Dissolved Oxygen

Question 1

Oxygen, O2

Answer 1

3rd most abundant chemical element. Comprises 21% of the atmosphere.

Question 2

Ions

Answer 2

Atoms that have fewer or more electrons, giving a negative or positive charge (cation or anion)

Question 3

Oxidiztion

Answer 3

Oxygen binding to a molecule, totally changing its properties

Question 4

Chill haze

Answer 4

Polyphenols and proteins bond together to form a colloid when beer is cold, dissolves when beer is warm. Dissolved oxygen helps these molecules bond.

Question 5

Permanent haze

Answer 5

When O2 increases chill haze, rate of conversion into permanent haze will also increase as the bonds between polyphenols and proteins become too big to be insoluble even in warm beer.

Question 6

Reduction in bitterness

Answer 6

Isomerized alpha acids become oxidized as time goes on, changing them and causing bitterness to decline with age

Question 7

Undesirable flavor compounds as a result of oxidization

Answer 7

Flavor compounds change or disappear when oxidized/bonded with oxygen. Some become unpleasant, eg lipids which produce E2 nonenal when oxidized (smells and tastes papery).

Question 8

Key control points: Separation

Answer 8

eg Centrifuge. Where DO pick up is possible, flush with CO2 and have seals protected by DAW.

Question 9

Key control points: Cold maturation

Answer 9

Yeast absorbing O2 is in low concentrations at this stage. As beer cools, O2 becomes more soluble, and less yeast is available to absorb it.

Question 10

Key control points: Clarification

Answer 10

eg Centrifuge after cold maturation before the bright tank. Lower temperatures = higher O2 solubility

Question 11

Key control points: Filtration

Answer 11

Powders, sheets, cartridges will contain O2 if not properly deaerated. Sheet filters leak beer continuously throughout the filter run, which can lead to O2 pick up.

Question 12

Key control points: Dilution

Answer 12

We must check O2 levels of DAW prior to dilution and O2 levels of diluted beer after.

Question 13

Key control points: Packaging

Answer 13

So many places and opportunities for O2 pick up. So many. Valves, unions, pumps, pipes, vessels, process gas.

Question 14

Optochemical Oxygen Sensor

Answer 14

A sample spread on a layer of plastic containing luminescent dye is illuminated. The oxygen in the sample absorbs some of the energy. The more oxygen, the less light will be measured by the photodetector.

Question 15

Electrochemical Oxygen Sensor

Answer 15

A cathode (negatively charged electrode) is separated from a sample by a membrane permeable by oxygen. Oxygen that crosses the membrane is given extra electrons. This sensor uses the number of electrons consumed to measure the amount of oxygen in the sample.

Question 16

Antioxidants

Answer 16

A compound that stops oxidization reactions, usually by becoming oxidized themselves. Sulphur dioxide and potassium metabisulphite most commonly used in brewing.