2: I should also say that my own salifert kit results and subsequent adjustments have always worked pretty well at getting the mash PH correct brew after brew after brew, and it seems to for many others as well. Obviously it can be done wrongly, but if you've used the kits regularly you'll probably know if you personally have had a track record of correct results or not, as well as how much your water varies brew to brew. I wouldn't expect two results to be 'precisely' the same, but in my case if there were any 'great' dissagreement from any other source then I'd struggle to overlook what (for me) has been a very well proven test on the actual brew water being used at the time.

Cheers
Kev

[fisherman]

I use a Salifert test kit ,altough I would like a Murphy's test now and again.
I don't use syringes for measuring liquids anymore. I use my scales for my mineral addition . The scales only weigh up to 100 grams but seem great.
How accurate are we with tiny syringes?.
Happy Brewing