Volatile acid

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In chemistry, the terms volatile acid (or volatile fatty acid (VFA)) and volatile acidity (VA) are used somewhat differently in various application areas.

Contents

Wine

In wine chemistry, the volatile acids are those that can be separated from wine through steam distillation. [1] Many factors influence the level of VA, but the growth of spoilage bacteria and yeasts are the primary source and consequently VA is often used to quantify the degree of wine oxidation and spoilage. [2]

Acetic acid is the primary volatile acid in wine, but smaller amounts of lactic, formic, butyric, propionic acid, carbonic acid (from carbon dioxide), and sulfurous acid (from sulfur dioxide) may be present and contribute to VA; [3] [4] [2] in analysis, measures may be taken to exclude or correct for the VA due to carbonic, sulfuric, and sorbic acids. [1] [5] Other acids present in wine, including malic and tartaric acid are considered non-volatile or fixed acids. Together volatile and non-volatile acidity compromise total acidity. [1]

Classical analysis for VA involves distillation in a Cash or Markham still, followed by titration with standardized sodium hydroxide, and reporting of the results as acetic acid. [6] [1] [7] Several alternatives to the classical analysis have been developed.

While VA is typically considered a wine flaw or fault, winemakers may intentionally allow a small amount of VA in their product for its contribution to the wine's sensory complexity. [3] Excess VA is difficult for winemakers to correct. [1] In the some countries, including the United States, European Union, and Australia, the law sets a limit on the level of allowable VA. [8] [1] [7]

Wastewater

In wastewater treatment, the volatile acids are the short chain fatty acids (1-6 carbon atoms) that are water soluble and can be steam distilled at atmospheric pressure - primarily acetic, proprionic, and butyric acid. [9] These acids are produced during anaerobic digestion. [10] [11] In a well functioning digester, the volatile acids will be consumed by the methane forming bacteria. [12] Volatile acid/alkalinity ratio is often measured as one indicator of a digester's condition. [13] The acceptable level of volatile fatty acids in environmental waters is up to 50,000 ppm. [14]

Volatile fatty acids can be analyzed by titration, distillation, steam distillation, or chromatography. [15] Titration provides approximate but relatively quick results; it is widely used by wastewater treatment plants to track a status of a digestor. Distillation similarly is used in wastewater treatment plants and produces approximate results; 15-32% of the VFAs are lost during distillation. Steam distillation can recover 92-98% of a samples VFA. This method is more precise than previous two methods, but requires about 4 hours to complete. Chromatography gives the most precise and accurate results. It is capable of qualitatively and quantitatively analyzing each individual VFA.

Physiology

In physiology, volatile acid (or respiratory acid) refers to carbonic acid, a product of dissolved carbon dioxide. In this context, volatile indicates that it can be expelled as a gas through the lungs. [16] [17] Carbonic acid is the only physiologically volatile acid; all other acids are physiologically nonvolatile acids (also known as a fixed or metabolic acids). Volatile acid results from the aerobic oxidation of substances such as carbohydrates and fatty acids. [18]

Butter

Volatile acid concentration can be used to detect adulteration of butter with less expensive fats. Butterfat has uncommonly high levels of volatile butyric and caproic acids, and mixing with fats from other sources dilutes the volatile acids. A measurement of the volatile acids is known as the Reichert Meissel value. [19] [20] [21]

Nutrition and digestion

In digestion, volatile acids or volatile fatty acids are short chain fatty acids. They are especially important in the digestion of ruminant animals, where they result from the action of rumen flora, and are abosorbed as an energy source by the animal.

Industrial hygiene

In workplace air samples, concentrations of hydrochloric, hydrobromic, and nitric acid may be monitored as hazardous volatile acids. [22]

See also

Related Research Articles

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An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is often written as R−COOH or R−CO2H, sometimes as R−C(O)OH with R referring to an organyl group, or hydrogen, or other groups. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Ester</span> Compound derived from an acid

In chemistry, an ester is a compound derived from an acid in which the hydrogen atom (H) of at least one acidic hydroxyl group of that acid is replaced by an organyl group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well, but not according to the IUPAC.

<span class="mw-page-title-main">Titration</span> Laboratory method for determining the concentration of an analyte

Titration is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte. A reagent, termed the titrant or titrator, is prepared as a standard solution of known concentration and volume. The titrant reacts with a solution of analyte to determine the analyte's concentration. The volume of titrant that reacted with the analyte is termed the titration volume.

<span class="mw-page-title-main">Vinegar</span> Liquid consisting mainly of acetic acid and water

Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains from 5% to 18% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to ethanol using yeast and ethanol to acetic acid using acetic acid bacteria. Many types of vinegar are made, depending on source materials. The product is now mainly used in the culinary arts as a flavorful, acidic cooking ingredient or in pickling. Various types are used as condiments or garnishes, including balsamic vinegar and malt vinegar.

<span class="mw-page-title-main">Winemaking</span> Production of wine

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Malolactic conversion is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is most often performed as a secondary fermentation shortly after the end of the primary fermentation, but can sometimes run concurrently with it. The process is standard for most red wine production and common for some white grape varieties such as Chardonnay, where it can impart a "buttery" flavor from diacetyl, a byproduct of the reaction.

<span class="mw-page-title-main">Maceration (wine)</span> Winemaking process where grape skins and seeds are kept in contact with the juice

Maceration is the winemaking process where the phenolic materials of the grape—tannins, coloring agents (anthocyanins) and flavor compounds—are leached from the grape skins, seeds and stems into the must. To macerate is to soften by soaking, and maceration is the process by which the red wine receives its red color, since raw grape juice is clear-grayish in color. In the production of white wines, maceration is either avoided or allowed only in very limited manner in the form of a short amount of skin contact with the juice prior to pressing. This is more common in the production of varietals with less natural flavor and body structure like Sauvignon blanc and Sémillon. For Rosé, red wine grapes are allowed some maceration between the skins and must, but not to the extent of red wine production.

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The Kjeldahl method or Kjeldahl digestion (Danish pronunciation:[ˈkʰelˌtɛˀl]) in analytical chemistry is a method for the quantitative determination of a sample's organic nitrogen plus ammonia/ammonium. (NH3/NH4+). Without modification, other forms of inorganic nitrogen, for instance nitrate, are not included in this measurement. Using an empirical relation between Kjeldahl nitrogen and protein, it is an important method for indirectly quantifying protein content of a sample. This method was developed by Johan Kjeldahl in 1883.

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The Reichert value is a value determined when examining fats and oils. The Reichert value is an indicator of how much volatile fatty acid can be extracted from a particular fat or oil through saponification. It is equal to the number of millilitres of 0.1 normal hydroxide solution necessary for the neutralization of the water-soluble volatile fatty acids distilled and filtered from 5 grams of a given saponified fat.

Short-chain fatty acids (SCFAs) are fatty acids of two to six carbon atoms. The SCFAs' lower limit is interpreted differently, either with one, two, three or four carbon atoms. Derived from intestinal microbial fermentation of indigestible foods, SCFAs in human gut are acetic, propionic and butyric acid. They are the main energy source of colonocytes, making them crucial to gastrointestinal health. SCFAs all possess varying degrees of water solubility, which distinguishes them from longer chain fatty acids that are immiscible.

<span class="mw-page-title-main">Fermentation in winemaking</span> Wine making process

The process of fermentation in winemaking turns grape juice into an alcoholic beverage. During fermentation, yeasts transform sugars present in the juice into ethanol and carbon dioxide. In winemaking, the temperature and speed of fermentation are important considerations as well as the levels of oxygen present in the must at the start of the fermentation. The risk of stuck fermentation and the development of several wine faults can also occur during this stage, which can last anywhere from 5 to 14 days for primary fermentation and potentially another 5 to 10 days for a secondary fermentation. Fermentation may be done in stainless steel tanks, which is common with many white wines like Riesling, in an open wooden vat, inside a wine barrel and inside the wine bottle itself as in the production of many sparkling wines.

<span class="mw-page-title-main">Acids in wine</span>

The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeast during fermentation and protecting the wine from bacteria. The measure of the amount of acidity in wine is known as the “titratable acidity” or “total acidity”, which refers to the test that yields the total of all acids present, while strength of acidity is measured according to pH, with most wines having a pH between 2.9 and 3.9. Generally, the lower the pH, the higher the acidity in the wine. There is no direct connection between total acidity and pH. In wine tasting, the term “acidity” refers to the fresh, tart and sour attributes of the wine which are evaluated in relation to how well the acidity balances out the sweetness and bitter components of the wine such as tannins. Three primary acids are found in wine grapes: tartaric, malic, and citric acids. During the course of winemaking and in the finished wines, acetic, butyric, lactic, and succinic acids can play significant roles. Most of the acids involved with wine are fixed acids with the notable exception of acetic acid, mostly found in vinegar, which is volatile and can contribute to the wine fault known as volatile acidity. Sometimes, additional acids, such as ascorbic, sorbic and sulfurous acids, are used in winemaking.

<span class="mw-page-title-main">Acetic acid</span> Colorless and faint organic acid found in vinegar

Acetic acid, systematically named ethanoic acid, is an acidic, colourless liquid and organic compound with the chemical formula CH3COOH. Vinegar is at least 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water. It has been used, as a component of vinegar, throughout history from at least the third century BC.

This glossary of winemaking terms lists some of terms and definitions involved in making wine, fruit wine, and mead.

<span class="mw-page-title-main">Ripeness in viticulture</span> How the term "ripe" is used in viticulture and winemaking

In viticulture, ripeness is the completion of the ripening process of wine grapes on the vine which signals the beginning of harvest. What exactly constitutes ripeness will vary depending on what style of wine is being produced and what the winemaker and viticulturist personally believe constitutes ripeness. Once the grapes are harvested, the physical and chemical components of the grape which will influence a wine's quality are essentially set so determining the optimal moment of ripeness for harvest may be considered the most crucial decision in winemaking.

<span class="mw-page-title-main">Yeast in winemaking</span> Yeasts used for alcoholic fermentation of wine

The role of yeast in winemaking is the most important element that distinguishes wine from fruit juice. In the absence of oxygen, yeast converts the sugars of the fruit into alcohol and carbon dioxide through the process of fermentation. The more sugars in the grapes, the higher the potential alcohol level of the wine if the yeast are allowed to carry out fermentation to dryness. Sometimes winemakers will stop fermentation early in order to leave some residual sugars and sweetness in the wine such as with dessert wines. This can be achieved by dropping fermentation temperatures to the point where the yeast are inactive, sterile filtering the wine to remove the yeast or fortification with brandy or neutral spirits to kill off the yeast cells. If fermentation is unintentionally stopped, such as when the yeasts become exhausted of available nutrients and the wine has not yet reached dryness, this is considered a stuck fermentation.

References

  1. 1 2 3 4 5 6 Zoecklein, B. W. (2012). "Volatile acidity". Production Wine Analysis. United States: Springer US. ISBN   9781461581482.
  2. 1 2 Gump, B. H.; Nury, F. S.; Zoecklein, B.; Fugelsang, K. C. (1995). "Volatile Acidity". Wine Analysis and Production. Netherlands: Springer.
  3. 1 2 Waterhouse Lab (March 2019). "What's in Wine?: Volatile Acidity". UC Davis. Retrieved 2022-12-30.
  4. ↑ "Volatile acidity" (PDF). Grapegrower & Winemaker. No. 648. Australia: Winetitles Media. January 2018. Retrieved 2022-12-30.
  5. ↑ International Organisation of Vine and Wine (2022). "Volatile Acidity (Type-I)". Compendium of International Methods of Wine and Must Analysis. Paris: OIV. ISBN   978-2-85038-052-5.
  6. ↑ "History of the Cash Still and the Volatile Acidity Still (RD80)". Adams & Chittenden Scientific Glass Coop. Retrieved 2022-12-30.
  7. 1 2 Buick, D.; Holdstock, M. (2003). "The relationship between acetic acid and volatile acidity". AWRI Technical Review. 143: 39–43.
  8. ↑ Kelly, Molly; Gardener, Denise M. (2020). "What Is Volatile Acidity?". Penn State Extension. Retrieved 2022-12-30.
  9. ↑ American Public Health Association, American Water Works Association, Water Environment Federation (2018). "5560 Organic and Volatile Acids". Standard Methods For the Examination of Water and Wastewater (23rd ed.).{{cite book}}: CS1 maint: multiple names: authors list (link)
  10. ↑ Office of Water Programs. "Volatile acids". Glossary of Water and Wastewater Terms. California State University, Sacramento.
  11. ↑ Wastewater Management Program (2022). "Volatile Acids and Alkalinity". Laboratory Manual for Wastewater Analyses. Department of Environmental Conservation, Agency of Natural Resources, State of Vermont.
  12. ↑ Schnaars, Ken (2012). "What every operator should know about anaerobic digestion". Water Environment & Technology. No. December.
  13. ↑ Hauser, B. (2018). "Volatile Acids/Alkalinity". Practical Manual of Wastewater Chemistry. CRC Press. ISBN   978-1-351-42259-8.
  14. ↑ Determination of Volatile Fatty Acids in Environmental Aqueous Samples, by Faculty of Chemistry, University of Gdańsk
  15. ↑ (Water Environment Research, page 53-59, Anderson, G.K. and Yang G. (1992))
  16. ↑ Brandis, Kerry (2015). "Acid-Base Balance". Acid Base Physiology . Retrieved 2022-12-31.
  17. ↑ TheFreeDictionary (2009). "volatile acid". Medical Dictionary. Farlex and Partners.
  18. ↑ Johnston, D. G.; Alberti, K. G. M. M. (1983-07-01). "Acid-base balance in metabolic acidoses". Clinics in Endocrinology and Metabolism. Metabolic Acidosis. 12 (2): 267–285. doi:10.1016/S0300-595X(83)80041-3. ISSN   0300-595X. PMID   6409464 . Retrieved 2022-12-31.
  19. ↑ Wiley, H. W. (1907). "Milk and Milk Products and Oleomargarine". Foods and Their Adulteration: Origin, Manufacture, and Composition of Food Products; Description of Common Adulterations, Food Standards, and National Food Laws and Regulations. Washington, DC: DigiCat.
  20. ↑ Rutz, W. M. D.; Martin, W. H.; Whitnah, C. H. (1955-04-01). "Reichert-Meissl Numbers of Butterfat from Commercial Products Produced in Kansas1". Journal of Dairy Science. 38 (4): 387–390. doi: 10.3168/jds.S0022-0302(55)94989-4 . ISSN   0022-0302.
  21. ↑ The American Oil Chemists' Society (2020). "AOCS Official Method Cd 5-40: Reichert-Meissl, Polenske, and Kirschner Values, Modified AOAC Methods". Official Methods and Recommended Practices of the AOCS (7th ed.). American Oil Chemists' Society. ISBN   978-1-63067-060-3.
  22. ↑ Andrews, Ronnee; Fey O’Connor, Paula, eds. (2020). "Volatile Acids by Ion Chromatography: METHOD 7907". NIOSH Manual of Analytical Methods (5th ed.). National Institute for Occupational Safety and Health (NIOSH), Centers of Disease Control and Prevention, U.S. Department of Health & Human Services.
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