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Acidity
* Most acidity causes irritation
  - skin irritation
* Some acidity causes death.
* affects cation exchange and the chemical form of minerals.
* also mobilizes some metals such as radium, copper, zinc, nickel and lead
  - preserves the freshness and allows the wine to keep
* balances the body and offers live aftertaste.
* can also modify ecosystem processes such as decomposition and the flow of nutrients
  - balance sweetness, and is necessary for wines to age well
  - cause paper, cloth, and leather to become brittle and discolour
  - hide sweetness
  - result in irreparable damage to paper such as yellowing and increase the brittleness
* desirable characteristic in coffee.
* has significantly affected water quality and fish species in certain streams.
* helps to maintain balance and structure throughout the distillation process.
* increases as the pH gets lower.
* is akin to the dryness of wine
  - also important in terms of structure
  - an indication of the absence of lime or other alkaline material
  - characteristic of high-grown coffees
  - due to the release of organic acids during anaerobic decomposition
  - measured by pH, the negative logarithm of the hydrogen ion concentration in a liquid
* is measured on a scale called pH, as shown in the figure below
* is measured on the pH scale
  - per-hydrogen, or pH scale
  - using the pH scale
  - with a pH meter or with pH paper strips
  - needed to balance the other flavours of fruit and sweetness
* is one of the primary traits of wines that age well
  - worst enemy of paper which can be removed by de-acidification
  - primary cause of paper deterioration
  - probably the most important single factor affecting the permanence of archival materials
  - reduced by the volatilization and denitrification of nitrogen
  - sour
* is the fertile soil for parasites and degenerative diseases
  - sharp, lively quality of all high-grown coffees
  - true measure of a coffee's ultimate taste
* is used as a proxy for volcanic eruptions
  - to keep the wine from becoming flabby
* often points to industrial pollution.
* refers to the ease with which a compound donates a hydrogen ion.
* regulates the solubility of many minerals.
* runs right through the fruit, prolonging the fruit flavors in the mouth.
* tends to have a much higher incidence in highly emotional and nervous individuals.

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Gastric acidity
* converts the cyst back into the active form.
* influences the blood response to a beta-carotene dose in humans.
* plays an important role in preventing cholera infection.

High acidity
* can be okay in white wines, but is very disrupting in red wines.
* combined with the presence of dissolved gases makes the source corrosive.
* dissolves many fibers and dyes.

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Soil acidity
* affects many other crops as well.
* determines flower colour in some varieties.
* encourages mineral decomposition and the overall development of the soil profile.
* has a significant impact on the availability of nutrients.
* is adjusted upward by adding liming materials to the soil
  - measured using a pH scale
  - natural or comes from acid rain, heavy use of fertilizers
  - serious in tidal swamps because of acid sulfate soils
* main cause of reduced productivity in farmland.
* major contributor to soil degradation and reduced plant production
  - environmental stress factor which limits the growth of most crops
* perennial problem because of Mississippi's warm, rainy climate.

Tart acidity
* dominates light fresh-fruit sweetness.
* surrounds fresh if rather simple cherry fruit on the palate.