ColorpHast pH Strip Information

I received this interesting information from a friend of mine who spoke with a technical services representative from EMD, the producers of the ColorpHast plastic pH strips.

The Rep said that to use ColorpHast strips correctly, the strip immersion time must be from 1-10 minutes until no further change is noticed. He said that this is because of the very low ionic concentrations of what brewers measure, (ie: water/mash/wort/beer). He went on to say that the quick "Dip and Read" will NOT render a correct pH measurement. He also confirmed that the strips do read about 0.2 - 0.3 units low at mash temp. So the findings of Kai Troester and AJ Delange about the readings of these strips are confirmed.

Another thing the EMD Rep mentioned, was that ColorpHast strips have an expiration date of 3-5 years IF they are stored in a closed container with a desiccant (moisture-removing agent). Apparently the strips are adversely affected by air moisture. If the strips are not carefully stored and protected, they have a typical shelf life of 1-2 years.

Enjoy!

The findings are really Kai's and not mine. I'm color blind and so not much good when it comes to evaluating test strips. I did help Kai with one of his experiments but he sent me photographs of strips and I measured their color using the color meter in my computer.

Not sure I buy the ionic strength argument. Wort has fairly decent ionic strength from all the minerals in the water and the minerals in the malt.

If you check the instructions for use of most pH strips they do say to leave in the liquid until the color stops changing but this is usually for a few seconds - never heard minutes cited before. Also not sure I buy the temperature argument because the strip cools to room temperature quickly once it is withdrawn. But I would certainly say that if a man tells you how to properly use his product you should listen to him.

mabrungard said:

...
The Rep said that to use ColorpHast strips correctly, the strip immersion time must be from 1-10 minutes until no further change is noticed. He said that this is because of the very low ionic concentrations of what brewers measure, (ie: water/mash/wort/beer). He went on to say that the quick "Dip and Read" will NOT render a correct pH measurement...

Click to expand...

That's already well known, since the package itself says to immerse for 1-10 minutes, until no further change.

mabrungard said:

... He also confirmed that the strips do read about 0.2 - 0.3 units low at mash temp. So the findings of Kai Troester and AJ Delange about the readings of these strips are confirmed...

Click to expand...

I'm not so sure that confirms Kai's findings. Kai concluded that they read 0.3 low at ROOM temp. He commented that they tend to read the same at room versus mash temp, and that his pH meter will read 0.2 low at mash temps. So I have to wonder if this rep was a little confused about the mash temp thing -- he likely thinks they read like pH meters, correct at room temp but both will read low at mash temp. I would tend to ignore his comment unless he acknowledged that (a) they also read low at ROOM temp, or (b) they read the same at room and mash temp.
Kai's thread:
https://www.homebrewtalk.com/f11/big-colorphast-experiment-126033

mabrungard said:

...Another thing the EMD Rep mentioned, was that ColorpHast strips have an expiration date of 3-5 years IF they are stored in a closed container with a desiccant (moisture-removing agent). Apparently the strips are adversely affected by air moisture. If the strips are not carefully stored and protected, they have a typical shelf life of 1-2 years.

Enjoy!

Click to expand...

Yikes, guess I need to buy new strips!

Since this has come up I thought it might be a good idea to give some details of the method I used to come up with pH estimates for Kai's experiment. In a nutshell I did what Kai did but used the color measurement software in my computer to interpret the color rather than depend on my color blind retina to do it. Here's a procedure:

1. Dip the strips in a cooled sample of the mash liquid and keep them in it until color development is complete.
2. Shake off or blot away the excess liquid.
3. Place the strip adjacent to the legend on the strip packaging and take a photograph. Let the camera use its internal white balance scheme. It is relative color we are after - not absolute. Make sure the exposure spans the camera's dynamic range. Check with the histogram feature if the camera has one.
4. Transfer the image to your computer. Use the computer's color analysis software* to measure the L*a*b* color of the legend patches closest between which the color of the sample patch lies. Use a large aperture to average over as many pixels (all within the patch, of course) as you can.
5. Estimate the pH of the sample from

pH = blo + (blo - bsamp)*(pHhi - pHlo)/(blo - bhi)

For example, one of the test strips for the A wort in the post referenced in #3 read a b value of bsamp = 33.8. The closest legend color patches were the one for pHlo = 5.0 which read blo = 36.5 and pHhi = 5.3 which read bhi = 24.5. Thus the pH estimate is

pH = 5.0 + (36.5 - 33.8)*(5.3 - 5)/(36.5 - 24.5) = 5.0675

The meter determined pH for this wort was 5.35 and the average pH over the 8 images in the photo was 5.04 with a standard deviation of 0.03. For this single case the strips show a tight clustering with the now widely published bias of 0.31 (call it 0.3 - easier to remember).

*The Mac used to come with a digital color meter that was quite versatile but they dumbed it down in the latest OS release. However, some enterprising fellow put the Classic Color Meter at the Ap store for $2.99. It has all the features they took out. As Microsoft tends to eventually mimic everything Apple pioneers I assume something similar is available for the PC world.

I chose to use b* from Lab space for my analysis. You could, of course, use L*, R, G, B, x, y, u, v or whatever color parameter you choose. I chose b* because it exhibits greater change with respect to pH than a* and I didn't try L* because I was looking for color differences which brings us to an interesting point as depicted in the attached graphic. This shows a* vs b* for the legend and for the 8 test strips from the A wort in Kai's experiment. Note that the colors of the test strips do not lie along the curve suggested by the legend. Thus the brewer is tasked with trying to compare colors which do not match the legend to the legend. Not wonder it is difficult. This is, I believe, a major contributor to the problem.

Two things:

1. I compared old to new colorpHast strips on brew day yesterday. I found that 5 year old strips (stored in just a plastic bag) read 0.1 higher than the new strip I bought this week. I just took two data points so YMMV.

2. AJ - you may want to reconsider analyzing a* and b* if the strip colors don't fit well. I analyzed the strip colors with Irfanview on my PC and using Luminosity, Red, & Green seemed very consistent (Blue did not work well). Here are sample results when I calculate the "implied pH" separately for L, R, G:

--Sample---L----R----G---
Sample#1 4.75, 4.75, 4.77 (average=4.75)- mash @15min, new strips
Sample#2 4.87, 4.84, 4.93 (average=4.88)- mash @15min, old strips
Sample#3 4.84, 4.82, 4.88 (average=4.85)- mash @45min, new strips
Sample#4 4.92, 4.88, 4.96 (average=4.92)- mash @45min, old strips
Sample#5 4.75, 4.84, 4.93 (average=4.88)- mash drained, batch sparge added
Sample#6 4.81, 4.81, 4.82 (average=4.81)- pre-boil pH


From this, I conclude that I could probably simply analyze either L or R or G, but analyzing each channel and taking an average seemed pretty reliable.

SpeedYellow said:

2. AJ - you may want to reconsider analyzing a* and b* if the strip colors don't fit well.

Click to expand...

Please understand that I am not advocating using L*a*b* or any other color space. You should use, for analysis, the color parameter that shows the greatest sensitivity to pH. In Lab space that is b* (or perhaps L* which I didn't try). The graph clearly shows that b* is much more sensitive to pH (the axes are not scaled equally) than a* and it is even possible to read the pH from the b* axis quite accurately with a range of 5.0 - 5.1 (average 5.04). Not so for a*. It is plainly not sensitive to pH and indicates an average of about 4.8 with a range 4.7 - 5 . I think when I did the analysis for Kai I tried R, G and B and found R to be the most sensitive.

I tend naturally to look first to Lab as it is independent of device and white point and, best of all, color differences measured in it are at least approximately independent of where you are in the space (what colors you are measuring the differences between). I wanted to see of the sample test strip patches were consistent with the legend. Lab is really the only space in which simple color difference measurement is possible. The only way to measure color differences in R,G,B space is to convert them to Lab. Thus Lab was chosen so I could see how much the colors differ from the legend. This doesn't make a* a better or worse choice than R for pH estimation using this technique.

Now at the same time as the a* axis is expanded relative to the b* axis the statement that the colors do not fall on the curve implied by the legend needs to be taken with a grain of salt. Then are off the curve by perhaps 3 units of a*. Three units of color difference in Lab space is considered a fairly good match. But they are also off the curve by about 5 units of b* for a rough DeltaE of sqrt(2^2 + 5^2) which is about 5.4. Not such a good match but not a terrible one either.

Nuisance post from a water science newb:
Doesn't the color of the wort stain the strips? I had hell reading them recently. I didn't trust that I was blotting it off correctly and was worried about missing the real pH. Doesn't help that the near-desired pH color was very close to my mash liquid color.

I've always thought that might be the case. How else would you explain the fact that the colors of tests don't match the colors of the legend? But I'm told the newer plastic based strips don't actually absorb any wort and thus don't stain. But what about the chemical patch?

Hey Guys,

I just wanted to post my research results regarding the German made ColorPhast pH Test Strips; purchased from the link in the water primer sticky.

With a test group of dark wort (Homebrew), light wort (Homebrew), finished beer (Home brew), finished beer (commercial), mash liquid (Nano brewery) and water (Tap, RO, and spring) I have come to the following results…empirical, quantifiable results.

ALL (Yeah, I know right?!?) test samples proved to react with the test strips EXACTLY THE SAME, in the exact same time frame even though the tests were conducted under varying temps, conditions, etc.

I purchased the broad range (0.0 to 14.0) and a narrow range (4.0 to 7.0) to test the group. Both ranges reacted the SAME way. Both strips were “dipped” and held in varying temps from 154 down to 37 degrees for 10 seconds. The color development on all samples and all types in all conditions was roughly two minutes.

Granted, I have a fairly keen eye for color so that “may” have played into it…IDK

My overall opinion: I love ‘em! Simple, effective, and accurate in varying conditions. And, for what we are doing as home brewers… an easy application that works well. The conditions that we [home brewers] will employ these strips in are way simpler than that of my research and test conditions. The plastic strips do not absorb liquid and the strips cool / warm / equilibrate almost immediately once placed in an ambient environment. No, I am not affiliated with any company or research group and I have NEVER used these strips before. I was after an alternative to the pH meters that was low maintenance, idiot “resistant,” and fairly inexpensive. The pH test strips deliver. I actually ordered the strips BEFORE I read all the info on actual meters so I was worried I just wasted $35 (after shipping). Not the case. These strips are useful and give me what I need….Easy, quick, accurate [enough for my applications] data used to make on the fly corrections.

I’ll post this in the primer as well….

Cheers,

-JM

How did he readings compare to your pH meter readings? Did you perform any measurements with a pH meter? Just curious, not trying to give you the third degree.

Precision is not important to me if there is no accuracy. Just FYI, the accuracy of strips has been shown to be quite suspect, as you will no doubt hear shortly.