The big colorpHast experiment

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

http://braukaiser.com/wiki/images/f/f4/Colorphast.jpg

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

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.

mrkristofo said:

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.

Click to expand...

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

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

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.

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

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?

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

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

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

Mash A
1. 5.0
2. 4.9 +/-.1
3. 5.0
4. 5.0
5. 5.0
7. 4.9 +/-.1
8. 5.0
9. 5.0
I am fairly sure on these except 2 and 7, which are a touch lighter.

Mash B
1. 5.4 +/- .1
2. 5.2 +/- .2
3. 5.2 +/- .1
4. 5.4
5. 5.3
7. 5.1 +/-.1
8. 5.4
9. 5.1 +/-.1

This one was tougher. Many of those defiantly could be the +/-.1 or 2.

Beer
1. >4.0
2. 4.0 or less than 4.
3. 4.2 +/-.2
4. 4.2 +/-.2
5. 4.4 +/-.3
7. 4.4 +/-.3
8. >4.0
9. 4.0 +/-.2

Something you might consider is color matching software. I think the gimp will do this or has a plug-in that will. That way you just know.

Anything for Kaiser
BTW, I would have sent you some but I just found this thread today.

If they are .3 off, they are utterly useless as a 5.7 mash and a 5.4 mash are very different. I did a mash at 6.0 once(er well that's what it came to) and had horrible efficiency.

I’ll try to present all the date in an elegant way in a graph. I still have to figure out what would make most sense.

Now that we all had a shot coming up with our own readings of the strips I can reveal the pH meter numbers:

mash A : pH = 5.35 +/- 0.02

mash B : pH = 5.66 +/- 0.02

beer: pH = 4.40 +/- 0.02

In general all strips read about the same pH within ~0.15 pH units. This seems acceptable for mashing. But there is also a systematic error of ~0.3 for the mash pH measurements. This is what I expected based on the experience with my strips. Now I can say that this error can be assumed for all colorpHast strips. I don’t know if this is specific to testing wort.

Kai

Just saw this for the first time.

I noticed that 1,4 and 8 strips were ever so slightly darker right out of the box.
2 and 9 are slightly lighter.
And in most of those pH tests the strips also followed that trend...but there were exceptions (esp with the beer).

I use pH strips but those are not the ones I use or I def would have participated (had I seen the thread that is). I use the ones that go from 4.6-6.2, which are probably even less accurate even though the range is smaller. They're very cheap.

Maybe pH strip manufacturer lot# (if there is one) should be tracked as well for this study. It might correlate to the slight color differences observed.

When John Palmer talked about mashing and ph he indicated that you need to cool the wort, although I guess it wouldn't matter much because the strips and the meter were both done at mash temps.

Let me start by saying that I am a lowly extract brewer, so I am not that familiar with how sensitive the efficiency is to the pH. However, as a chemist by trade, I would never trust a paper strip from any manufacturer to get me closer than 0.3-0.5 pH units.

Also, if you do want to bring this data to the company like you mentioned, I would suggest getting a couple of friends to repeat your experiment. It will hold a lot more weight if several people observe the exact same phenomenon.

Here is a chart for mash A:

seems like you're right... 3 to 3.5 low.

Nablis said:

When John Palmer talked about mashing and ph he indicated that you need to cool the wort, although I guess it wouldn't matter much because the strips and the meter were both done at mash temps.

Click to expand...

Yeah 5.2 is only ideal at mash temp. I believe he says 5.4 is the ideal mash pH around 70F.

z987k said:

Yeah 5.2 is only ideal at mash temp. I believe he says 5.4 is the ideal mash pH around 70F.

Click to expand...

Yeah I would be interested if the strips are also off at room temp.

Nablis said:

When John Palmer talked about mashing and ph he indicated that you need to cool the wort, although I guess it wouldn't matter much because the strips and the meter were both done at mash temps.

Click to expand...

I missed this the first time around.

It matters bc a meter shows a different pH at mash temp (about 0.2 lower) while the strips have the same color reaction at mash and room temp.

Kai

Kaiser said:

...a meter shows a different pH at mash temp (about 0.2 lower) while the strips have the same color reaction at mash and room temp.

Click to expand...

Great thread Kai. Yesterday I did a mash and measured the pH just below 5.0 at 149F with some 4.6-6.2 strips. It looks like I should have cooled the wort to take the measurement. Assuming the strips are accurate (which I doubt because they're even cheaper than the colorpHast strips), what does this mean?

jescholler said:

Yesterday I did a mash and measured the pH just below 5.0 at 149F with some 4.6-6.2 strips. It looks like I should have cooled the wort to take the measurement.

Click to expand...

I've used the same strips and the temperature doesn't seem to matter much as I always got the same color at 100F as I did at 150F.

But, yes, you're correct - the Precision Labs 4.6 - 6.2 strips are very inaccurate. The strips consistently measured a pH below 5 even with 5.2 buffer in the mash. My solution, throw out the strips and rely on 5.2 buffer.

Or, you could continue using the 4.6 - 6.2 strips and stop acid/salt additions once the strip changes from orange to yellow (reads < 5). Of course, this will vary slightly from mash to mash, but the strips will certainly get you in the ballpark.

Or, you could continue using the 4.6 - 6.2 strips and stop acid/salt additions once the strip changes from orange to yellow (reads < 5). Of course, this will vary slightly from mash to mash, but the strips will certainly get you in the ballpark.

Click to expand...

This is pretty much all I do with those 4.6-6.2 strips. Except I'm just trying to get 'no red'. If it's light orange I figure I'm in the ballpark...I don't think I've ever had it go all the way to yellow. But maybe this is wrong because I never seem to need as much salt additions as Palmer's Spreadsheet says. Just adjusting to get to one end of the 'range' is usually enough to get a pH in the low 5s.