Acidity determination plays a critical part in ensuring that consumer products meet requirements for attributes such as appearance, texture, taste and nutritional content.
It guarantees that foods and beverages are produced for consumers with consistent, well-defined properties including shelf-life.
Acidity testing is also vital in ensuring products meet regulatory requirements and do not present safety or health issues for the consumer. In short, acidity is an important attribute of many foods and drinks.
Learn how acidity affects food processing, and how accurate acidity testing helps to ensure product quality in the food and beverage industry, download our guide “An Introduction to Acidity Analysis: Selected Techniques to Monitor pH and Acids”.
Acid may be present in foods and drinks naturally, developed during processes such as fermentation, or added during processing as a standard means of preservation: pH values below 4.6 limit the growth of microorganisms such as Clostridium botulinum, the causative agent of botulism. Therefore, acidity testing is important throughout the entire food processing value chain.
Acidity measurement is the main criteria to indicate freshness and composition of raw ingredients and perishable foods. A quick pH assessment can determine, for example, whether raw oysters have been cleaned well enough to prevent food poisoning, or hint at the presence of mastitis in dairy herds.
Titration furnishes more detailed clues for certain perishable items – including milk, oil and fruit juices – that are sold as blends or may be subject to adulteration. For example, milk with elevated levels of lactic acid may be contaminated with bacteria, while tartaric or malic acid in blended juices points toward the presence of certain types of fruit. In products like fresh juice, this testing can be an important part of meeting local labeling requirements, in addition to preventing allergic reactions or other forms of illness.
As noted, the results of a food or beverage’s acid content determination can indicate how long it will last on shelves, often paired with strict temperature-control requirements. The United States Code of Federal Regulations (CFR), Title 21, Part 114 stipulates that most foods and beverages preserved via acidity must be assessed by an approved method. Potentiometric measurement via pH or titration is suitable for products with a pH between 4.0 and 4.6, with the results related to the final equilibrium pH. By contrast, any method may be used for foods with a pH below 4.0.
There are two interrelated concepts in F&B analysis that involve acidity: pH and titratable acidity. Each has its own impact on food quality.
Titratable acidity measurements deal with the total acid concentration of a food (also called total acidity). pH measures acidity in terms of H+ ions present in the sample (also called active acidity).
pH indicates a food or beverage’s degree of acidity or alkalinity. A pH meter measures this acid strength in terms of the potential difference between a reference electrode (like Calomel or Ag/AgCl) and a pH electrode (glass electrode).
This difference is then related to the concentration of H+ ions in the solution and corresponds to the acidity of the solution.
Foods and drinks display a broad range of pH values, which relate to the sample’s acidity or alkalinity. Some foods such as meat, dairy products, alcohol, lemon juice, carbonated water, and vinegar fall towards the acidic end of the pH spectrum, whereas common vegetables and fruits fall towards the alkaline end, as shown in the following table.
| Item | pH range |
| Ketchup | 2.00 – 2.60 |
| Vinegar | 2.40 – 3.40 |
| Fruit jellies | 3.00 – 3.50 |
| Strawberries | 3.00 – 3.90 |
| Apples | 3.30 – 4.00 |
| Apple juice | 3.35 – 4.00 |
| Fruit jams | 3.50 – 4.50 |
| Pickled cucumbers | 4.20 – 4.60 |
| Tomato puree | 4.30 – 4.47 |
| Tomatoes | 4.30 – 4.90 |
| Cucumber | 5.12 – 5.78 |
| Tofu | 7.20 |
We offer a comprehensive portfolio of sensors for pH measurement, including specialized sensors that are useful when measuring the pH of solid or semi-solid samples. We also offer highly usable and compact portable meters and benchtop meters to pair with your pH sensors.
To learn how this portfolio can assist you with accurate acidity determination in food samples, visit the Sensor Product Guide.
Titratable or total acidity can be determined by titrating the known amount of sample using a titrator along with a sensor or indicator. Depending on the type of titration, the titration endpoint can be determined by sensor or using a color indicator. This technique provides a more accurate acidity testing method for the total acid content of the sample. Acid-base titration, redox titration and colorimetric titration methods are used to determine acid content using titration.
Acid-base titrations utilize pH sensors to quantify the titrant necessary to react with malic, tartaric, citric, acetic and other organic acids present in fruit, juices, vinegar-based condiments and wine, to name a few. It can be determined by titrating the sample with a strong base that neutralizes acid present in the sample.
Generally, redox titrations are performed for ascorbic acid determination in beverages and sulfite content determination in wines. Ascorbic acid is titrated with 2,6-dichlorophenolindophenol (DPI) where it undergoes a redox reaction and exchanges two electrons. The electron exchange is detected by a sensor, and once all the ascorbic acid is consumed by a titrant, the change in potential of the sensor is observed, indicating the equivalence point of the titration.
For a food or beverage acidity determination, acid-base titration can also be monitored by the change in a color indicator such as phenolphthalein. Such a titration is performed using a strong base. As soon as the acid in a food sample is neutralized, a Phototrode sensor observes the exact color change, which corresponds to a change in potential. This change in potential provides the titration’s equivalence point. Phototrode sensors can also be used for precipitation or turbidity measurements.
METTLER TOLEDO offers a robust range of titration instrumentation, including automated titrators, that can help improve the accuracy and speed of your acidity titrations in F&B processing. Our various titration types and instrumentation can help you perform accurate and reliable acidity content determinations in the food and beverage industry.
Based on the type of titration as well as depending on the titrator used, we offer a broad portfolio of sensors to meet your food and/or drink quality control needs. Our sensors can help you with accurate total acidity measurements for foodstuffs and liquids such as wine and fruit juices.
Ensuring accuracy and repeatability in sample preparation is critical when seeking to meet quality control requirements and guarantee consumer safety in industries such as F&B.
To enhance sample preparation repeatability, accuracy, and speed, METTLER TOLEDO offers a suite of analytical instruments designed to help you increase throughput while reducing both time-to-result and per-sample processing costs.
Sample preparation is often liquid-based, and METTLER TOLEDO offers a number of systems for handling solutions ranging from aqueous to highly viscous and volatile.
Particularly in F&B where processing volumes can be as large as 20 mL or as small as 20 µL, we offer a comprehensive array of single- and multi-channel pipettes, benchtop systems and consumables to meet almost any sample preparation need.
Food industry grading often includes determining both acidity and moisture content to fulfill quality and safety parameters.
Our instruments help you perform fast and accurate moisture determinations with features such as integrated control limits, automatic data transfer and user guidance for ease of use, while our innovative QuickPredict functionality enables informed results prediction for faster moisture analysis and decision-making.
Accurate sample preparation is a crucial prerequisite for obtaining reliable measurements. With gravimetric sample preparation, both the solid and solvent are weighed-in, providing much more accurate solutions.
This helps to eliminate variability among samples and reduces out-of-specification results. You gain increased confidence in your analytical outcomes and more reliably meet safety and quality-control requirements.
We offer several application notes regarding acidity determination that focus on specific food and beverage products.
Noted in the table below, these helpful documents discuss specific sample types to help you obtain accurate acidity analyses across the food production value chain.
Acidity measurements can be made using pH and Titration. A pH meter measures the acid strength of a sample in terms of the concentration of H+ ions in a solution. Titrimetric analysis gives total titratable acid. Titration can be carried out using acid-base titration, redox titration or colorimetric titration.
Acidity measurement in food is a useful indicator of consistency, taste, and appearance across batches for quality control. Acidity analysis can also be used to monitor foods where the acidity changes over time, for example in yogurt production or brewing, or to test the freshness of certain foods.
Titratable acidity measurement can be important because it deals with the total acid concentration contained within a food (also called total acidity). pH measures acidity in terms of H+ ions present in the sample (also called active acidity).
The measurement of acidity in a solution is called pH. pH expresses the amount of hydrogen ion concentration (H+) in a liquid. If the concentration of hydrogen ions (H+) in the liquid is high, it is acidic. If the concentration is low, it is basic (alkaline). This means that when the concentration of hydrogen ions is measured, the acidity, neutrality, and alkalinity, as well as the respective degree of each can be determined.
Acid Dissociation Constant (Ka) measures the strength of an acid in solution.
Mathematically,
Ka=[A−][H+][HA],
where Ka s referred as a quotient of the equilibrium concentrations (in mol/L).
Yes, our pH sensors and meters support automation. Automation provides an excellent option for increasing productivity and efficiency in your lab. For further details regarding acidity determination and other automation options, please click here.
