Summer 1998 Vol. 1 No.2
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pH Meters: what to look forMore than 90 percent of the scheduled processes approved by the Food Venture Center (FVC) require the processor to check the pH of the product before it is bottled or shipped. Since the pH is often the determining factor whether or not the product will be safe to consume, it is very important that testing be done correctly and accurately. At this point, we are going to assume you know what pH means and how the scale works. By law, if product pH is less than 4.0, it can be checked with simple pH papers (often called litmus strips). This method is inexpensive, but it has drawbacks. Firstly, if the product tested is thick or highly colored, the color of the strip may not be easy to determine. Secondly, if the product pH is normally close to 4.0say 3.8 or 3.9you may not be able to detect a formula deviation that sends the product above its safe pH level. Thus, it is our position that a wise manufacturer invests in a good pH meter! Here are the most frequently asked questions about pH meters. 1. Where can I get a pH meter? The best place to purchase a meter is through a scientific supply company such as Empire State Scientific Co., Inc., Hanna Instruments, Krackeler Scientific, Inc., Cole-Parmer Instrument Co., or Whatman LabSales; VWR. (See more information at end of article). 2. How much do they cost? pH meters can be purchased for under $100 to over $1000. We do not normally recommend the cheapest ones nor do we advocate the most expensive ones, either. I have been able to find good quality meters with desirable features for under $300. Keep in mind that the better quality meters generally last longer and take relatively more abuse. 3. What should I look for in a pH meter? Accuracy should be the first consideration. The very best (very expensive!) meters have an accuracy of ±0.002 pH units. These instruments are meant for research and are overkill in the food industry. Most food processors should look for a unit with an accuracy of ±0.01-0.02 pH units. If you are making flavored vinegars that have a very low pH where it is highly unlikely they will approach anywhere near the 4.0 range, you can "get away" with one of the less expensive models that typically has an accuracy of ±0.2 pH units. That means, the instrument could be reading 0.2 units above or below (±) the actual pH of the product. If the normal product pH is 3.2, and a batch happens to deviate to 3.4, a meter reading of 3.6 or 0.2 units above the actual pH is not going to matter too much. However, if the product usually has a pH of 4.0 (the scheduled process says you must stay at 4.2 or below) and the product deviates to 4.1 but your pH meter gives you an actual reading of 4.3 because you bought a cheapie, then you are going to either add more acid to the product and change the flavor (and your profit margin), or loose the entire batch of product because you do no thave any acidulant on hand! A more accurate meter would have detected whether or not the product was still within the specified range and whether it was okay. Now just imagine what could happen if your pH meter reads 0.2 units lower that it should be and your product deviates to above 4.4. In that instance, you could wind up with a very dangerous product on the market and you will not know it until someone gets sick! Here are some other features to consider: Calibration. All pH meters can be calibrated (checked against a known standard) to assure accuracy. Most meters can be calibrated to at least two standards at the same time. Calibration Standards or Buffers: You should order at least two bufferspH 7 and pH 4. The pH4 is necessary because your meter should be calibrated to a standard that is no more than 3.0 pH units from your product. Sometimes buffers are sold in sets of 4, 7 and 10. The pH10 buffer is generally not needed in the food industry. Just be sure that you do get the pH4 and pH7 buffers! Electrodes: This is the part of the instrument that is immersed in the product. Once again, your product determines what you need depending on whether or not it contains oil. Oil does not have a pH value and does not affect the other ingredients in the product, but it can easily clog the electrode and cause erroneous readings. Very oily products (such as salad dressings) that are emulsified well enough so the oil is not easy to separate, require the use of a "sure-flo" electrode. These are a little more expensive, but will last longer and give better results than the standard type of electrode used in adverse conditions. For products with small amounts of oil, or products that can be tested before the oil is added (or if it can be separated out), standard electrodes supplied with most meters work just fine. When pricing meters, make sure that you know if the model you are considering comes with the electrode or if it will have to be purchased seaparately. That great deal you thought you had might not be such a deal after all if you have to buy an electrode separately! Temperature: pH readings are affected by temperature. The best way around this is to buy a meter that has automatic temperature compensation. Of course, this costs a little more, but you wind up with an instrument that can also give the temperature of a product if you are hot-filling at a specific minimum temperature. If you choose a non-temperature compensated pH meter, you can either cool the sample to room temperature before taking a reading, or use a temperature compensation chart to determine the correct pH of your sample. A word of cautionif you choose a temperature compensated instrument, be sure that its range includes the fill temperature of your cooked product. Shop carefully! Talk to sales representatives and ask lots of questions! You want and need an accurate, easy-to-use instrument, but there is no need to pay several hundred dollars to get a better one than you need. The FVC does not endorse any particular company or instrument, but check out Hanna Instruments, specifically HI 8424, for what seems to be a good value.
Read: Chemical Food Preservatives
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