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Kaiser · 06-29-2009, 06:54 PM

I need your help.

I think that EMD’s colorpHast strips are the best value for home brewing pH measurement unless you really want to take very precise control over your pH. But even if you have a pH meter you should have these strips as a back-up. They are maintenance free, require no calibration and batteries. They are also fairly easy to read with a +/- 0.15 pH precision. At least I think so.

But a while back I ran an experiment that compared colorpHast strips against a pH meter and I found that the colorpHast strips that I have were off by about 0.3 pH units across a wide pH range. Recently other brewers sent me some of their strips and I noticed a similar error. I now have the hunch that colorpHast strips are always off by 0.3 pH units (i.e. they match color that corresponds to a pH 0.3 units lower than the actual pH. For example you read 5.3 on the strip but the meter reads 5.55). I’d like to confirm that to issue a general guideline that you should correct the reading of the strips by +0.3 pH (or whatever the mean turns out to be).

So I’d like to test this on as many of these strips as I can. Here is my plan:

- If you are interested in participating post here and I’ll PM you my address. (For privacy reasons I may not give my address to members who joined after this has been posted)
- Place 2-3 strips in an envelope addressed to me. They have to be of the 4-7 pH kind as sown below

these are the strips that I have

- I’ll then assign each group of strips a number and note the number on your envelope (having a return address or a note with name would be helpful)
- Then I prepare 2 small mashes. One with a pH of ~5.3 and the other one with a pH ~5.8 and dip all the strips in these mashes for the same time
- the mashes will also be tested with a calibrated pH meter.
- finally I take them all out, wipe off residual wort and take a picture of all the strips in day light along with the color scale I have for my strips
- I’ll do the same with a sample of beer (pH ~4.1-4.5)
- The result will be published and I will let each participant know the number of their strips.

To me that sounds like a very valuable experiment and the participation cost is the cost of 3 strips and a stamp.

So, who is in?
This invitation is going to be posted on the NB forum as well to broaden the base. And don’t worry, this is not a scam

Kai

mrkristofo · 06-29-2009, 07:03 PM

You're sure that the pH meter isn't off?

I have a meter in the lab that I can calibrate on a curve to 8 points, and could use to verify the strips are indeed defective.

If you're meter's spot on, and this problem turns out to be pervasive you ought to let the manufacturer know. Many chemists will be happy to know.

Kaiser · 06-29-2009, 07:15 PM

Quote:

Originally Posted by mrkristofo

You're sure that the pH meter isn't off?

I have a meter in the lab that I can calibrate on a curve to 8 points, and could use to verify the strips are indeed defective.

I'm sure the pH meter is not off. I actually have a new one and I can make a simple test tonight if the strips are still 0.3 units off.

If you can test the strips independent from my experiments, please go ahead and do so. Make sure you test them with wort though, just in case that it has something to do with wort.

Once I have enough data points I may also contact the manufacturer.

Kai

desertbronze · 06-29-2009, 07:21 PM

I'm in - PM sent. Thanks for doing this.

**GilaMinumBeer** · 06-29-2009, 07:24 PM

I dunno Kaiser.

Looking at the EMD Chemical site it appears that all the ColorPhast test strips have a inherent pH unit sensitivity of 0.5 as listed. So, I think if you called the chemists they'd respond "Great, the strips are working as intended".

Just a thought.

Kaiser · 06-29-2009, 07:46 PM

You are probably right about the manufactuerers response. They will be careful about what they say and take the safe route of saying that the strips meet specification and that we expect too much from them. You would need to get to someone who cares (maybe a fellow home brewer) and can give a non BS answer about what can be expected from the strips. I know Jamil has been pushing these strips as well and claimed that they are spot on with his pH meter. When I told him that mine are off by 0.3 he didn’t believe me and hinted that I must be doing something wrong when reading them.

I’m interested in getting a large sample size from all over the place and once I have photos everyone can see for themselves. If the error is all over the place we can make a statement that these strips aren’t as precise as everybody thinks they are and that you are best off aiming for a pH of 5.5 which would allow your actual mash pH to be in the range of 5.2 – 5.8. The latter assumes a hypothetical random error of +/- 0.3

Kai

Edcculus · 06-29-2009, 08:25 PM

I don't own any strips, but I think this is a great idea. If you can prove they aren't accurate within .3, then I won't even waste my $ unless I get an actual pH meter.

What you are basically saying though is that if they are off by that much, they are pretty much useless if we are trying to target a specific mash pH? If I wanted to target 5.2, then with these strips my mash could be anywhere between 4.9-5.5?

Kaiser · 06-30-2009, 01:37 PM

I finally got around to sending the PMs. I hope I didn’t miss anyone.

Some more points that were brought up:

- I’ll be making small sample mashes of 50 ml water and 12.5 g malt. I have practice with that and I’m willing to spend the time and malt
- You may send info on when the strips were bought but we can also gather that once I have the results.
- placing the strips in a plastic bag could help keeping moisture away. Especially since it has been raining almost non-stop here in NE for the last weeks. I can’t guarantee that my mailbox is perfectly dry.
- If you have a pH meter yourself you can also conduct a similar experiment. The more data the better. But I’d still like you to send me a few strips. When you do the experiment please take a picture of the strip next to the color chart. This removes the ambiguity of interpreting the color. Last night I did a test run with the strips I have and should be able to post the pics tonight. This way you can see what I mean.

Thanks,
Kai

Kaiser · 07-01-2009, 02:15 AM

Here are the pictures I took last night:

For this picture the wort tested at a pH of 5.53. And I would match the strip to 5.3 because it still has more of a yellow tint to it

For this the wort tested at 5.78 and I would match it to the 5.5 color.

Hence the inclination that my strips are off my 0.3

Kai

Kaiser · 07-16-2009, 02:47 AM

The "data" from the colorpHast experiment is in!

What I did:

I solicited colorpHast strips from members of the NB forum and the HBT forum. Only folks from the NB forum actually sent strips. But I still feel that I should post the date here as well:

I then prepared 2 mini mashes by heating 50 ml distilled water to ~60 C (140F) and added 12.5 g pulverized grist. This is a mash thickness of 4:1 (~ 2 qt/lb). After 10 min I cooled these mashes to 25C in an ice bath and tested the pH with a calibrated pH meter. The precision of the pH meter is +/- 0.02. I also took a sample of beer and heated it to 25C for testing.

I then inserted all the strips into this mash, held them in there for about 30s, removed them and blotted the excess liquid before I lined them up on a piece of white pater. On that paper I also placed the color scale. After that I took a picture of that in tungsten light. The pictures were taken in a RAW format and I later color corrected them and adjusted their brightness such that the background in all the pictures has the same color. I made sure that no color adjustments like hue and saturation were active. The final step was using Gimp to assemble pictures that show the strips and the color scale. Those pics are posted below.

What I now like you to do is to look at the pictures and try to match each of the strips to the color scale. Note that there is no number 6. You may use numbers between the numbers shown on the color scale to express cases where the strips may match an intermediate color. I'd also like to to give your match a confidence interval in which you feel. E.g:

mash A:
1: pH = 5.0 +/- 0.2

Once enough have gone through this exercise I'll collect the data and also reveal the actual pH values measured for the samples.

blank pH strip color:

mash - A:

mash - B:

beer:

Let me know if you have more questions about the procedure.

Kai