Noah Vinter
Lactic acid is an important component of alcoholic beverages, serving several functions and influencing the flavour, texture, and overall quality of the drink. The quantification of lactic acid in these beverages is essential for various reasons, including quality control, sensory evaluation, and ensuring product consistency. While it is often considered a contamination defect, lactic acid can also be desirable in specific beer styles when present at appropriate concentrations. The quantification process involves using analytical methods such as amperometric biosensors, enzymatic sensors, and calculations like titratable acidity to determine the concentration of lactic acid in wines, beers, and other alcoholic drinks.
| Characteristics | Values |
|---|---|
| Lactic acid in alcoholic beverages | Primarily found in beer and wine |
| Cause of lactic acid | Lactic acid bacteria contamination during the mashing stage of brewing, wild fermentation from environmental bacteria, poor sanitation practices, and contaminated raw materials |
| Quantification methods | Amperometric biosensor, enzymatic amperometric sensor, High-Performance Liquid Chromatography (HPLC), titratable acidity calculation |
| Lactic acid flavour standard | Used by sensory professionals, quality control professionals, brewers, beverage manufacturers, and professional tasters for evaluation, detection of contamination, and maintaining consistency |
| Lactic acid concentration | The concentration can vary depending on the beverage, but it is typically reported in g/L or % TA (g/100ml) |
| Benefits of lactic acid | Enhances safety, quality, and nutritional value, improves flavour and texture, and acts as a preservative |
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What You'll Learn
Using an amperometric biosensor
The quantification of lactic acid in alcoholic beverages is essential for several reasons. Firstly, it acts as a quality marker, influencing the safety and sensory characteristics of the product. For instance, in dry-fermented sausages, lactic acid concentrations above 800 mg/g prevent the growth of harmful bacteria, ensuring food safety. In alcoholic drinks, it serves multiple functions, including extending shelf life by inhibiting spoilage bacteria such as salmonella.
Amperometric biosensors provide a rapid, cost-effective, and reliable method for determining lactic acid content in real samples. This technique is particularly useful in wine and beer analysis, as it simplifies the traditionally time-consuming and expensive process of lactic acid detection.
The basic principle behind amperometric biosensors is the amperometric monitoring of oxygen consumption during lactic acid oxidation. This is achieved by immobilizing lactate oxidase (LacOx) on an oxygen electrode, with a voltage typically ranging from -500 to -600 mV. The resulting amperometric signal is recorded, and the reaction rate is correlated to the lactic acid concentration.
To optimize the biosensor's performance, different methods of lactate oxidase immobilization have been explored, including physical adsorption in Resydrol polymer and electrochemical polymerization in poly(3,4-ethylenedioxythiophene). The former exhibits a narrower dynamic range (0.004-0.5 mM lactate) and higher sensitivity (320 nA/mM), while the latter offers a wider dynamic range (0.05-1.6 mM) but lower sensitivity (60 nA/mM).
Additionally, nanocomposite electrodes consisting of multi-walled carbon nanotubes have been employed to enhance the biosensor's capabilities. These nanocomposites provide linearity over a broader range of lactic acid concentrations (5-340 μM) and offer a lower detection limit of 0.96 μM.
The development of amperometric biosensors has also extended to the creation of multi-biosensor systems, capable of simultaneously determining multiple analytes. For example, a glucose/fructose/ethanol multibiosensor and an L-lactate/L-malate/sulfite multibiosensor have been designed for food quality control applications.
In conclusion, amperometric biosensors offer a promising approach to quantifying lactic acid in alcoholic beverages, providing rapid, accurate, and cost-effective analysis. The versatility and adaptability of these biosensors make them a valuable tool for the beverage industry, ensuring product quality and safety.
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Calculating titratable acidity
The process involves using a strong base, typically sodium hydroxide (NaOH), to reach a basic pH of 8.2. This pH value is the industry standard in the US and Australia, as it is near the equivalence point for a lactic acid/sodium hydroxide reaction and is also where a titration dye, phenolphthalein, changes colour. At this pH, the solution contains equal amounts of NaOH and lactic acid. The specific steps involve taking a precise amount of degassed beer (e.g., 50 ml) in a beaker and gradually adding small amounts of NaOH (usually around 0.1-0.5 ml) while stirring and monitoring the pH until the solution reaches a pH of 8.2.
The TA can then be calculated using one of two methods, depending on whether the desired result is in millilitres of lactic acid per 100 grams of beer (Equation A) or grams of lactic acid per litre of beer (Equation B, more common).
Equation A: ml Lactic Acid per 100g beer
TA as lactic acid = ml 0.1M NaOH x 10/ml of beer x specific gravity
For example, if 50 ml of beer at a specific gravity of 1.010 required 5.6 ml of 0.1M NaOH to reach a pH of 8.2:
TA = 5.6 ml x 10/50 x 1.010 = 56/50.5 = 1.11
So, 1.11 ml of 1.0M alkali per 100 g of beer.
Equation B: g/L as a Specific Acid
1 – Total Acidity (mol/L) = ml x 0.1M / vol of beer
Using the same example:
Total Acidity (mol/L) = 5.6 ml x 0.1M / 50 ml = 0.0112 mol/L
Then, to convert to grams of lactic acid per litre:
G/L Lactic Acid = 0.0112 mol/L x (90g/mol) = 1.008g/L
The 90g/mol is a standard correction factor for lactic acid. This value can also be expressed as a percentage:
% Lactic Acid = 1.008g/L / 1,000g = 0.0018 x 100 = 0.18%
These calculations are based on the assumption that the sample is composed of 100% lactic acid, even though beer contains other acids as well. Therefore, it is important to note that TA does not directly measure the amount of lactic acid in the beer but rather expresses the measurement in terms of lactic acid.
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Lactic acid flavour standard
Lactic acid is the most prominent acid in beer, and it can also be found in other alcoholic beverages. While it is often considered a contamination defect, it can be a desirable flavour characteristic in certain beer styles like sour ales, lambics, and traditional farmhouse beers when present at appropriate concentrations. The distinctive sourness and acidic character reminiscent of yoghurt or sour milk can be identified and measured using the Lactic Acid Flavour Standard.
The Lactic Acid Flavour Standard is a tool used by professional tasters, brewers, and quality control specialists to ensure product quality, detect contamination early, and maintain consistent sensory standards. It is used to calibrate taste panels for consistent flavour identification, train new tasters to recognise lactic characteristics, establish threshold levels for quality control, and validate sensory results across different testing sessions. The standard consists of individually packaged capsules containing the lactic acid flavour, providing a consistent and accurate representation of the flavour.
Brewers and beverage manufacturers use the Lactic Acid Flavour Standard to monitor production processes and develop intentionally soured beer styles where lactic character is desirable. By accurately recognising and evaluating the lactic acid content, they can create consistent and desirable flavour profiles for their products. The standard helps in identifying unwanted lactic acid bacteria and maintaining product consistency.
Additionally, the Lactic Acid Flavour Standard is utilised by researchers studying fermentation science and microbiology. It serves as a reference standard for investigating lactic acid bacteria behaviour and developing contamination prevention strategies. By understanding the characteristics of lactic acid, researchers can explore its effects on the fermentation process and develop strategies to control its presence in beverages effectively.
The development of analytical methods, such as amperometric biosensors, has also improved the detection and quantification of lactic acid in alcoholic beverages, particularly in wines and beers. These methods offer rapid, cost-effective, and sensitive alternatives to traditional quantification techniques, facilitating the monitoring of lactic acid formation and ensuring product quality and safety. Overall, the Lactic Acid Flavour Standard and advanced analytical methods play crucial roles in the accurate evaluation and control of lactic acid in the alcoholic beverage industry.
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Lactic acid bacteria contamination
Lactic acid bacteria (LAB) are facultative anaerobes that use fermented carbon hydrates to produce lactic acid. LAB can be divided into at least 18 genera, with over 200 species. However, only a few of these species cause food spoilage. Lactobacillus and Pediococcus are the most hazardous bacteria in the brewing industry, causing around 70% of microbial beer spoilage incidents. They cause turbidity, a buttery odor, and sourness in alcoholic beverages due to the formation of diacetic acid, lactic acid, and extracellular polysaccharides, which render the beverages undrinkable.
In the wine industry, Pediococcus produces lactic acid through malolactic fermentation. Their secondary metabolites are volatile substances, so if they are rapidly propagated at the wrong time, they will affect the flavor of the wine and become spoilage microorganisms. LAB has also been known to cause cheese spoilage, producing unpleasant odors, gases, and the formation of white calcium lactate crystals on the surface due to nonstarter lactic acid bacteria (NSLAB).
Beer is considered an unfavorable growth substrate for most microorganisms due to its hop bitter acids, alcohol content, and low oxygen and nutrient content. However, a few microbes can still grow and cause spoilage, especially in unpasteurized or unfiltered craft beer. Lactobacillus brevis, a type of LAB, has been detected in spoiled beer and commercial active dry yeast. Other LAB species found in breweries include Staphylococcus sp., Enterobaceriaceae, and Acetobacter sp.
To prevent and control LAB contamination in alcoholic beverages, several detection and sanitation methods can be employed. Traditional culturing methods for detecting LAB are time-consuming, so novel rapid detection methods, such as PCR-DGGE and culture-dependent techniques, have been developed to identify contaminant LAB species and sources of contamination. Implementing sanitization plans and improving microbiological quality control using advanced culture media or different isothermal amplification methods can help prevent spoilage and ensure the safety and quality of the final product.
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Lactic acid in wine vs beer
Lactic acid is one of the most common organic acids found in alcoholic beverages, and it serves several functions. It is the most prominent acid in beer, and it is also commonly found in wine.
Lactic Acid in Wine
The measure of the amount of acidity in wine is known as "titratable acidity" or "total acidity", which refers to the test that yields the total of all acids present. The strength of acidity is measured by pH, with most wines having a pH between 2.9 and 3.9. The lower the pH, the higher the acidity. In wine tasting, the term "acidity" refers to the fresh, tart, and sour attributes of the wine, which are evaluated based on how well they balance the sweetness and bitterness of the wine, such as tannins.
During the winemaking process, bacteria convert the stronger malic acid, which is naturally present in grape must, into the softer lactic acid through malolactic fermentation (MLF). This process is standard for most red wines and some white grape varieties, such as Chardonnay. It imparts a "buttery" flavor and a rounder, fuller mouthfeel to the wine. Lactic acid bacteria (LAB) include three genera: Oenococcus, Pediococcus, and Lactobacillus. These bacteria convert both sugar and malic acid into lactic acid, with the latter being converted through MLF.
Lactic Acid in Beer
Lactic acid is the most prominent acid found in beer. It is typically measured using the American Society of Brewing Chemists' Beer Method 8, which helps brewers calculate the amount of lactic acid in solution. This method provides the concentration of lactic acid in grams per liter (g/L) or as a percentage of the total volume.
Quantification of Lactic Acid
The quantification of lactic acid in both wine and beer is important for quality control and to ensure the desired characteristics of the final product. Traditional methods for quantifying lactic acid can be time-consuming and costly. However, recent studies have proposed the use of amperometric biosensors for the rapid and cost-effective detection and quantification of lactic acid in wines and beers. These sensors employ lactate oxidase (LacOx) immobilized on an oxygen electrode, allowing for the determination of lactic acid concentration through oxygen consumption measurements.
In summary, lactic acid plays a significant role in both wine and beer, contributing to their acidity and overall sensory characteristics. The quantification of lactic acid using advanced biosensor technology offers a promising approach for efficient quality control in the beverage industry.
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Frequently asked questions
Lactic acid is an organic compound that develops naturally through bacterial fermentation or contamination during beverage production. It is the most prominent acid in beer.
Quantifying lactic acid in alcoholic beverages is important for several reasons:
- To ensure product quality and consistency.
- To detect bacterial contamination early on.
- To monitor production processes and prevent contamination, especially in intentionally soured beer styles where lactic character is desirable.
- To enhance the safety, nutritional value, and health-promoting properties of the beverage.
There are several methods available to quantify lactic acid in alcoholic beverages:
- Amperometric biosensors: These devices can rapidly and cost-effectively detect and quantify lactic acid in wines and beers by employing enzymatic amperometric sensors that use lactate oxidase (LacOx).
- High-Performance Liquid Chromatography (HPLC): This method is often used as a reference to validate other quantification techniques.
- Measuring Titratable Acidity: This method helps determine the exact amount of lactic acid in a beer by calculating the number of ml of lactic acid per 100g of beer or the concentration in grams per liter (g/L).
- Lactic Acid Flavour Standard: Used by professional tasters, brewers, and quality control specialists to identify, measure, and evaluate the level of lactic character in beverages.
The presence of lactic acid in alcoholic beverages, primarily in beer, can be attributed to:
- Lactic acid bacteria contamination during the mashing stage of brewing.
- Wild fermentation from environmental bacteria.
- Poor sanitation practices in brewing equipment.
- Contaminated raw materials, including malted grains and sugars.
The acceptable levels of lactic acid in alcoholic beverages depend on the specific type of beverage and the desired flavour profile. In some beer styles like sour ales, lambics, and traditional farmhouse beers, a certain level of lactic character is desirable. However, in most beverages, lactic acid is considered a contamination defect. The acceptable range for lactic acid concentration can vary, and it is important to adhere to the specific standards and regulations for different alcoholic beverages.
