pH and Water Activity Explained for Home Curers

Last updated November 2, 2026.

Two numbers do a lot of the safety work in a dry salami. One is pH, which is how acidic the meat gets. The other is water activity, written aw, which is how much of its water is still free for bacteria to use. Neither one is cooking. That's why they matter so much.

BCCDC sums up how a salami stays safe without heat: fermentation, curing agents and drying together result "in acidic pH and low water activity that provides process control for product safety" (BCCDC 3.13).

What pH is

pH is a scale for acidity. Manitoba's food-safety guide puts it simply: "pH is a measurement of acidity or alkalinity in a food using a numerical scale from 1 to 14. A pH below 7 is acidic, a pH of 7 is neutral, and a pH value above 7 is basic or alkaline" (Manitoba pH Meter Guide). Lower means more acidic.

Fresh meat isn't very acidic. BCCDC says the pH "of fresh meat is approximately 5.6-5.8" (BCCDC 3.13). Fermentation is how you push it down. The starter culture makes lactic acid, and the pH drops. We cover that step in detail in Fermenting salami.

Fresh meat and fermentation on the pH scale. Illustration, not a photo: pH runs from 1 to 14, and below 7 is acidic. Fresh meat is about 5.6 to 5.8, and fermentation pushes it down. AMI says fermented sausages "shall attain a pH of 5.3 or lower" within the degree-hour limit. Not a schedule; it shows no timing.

What water activity is

Water activity isn't the same as how wet something is. FSIS defines it this way: "Water activity, abbreviated as aw, is a measure of the concentration of moisture (i.e., water) and its availability in a food." It adds that "if ingredients such as salt or sugar are added to food, they compete with the bacteria for available water" (FSIS-GD-2023-0002). New Zealand's MPI calls it "a measure of the water in the food which is available for bacterial growth" (MPI UCFM guidance).

So salt and drying both lower aw. Salt ties water up, and drying takes it out. Lower aw means less water for bacteria.

Why the two work together as hurdles

No single step carries the load. FSIS calls these products "multi-hurdle" and says "Generally, one step is not sufficient on its own to eliminate pathogens of concern, instead a combination of processing steps or hurdles is needed" (FSIS-GD-2023-0002).

Here's one example of how they team up. FSIS says that in dried meats "the acidity (reduced pH) and dryness (reduced water activity) of dried meats create conditions that prevent germination" of Clostridia spores (FSIS-GD-2023-0002).

And here's why aw alone isn't enough. AMI notes that S. aureus "can grow in foods with low water activity, i.e., 0.86 under aerobic conditions or 0.90 under anaerobic conditions" (AMI Foundation GMP, via UW-Madison). That's why the pH has to drop fast first, before drying has done its part.

Typical targets, and who sets them

You'll see slightly different numbers depending on whose guidance you read. They aren't interchangeable, so note which one you're following.

pH during fermentation. AMI says fermented sausages "shall attain a pH of 5.3 or lower" within the degree-hour limit (AMI Foundation GMP, via UW-Madison). The degree-hour math lives in Fermenting salami.

BCCDC's shelf-stable combinations. For room-temperature storage, BCCDC's Table 5 says the product must contain a "minimum of 100 ppm nitrites/nitrates AND" a "minimum of 2.5% salt AND" meet one of these: "the aw of the finished product is 0.85 or less, regardless of pH, OR," "the pH of the finished product is of 4.6 or less, regardless of aw OR," or "the pH is 5.3 at the end of the fermentation period and the end product has an aw of 0.90 or lower" (BCCDC 3.13). The salt and cure amounts are what our cure calculator is for.

Dry vs. semi-dry. BCCDC says "the final aw is what defines if a sausage is semi-dry (aw >0.90) or dry (aw ≤0.90)" (BCCDC 3.13). Semi-dry sausages, it says, have an aw "higher than 0.9, therefore these sausages require refrigeration."

New Zealand's figure. MPI says "It is generally accepted that UCFM products with a combination of pH<5.2 and aw<0.95 are shelf stable (Meat & Livestock Australia, 2015)." It also says "If it takes longer than 48 hours for the pH to drop below 5.2, or if the pH does not drop far enough, then there is a likelihood that pathogenic bacteria or toxins will still be present" (MPI UCFM guidance). That's written for licensed NZ producers who validate their process. The copy we opened is the 15 November 2017 version, saved in a web archive. MPI lists this guidance as last updated 11 September 2025.

FSIS's figure. FSIS says salt-cured products are dried to a water activity "sufficient to achieve shelf-stability by preventing the growth of microorganisms (e.g., water activity ≤ 0.85)" (FSIS-GD-2023-0002).

Our call: at home, we'd aim for the BCCDC combination of pH 5.3 by the end of fermentation and aw 0.90 or lower, along with BCCDC's salt and cure minimums. That aw is stricter than MPI's 0.95 but looser than the 0.85 that FSIS and BCCDC's aw-only option use. To be clear, that's our choice, not a rule any of these agencies wrote for home curers. Hitting it doesn't prove the salami is safe, and it isn't a reason to store homemade salami at room temperature.

How to measure pH at home

Calibrate first, every time. Manitoba says "A pH meter must be calibrated against a known standard to assure accuracy each time it is used." For acidic foods it says to "calibrate with a neutral buffer (pH 7.00) and an acidic buffer (pH 4.00)." Temperature matters too: "the pH meter must be calibrated at the same temperature as the samples being tested" (Manitoba pH Meter Guide). It also recommends "a pH meter with an accuracy of at least ±0.02 units."

The slurry method. Michigan State University Extension's quick guide says to "Blend 10 g of sample and 90 mL of deionized water," then put the probe in and stir "until the pH reading is complete" (MSU Extension quick guide). MPI's standard method is a little different: "Mince a representative portion of the sample of the UCFM product and place that portion in a stoppered bottle with twice its weight of water. Shake at 5 minute intervals for 30 minutes and determine the pH value of the liquid electrometrically at 20°C" (MPI UCFM guidance). Pick one method and use it every batch.

Spear probes and strips. MPI allows "calibrated, direct-contact pH probes or spear electrodes," but says probing must be "done aseptically so that microorganisms are not introduced into the product." Skip the paper strips. MPI says "Indicator strips have generally proved to be unsuitable for measuring the pH of fermenting products," because "The fat in the product may coat the indicator pad" (MPI UCFM guidance).

Write down every reading with the time. AMI says "pH readings must be taken from each lot" (AMI Foundation GMP, via UW-Madison).

How to measure water activity

Water activity takes its own meter. MSU's guide says to "Calibrate/verify water activity meter with 0.250 and 0.760 standardized NaCl solutions," then prepare the sample "by finely dicing enough sample to cover the bottom of the sample cup" (MSU Extension quick guide). If you don't own one, a lab can test a sample for you.

Why weight loss is only a proxy

Most home curers track weight, and it's a useful guide. BCCDC's worked example says "generally a 30% weight loss is desirable" (BCCDC 3.13). Our drying guide walks through tracking it.

But weight isn't aw. MPI says "Weight loss may be used as a proxy for aw of UCFM product if properly correlated," and that the link is set "by having the aw of a selection of product samples that have achieved the intended weight loss analysed by a laboratory." It only holds "Provided that the formulation and processing parameters don’t change" (MPI UCFM guidance). Change the recipe or casing, and the old correlation is gone.

BCCDC's same example ends with a caution: "Product could be shelf stable if a water activity meter was used and the end-product meets the parameters for shelf stability" (BCCDC 3.13). In other words, weight loss on its own doesn't get you there.

There's another trap. A dry outer layer can hide a wet center, which is case hardening. A salami like that can hit its target weight and still be underdried inside.

Our call: keep homemade salami refrigerated. If you haven't measured aw, weight loss alone tells you even less.

What the numbers do and don't guarantee

This part's serious. Hitting your targets is necessary. It isn't proof the salami is safe.

FSIS answers this head on. Asked whether meeting degree-hours and drying to a low aw is enough, it says: "No. Fermentation and drying alone are not particularly effective as lethality treatments." It adds that "Degree-hours are intended to control the outgrowth of S. aureus. To reduce levels of other pathogens, such as Salmonella, STEC, and Lm, products often need to be fermented to a lower pH than 5.3." And size matters: "smaller diameter products tend to dry faster than large diameter products, and the shorter drying time is often not enough time to achieve the same reductions in bacteria as larger diameter products even if it is enough time to achieve the targeted water activity" (FSIS-GD-2023-0002).

BCCDC says the same thing more bluntly: "With fermented sausages that are ready-to-eat with no cooking step there can be no guarantee that all pathogens have been destroyed" (BCCDC 3.13).

So what do good numbers tell you? They tell you that you met the conditions these agencies use to control growth. That's worth a lot. It still isn't a lab test.

If the pH hasn't reached 5.3 by the degree-hour limit, throw the batch out.

When in doubt, throw it out.

Sources

Read our disclaimer. This page is general education, not professional food-safety advice.