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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6 thoughts on “The importance of accurate pH in salami testing

  1. Paola marafioti
    Paola marafioti

    Hi Eric
    Thatโ€™s great! I will support you all the way! ๐Ÿ˜Š๐Ÿ˜Š

    1. Eric

      Thank you Paola!! Glad to see you on my blog!! I can’t wait to try the cheese culture/salami experiment!!

  2. Elmar Bagir
    Elmar Bagir

    Hi, how do you test it if meat is already in casing, especially if someone uses UMAI casings? Regards

    1. Eric

      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..

  3. Doru

    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. Eric

      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.

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