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The importance of accurate pH in salami testing

Salami pH is one of the “safety hurdles” that needs to be achieved when making a fermented sausage. Regardless of the type of salami you plan on making your pH must be below 5.3. This is considered the safe zone.

Recently we were making some very unusual salami (nothing new there). After stuffing the mince meat into our casings we began the process of fermentation. For these salami (Buffalo Wild Wings and The Worlds Hottest Salami) I was using the starter culture “Flavor of Italy“. I love this culture as it produces exceptional and consistent salami. My fermentation conditions were normal. 75F and 90% humidity.

After about 7 hours of fermenting I tested the pH with my Hanna pH meter as I had done countless times before. Upon testing, the reading I got was 5.0. PERFECT!! Time to start drying.

This starter culture is known for a rapid pH drop. Usually it takes 18-24 hours but today for whatever reason it hit it’s target in 7 hours. I didn’t think much about it and so I placed the salami into the drying chamber.

This was my first mistake. Starter cultures generally act the same, especially if your recipe is fairly consistent. The 7 hour pH drop (according to my pH meter) should have been my first indication that there was a problem. Temperature plays a vital role in fermenting your salami. The higher the temperature that you ferment at the faster your pH will drop. Being that my fermenting temperature was on the low side this should not have happened.

It wasn’t until I reached my target weight loss that I figured out what the problem was and by that time it was too late. The salami was ruined (but a great lesson had been learned).

After 2 months of drying and my target weight loss had been achieved I realized that my salami was incredibly soft. It felt as if it was raw inside. My initial thoughts were “case hardening” but the outside felt soft as well. It wasn’t till I tested the pH inside (with a new pH meter) that I discovered what the issue was.

Every pH probe (regardless of the manufacturer) has an expiration date. Depending on how it’s used and maintained a pH probe could last between 10-18 months. The lesson I learned was that if you use your pH meter past it’s expiration date you will start to get very inaccurate readings. In my case specifically my pH meter gave me a reading of 5.0pH but in reality the pH of my salami was probably closer to 5.5pH. A pH of 5.5 is “Danger Zone” territory where bad and unwanted bacteria can live and thrive.

Every pH meter has something called a “slope value”. The slope value is a calculation that your ph meter makes to convert the millivolts (mV) of your samples in to a pH reading. The slope value is represented by a percentage and the acceptable tolerance for this percentage is usually between 105% and 85%.

This means that if your pH meter has a slope value of less than 85% it has reached it’s expiration date and your reading will no longer be accurate. So how do you know what the slope value is for you pH meter?

That’s where Apera Instruments comes in. Apera Instruments sell a specific pH meter (Apera PH60S-Z) that comes with an app and can be operated through your smart phone. What really caught my attention about this meter and it’s Bluetooth capability was that on the home screen of the app there is a slope value that’s automatically calculated for you. Problem solved!! Now I know without guessing and with 100% confidence that my pH probe is good and giving me accurate readings.

In addition to knowing the slope value this particular pH meter through the app delivers more features and benefits that I’ve ever seen in a pH meter. Things like data logging, real time tracking, GPS locator, the ability to share your information, alarm settings, and much more. This pH meter has far exceeded my expectations and is well worth the money.

How to figure out the slope value

So what do you do if you already have a pH meter and you want to figure out the slope value? Here’s what you need to do.

There are 2 ways to find out your slope percentage. The first way requires that you know the millivolt readings of your calibration solutions. If you have a pH meter that shows you that data then you can figure out the slope value. It’s generally shown as “mV” on your meter. Here’s what you need to do.

Calibrate your unit in 7.0 solution then 4.0 solution. Make sure that your solutions are at 77F (25C). Temperature does make a difference. When you calibrate your meter in the 7.0 solution record the millivolts that it reads. Then calibrate your meter in the 4.0 solution and record the millivolts for that. Subtract the 7.0 mV from the 4.0mV and divide that answer by 177.48. Then multiply your answer by 100 to get the slope value percentage. If it’s between 105% and 85% you are good to go!! Here’s an example:

ph7= +15mV
pH4= +175mV
0.9015×100= 90.15%

In this example your slope value percentage is 90.15%

The second way is if you don’t have the millivolt readings on your device. Here’s how to find your slope percentage using this method.

Place your probe in your pH7 solution (lets say it is 6.96) and record that number. Next place your probe in you pH 4 solution (lets say it is 4.03) and record that number. Subtract those 2 numbers and divide the answer by 3 (which is 7.00-4.00). Here’s what it should look like:


Regardless of the method that you pick your samples must be at room temp (77F) and they must be fresh.

Knowing your salami’s pH is important but knowing that your pH meter is giving you accurate readings is of the upmost importance. Next time you pull your pH meter out be sure to apply the formula and calculate the slope value. Enjoy the video and let me know if you have any questions..

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27 thoughts on “The importance of accurate pH in salami testing”

    1. Hello Elmar. Generally when making salami the salumist will take a small amount of mince meat (usually from the stuffing horn) and set it out to ferment alongside the salami in a casing. When it comes time to test for pH the small sample of mince (that’s not in a casing) will be tested. This way you don’t have to puncture a whole in your casing to test the pH. If you watch any of my salami making videos you’ll see what I’m talking about. You can check out this post and if you watch the video fast forward to the 10:30 mark.

      So to answer your question. The only way to test the meat is to either open an end up or poke a pH meter into it.. I can tell you though if you used TSPX, added .2% – .5% dextrose to your recipe, and let it ferment at room temperature for 48 – 72 hours then there’s a decent chance your salami hit it’s target. It should feel firm, be brighter red/pink, and have a beautiful fermented smell.. But testing the pH is the only way to know for sure (especially if you don’t know what you’re looking for) I hope that helps. If oyu have any other questions please be sure to let me know..

  1. Hi Eric, I just found out your website and really like it. I have two questions:
    1) Can you ferment salami with no culture?
    2) Can you test the PH with PH strips?
    Thanks in advance.

    1. Hi. You can ferment without a starter culture but the results are very unpredictable and your success rate may be low. You can test the pH with strips. Just be sure that the strips measure in the tenths place. 4.5 – 5.5 (or something like that) You are looking for a ph of anything under 5.2.

  2. Hey! love the channel, Did my first try on salami two days ago. Ph read at 18 horus vas 5.8, 40 hours later it went up!!! 6,11!!!!!

    What are posible reasons for this other than my ph meter is NOT properly calibrated? Any ideas?

  3. Hi Eric,
    I was making a salami and left it for fermentation for 24 hours. I checked the ph after 18 hours and it was 5.6. I let it go for another 6 hours to finish the 24 hour fermentation.
    i made an error and didn’t check the final ph in haste, and assumed it would be ok, I hanged the salami in dry curing chamberafterwords.
    it kept bugging me all night, and today i came and checked the ph and found it to be 5.6.
    So i pull the salami out of the dry curing chamber and put it out for fermenting for another 24-48 hours.
    Now, i will check the ph before i put them back, but the question is, “is the culture gonna make it back?” i hope it didn’t die within 24 hours in the curing chamber.
    any advise.

    1. It should be fine. Raise the temperature during this final fermentation and check it at 6-12 hours. What starter culture did you use and at what temp did you ferment?

      1. The name of the cultre is “safe pro F-LC”.
        The temp of the chamber where the salami is fermenting is 32*c( it’s a hot day today). I covered it with cling wrap, poured water on tray.
        Just like i did before.

        1. Strange. FLC works very fast at those temps. How much dextrose did you add? Also what’s the expiration date on the culture? Out of curiosity. What’s the PH now?

  4. Hi Eric, do I test for PH only once? Do I need to keep the sample sausage for additional tastings? Can I cook it to check the flavor? Or do I just toss it after the first test?
    Thank you

    1. Hey Wally, Once you reach your ph target you don’t need to test again. At that point you can discard the sample or coat it in some polenta corn meal and place it in your chamber to dry with everything else. Once it’s really firm it’s ready😁

  5. Hi Eric, I am confused, are you saying you should budget $250.00 every 10 to 18 months for a PH Meter? Or is the probe a component of the meter and is replaceable at a lower cost? I am just a hobbyist any suggestion for a low cost way to measure PH, if the whole meter has to be replaced?

    1. I am saying that every pH meter on the market will eventually fail. Depending on the use and how it’s maintained it could last 12-24 months. Mine generally last around 2 years.. The Apera unit allows you to only replace the probe which is around $100 bucks..

  6. Hi Eric,
    I just did my PH level reading after 41hrs and it measured 5.3.
    Should I wait to get under or is it safe to proceed and place into the cooler?

  7. I did a batch of salami in my Stagionello cabinet and the ph dropped to 5.2 in about 48 hours. Then I set the cabinet to 60 degrees and 70% humidity and the ph rose to 5.8. Any idea why? Is it safe to continue?

  8. Hi,
    Using Flavor of Italy and the Apera you recommend. Hit 5.2 in 14 hours at 81%. Wanted 4.96. Waited a total of 30 hours. Still 5.2. My very first salami. Why did the ph quit falling? Just put it in my seasonal curing cabinet. Hope it’s going to be OK. At least it’s not over 5.3. Must have done something wrong.

    1. Fermenting isn’t an exact science. Sometimes it gets finicky depending on the recipe that you use, the amount of fat in the recipe, where you test the salami, the amount of moisture in the meat, and the spices that are used. When fermenting you can always leave the meat out a little longer of necessary. If you are fermenting at 75f you can fo 48 hours without any issues. If you are fermenting at 65f you can leave it out for 72 hours. The sugar is also very important. If you find that you are consistently getting stuck at the 5.2 mark, you can always increase the amount of sugar by just a little bit to give the bacteria more food. Out of curiosity, How much salami did you make and did you weight the starter culture or did you use tsps to measure it?

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