Vinegar

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Vinegar is approximately 5% by volume acetic acid with the bulk of the remainder being water.

Acetic Acid density is 1.049g/ml, or 1049g/L.
Vinegar is 5% acetic acid. Calculate: 5% * 1049g/L = 52.45g/L of acetic acid in vinegar.
Acetic Acid molar mass is 60. 52.45
60
= 0.874M/L or 7
8
molar)

Uses

Primary

  • Pickling brine
  • An acidic solution (pH near 2.4)

Secondary

Natural occurrence

  • Acetic acid is produced by many living things, both as a metabolite and a waste product.

Hazards

Production

Bioproduction

Acetobacter are ubiquitous bacteria which consume oxygen and convert sugars and alcohols into acetic acid and water as part of their metabolism:

CH3CH2OH + O2 CH3COOH + H2O

Pot fermentation

Put dilute ethanol in a pot. Let nature take its course.

  1. Place dilute ethanol in a container with a large open top.
  2. IF you have a mother-of-vinegar from a prior vinegar fermentation
    1. Add some of the mother-of-vinegar to the ethanol
  3. ENDIF
  4. Cover the top of the container with cloth, a woven mat, a seive or some other device that will allow the airborn acetobacter to enter while keeping pests (insects and animals) out.
  5. Wait several days to a week
    Check: It should start to smell of vinegar within a few days, and the scent should grow stronger over time.
    Check: A mother-of-vinegar (slimy clear or brown material) may form atop the vinegar
  6. IF a mother-of-vinegar forms
    1. Skim it off the mixture
    2. Retain the residue, storing it atop other dilute ethanol
  7. ENDIF
  8. Filter
  9. Discard residue. It's mostly organic dreck
  10. Retain filtrate. It is vinegar.

Aerated fermentation

This is essentially the same as above, except that the solution is regularly circulated over an aeration material. Caveat: This process can decrease, rather than increase, the yield if too much ethanol is lost to evaporation.

  1. Prepare an aeration tower (a 30cm high by 10cm wide pipe is sufficient for a small batch)
  2. Place the tower on a grate sufficient to keep out pests and aeration material
  3. Fill the tower with aeration material (inert high-surface-area objects like broken pottery or wood shavings)
  4. Place the grate atop a container capable of holding the entire batch of ethanol/vinegar.
  5. Fill the container with dilute ethanol as above
  6. Periodically drain the liquor from the container and pour it atop the tower, allowing it to drain back into the main container
    NB: The more frequently the liquor is circulated, the more rapidly it will convert to vinegar.

In practice the conversion is bound on available oxygen rather than alcohol. The rate of conversion is greatly increased by aerating the alcohol solution. One such method circulates the mother liquor over a tall cylinder filled with wood shavings or even pottery shards. This introduces more oxygen to the liquor and subsequently the production of acetic acid.

Extraction

From wood distillates

Wood distillation produces acetic acid as a major volatile component.

Concentration

A 5% concentration may not be that useful, unless the acetic acid can be concentrated.

via freezing

The freezing point of vinegar is lower than that of pure water.

  1. Freeze the vinegar completely, or nearly completely
  2. Drain the container of any liquid, then allow the frozen solution to melt slowly. The parts of the ice "rich" in acetic acid will melt first, giving a more concentrated acid solution
    NB: This will also remove some kinds of impurities, which will remain trapped in the ice
  3. Filter the resulting fluid, if necessary
  4. Discard the residue
  5. The filtrate is a more concentrated solution of vinegar.

via distillation

Water and acetic acid have boiling points at 100C and 118C respectively. While you could theoretically keep the solution at 105C and boil off all the water and none of the acid, vapor pressure for both is nonzero, so there are practical limits on the degree to which they can be separated by distillation. The literature says vinegar can be concentrated by distillation(s) to near 95% acetic acid, but the returns on subsequent distillations fall off asymtotically.

  1. Place vinegar in the alembic
  2. Place the alembic in an oil bath
  3. Raise the temperature of the bath to 105-110°C and distill until no more fluid is distilled
  4. Discard the contents of the receiver (water, perhaps with some small amount of vinegar)
  5. In the alembic is a more concentrated solution of vinegar.

via diethyl ether

Acetic acid may be extracted from a dilute aqueous solution (such as vinegar) using ether. Ether will not dissolve into water, but ascetic acid dissolves more readily in ether, leaving only about 0.1% in the water.

  1. Combine vinegar and ether in a sealed container
  2. Agitate strongly
  3. Allow the solution to settle (and separate)
  4. Decant the supernatant (ether) into an alembic
  5. Discard the rest (water, perhaps with some small amount of vinegar)
  6. distill the ether into the receiver and recycle
  7. The contents of the alembic are concentrated acetic acid

See Also

References