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Measuring pH

 

Tools for measuring pH

 

Introduction

pH is a scale used to specify how acidic or basic (alkaline) a water-based solution is. Acidic solutions have a lower pH, while basic (alkaline) solutions have a higher pH. At room temperature, pure water is neither acidic nor basic and has a pH of 7.

The pH scale

Producing the best quality beer possible requires us to measure (and sometimes alter) pH throughout the brewing process. This includes:

  • Mashing: Proper mash pH is required for efficient starch to sugar conversion and to create the intended flavour profile. A higher pH (more basic) produces a sweeter beer due to a less fermentable wort and more body. A lower pH (more acidic) produces a drier beer with thinner body due to a more fermentable wort.
  • Sparging: We lower the sparge water pH to avoid extracting excess tannins from the grain husks. While all beer will have some tannins, with most beers we want to try and minimize the amount. Tannins have a tongue-drying astringent taste like over steeped tea or strong red wine.
  • Boiling: Proper boil pH helps produce a good protein break which in turn helps with beer clarity and long term stability. When lowered, boil pH also minimizes colour formation (important if the goal is to maintain a lighter coloured beer) and helps ensure a less harsh hop bitterness (even though hop utilization is actually increased at higher pH).
  • Fermentation / Packaging: Lower pH is better for long term stability and results in a livelier beer.

Below are two meters with different form factors that we recommend for measuring pH for brewing. Both feature 0.01 pH resolution (0.1 resolution is not fine enough for brewing in our opinion), 2-point calibration for greater accuracy, a temperature probe, a pH probe that is replaceable (they wear out over time), and automatic temperature compensation (ATC)*.

*A note about pH meter temperature compensation as it's a greatly misunderstood topic: pH changes with temperature so the pH values we target will always depend on the temperature of the sample. For this reason, throughout our instructions whenever we mention a target pH we always indicate whether this is for a sample measured at mash temperature (approximately 145-165F) or measured at room temperature (approximately 60-80F). At mash temperature pH is approximately 0.2 lower than at room temperature.

Don't confuse the inclusion of automatic temperature compensation (ATC) in a pH meter to mean that the pH target will always be the same regardless of temperature, as that would be incorrect. ATC only compensates for the change in the electrical response of the pH meter probe with temperature. It does not compensate for the chemical/energy change in the water that naturally makes a hotter solution more acidic (lower pH).

Most publications we've come across fail to provide this extra temperature information when discussing pH, making pH a very confusing subject. Without temperature, comparing pH values with other brewers becomes a futile exercise. It would seem that you should be able to assume that, for example, whenever a mash pH value is given that it always means that the pH was measured at mash temperature but unfortunately that is not the case. Historically a brewery would send a sample of their wort to their in-house laboratory for a pH measurement and the sample will have cooled off by the time the reading was taken. It is only more recently that breweries have started to use inline testing at warmer mash temperatures which results in a lower pH target.

Mash pH at 5.21 after adding mash salts and a bit of 88% lactic acidMash pH at 5.21 after adding mash salts and a bit of 88% lactic acid. Perfect!

Measuring the wort pH and specific gravity in the Boil KettleMeasuring the wort pH and specific gravity in the Boil Kettle

 

Shop control panel kits and parts

 

Parts and tools

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Hanna Phep 5 pH meter, model HI 98128

Hanna Phep 5 pH meter, model HI 98128

The Hanna Phep 5 pH meter (model HI 98128) is completely waterproof and even floats. (Yes, we have dropped ours at least once in our boil kettle!). Just like the digital probe thermometer, if your pH meter is handheld, ensuring it is waterproof is (in our opinion) an absolute must. We don't have to worry about humidity from kettles getting into the unit and cleaning it under the faucet is dead simple and worry-free as there is no chance of getting the wrong parts wet.

The Phep 5 model reads to 0.01 pH resolution (+/- 0.05 pH accuracy), includes 2-point calibration for greater accuracy, a built in thermometer, and automatic temperature compensation up to 140F. If the sample temperature is higher, consider cooling the sample for increased accuracy.

The electrode (tip) is replaceable. When brewing approximately once or twice a month we've been able to get 8-9 years out of an electrode. Once the readings start to jump around, it's time to replace it. See Hanna Phep 5 pH meter replacement electrode (part number HI 73127).

Be careful when purchasing as there is a very similar looking Hanna Phep 4 pH meter (model HI 98127) that only reads to 0.1 pH resolution. Make sure to check the model number.

 

Milwaukee MW102 pH meter

Milwaukee MW102 pH meter

Don't need something quite as portable or want to be able to take temperature measurements separately? Consider the Milwaukee MW102. It's been receiving rave reviews from brewers. The separate pH and temperature probes allow you to take a temperature reading before submersing the (typically more fragile) pH probe.

The Milwaukee model reads to 0.01 pH resolution (+/- 0.02 pH accuracy), includes 2-point calibration for greater accuracy, a built in thermometer, and automatic temperature compensation up to 122F. If the sample temperature is higher, consider cooling the sample for greatest accuracy. The temperature probe can read slightly higher temperatures, up to 158F.

The electrode (tip) is replaceable. Once the readings start to jump around, it's time to replace it. See Milwaukee SE220 replacement electrode.

While the Milwaukee is considered bench-top, it's still small enough to be handheld.

 

Calibration / Storage

4.00 pH solution, 7.00 pH solution, storage solution, laboratory wash bottle4.01 pH calibration solution, 7.01 pH calibration solution, pH meter storage solution, laboratory wash bottle

Calibrating and maintaining a pH meter requires a few extra items:

  • 4.00/4.01 pH calibration solution: Used for doing the lower end of the 2-point calibration of the pH meter.
  • 7.00/7.01 pH calibration solution: Used for doing the higher end of the 2-point calibration of the pH meter.
  • Distilled or reverse osmosis (RO) water: Used to wash off the pH meter electrode before putting the meter into the storage solution until the next brew day.
  • Laboratory wash bottle: We use a plastic squeeze wash bottle to dispense the distilled or RO water to clean off the pH meter before storage. The ones with the curved neck used in laboratories work well.
  • pH meter storage solution: When we're not using the pH meter, we put this storage solution in the cap to keep the electrode from deteriorating. Water (even distilled water) should not be used for storage.

To calibrate your pH meter follow the included instructions. How often you calibrate is completely up to you. Some instructions will say to do it once a month, or every time you use it if high accuracy is required. We do it about every 6 months which is about every 6 batches.

To limit the amount of calibration solution required, we use a 1mL (1 cc) syringe (without needle) to fill tiny containers or beakers. Make sure to use distilled or RO water to rinse off the pH meter probe and shake dry between calibration steps. Never touch the ball tip of the pH probe or attempt to dry it with a cloth or any other method that involves touching the probe. A good hard shake (like is done with an old fashioned mercury thermometer) is all that is needed.

After calibration, discard the calibration solution that was used. You cannot re-use it. Make sure to rinse the meter well before using to wash off all storage or calibration solution. Rinsing with regular tap water is fine if you intend to use the meter immediately. 

There's no need to store the pH meter in pH meter storage solution in between measurements on brew day. After reading, simply rinse off the meter with distilled or RO water and shake dry. At the end of the brew day, rinse it again, fill the probe cap with storage solution and close. You may see some white crystals form on the outside after a day or two. This is normal and is storage solution that has seeped out a bit and dried. It can be left until the next brew day. If you don't plan on using the pH meter for a few months, check it periodically and add more storage solution as required.

 

What about pH test strips?

ColorpHast pH Strips (4.0 - 7.0 range)ColorpHast pH Strips (4.0 - 7.0 range)

Little pH test strips are available that test in the important 4-7 pH range. So why not use pH test strips instead of a pH meter? There are many reasons:

  • We test our pH quite often from the start to end of the brewing process from grain to bottle (often as many as 20 times when it's a new recipe) so pH test strips actually cost more in the long run. Most home brewers that use pH strips only use them to measure mash pH, and while that's likely the most crucial point during the beer making process for an accurate pH level, it's not the only one.
  • Strips are not temperature compensated so all samples must first be cooled to room temperature before use. This greatly slows down the brewing process. Our recommended pH meters are temperature compensated.
  • pH strips are very slow to return a result. You have to wait until the colour stops changing which can take up to 10 minutes! A pH meter only takes seconds.
  • And most importantly: Strips are not as accurate. The colour gradients appear so similar that in practice you'll be lucky if you can even get to +/- 0.6 pH accuracy. Take a look at the picture above. It's the color coding to which you have to try and match what you see on the strip of paper. The colours look almost identical in the arguably most important 5.0 to 5.5 range making it too hard to tell exactly what your pH actually is. Our recommended pH meters measure to a resolution of 0.01 pH and gives you the result in numbers, not ambiguous colours.

Every brewer we know that bought a box of pH test strips still has most of them left as they have simply stopped using them.

Proper control of pH is a critical step to brewing any style of all-grain beer consistently and successfully. This simply cannot be done without an accurate method of measuring pH. We recommend a pH meter be used instead of test strips.