Fermentation And Technology

Question 1

Chemical symbol of yeast taking up simple sugars and converting them to alcohol and CO2

Answer 1

C6H12O6(glucose) -> 2C2H5OH (ethanol) + 2CO2 (carbon dioxide)

Question 2

Adenosine triphosphater ATP

Answer 2

The reaction in which sugar is broken down glycolysis are primarily oxidation’s, which release energy.
-cells retain some of this energy as ATP

Question 3

Diacetyl

Answer 3

Formed by yeast during fermentation. It is later re absorbed and broken down to products which are less flavoursome.
- in modern, more rapid processes where saving time is critical, the re-absorption phase occurs towards the end of active fermentation. As the rate of diacetyl reduction is temperature dependant, fermentations are kept warm during this phase. For this reason, this is often called a warm stand, rest, or a diacetyl/VDK stand.

Question 4

Covert present gravity to degrees Plato

Answer 4

The Plato is roughly a quarter of the present gravity

Question 5

Glycolysis

Answer 5

Pathway used to break down glucose and simple sugars
- generates energy that can be stored and used in other reactions eg. building new cell materials
- yeast makes 2 molecules of ATP for each molecule of glucose used.

Question 6

Saccharometer

Answer 6

A hydrometer calibrated for the range of densities used in brewing; a weighted glass bulb with a scale

Question 7

Fermentation: Lag phase

Answer 7

Fermentation is started by adding yeast, which takes some time to adapt to the new environment of warm oxygenated wort. O2 is taken up early on to make lipids and sterols, which are shared daughter cells. Eventually 02 is depleated and lipids drop off; growth stops.

Question 8

Fermentation: log phase

Answer 8

“Exponential phase”, most changes occur
-yeast grows the fastest, max sugar uptake, max alcohol and co2 formation
-greatest drop in pH

Question 9

Fermentation: deceleration phase

Answer 9

-limit yeast growth
-when substances essential for yeast growth run out

Question 10

Fermentability calculation

Answer 10

Initial gravity - fed end gravity / initial gravity x 100 = wort fermentability (%)

Question 11

Fermentation:stationary phase

Answer 11

Decrease in gravity stops.
- all fermentable sugars used up
- yeast stops growing and begins to flocculate.

Question 12

Fermentation: end gravity

Answer 12

Attenuation gravity
- residual gravity is mainly the dextrins that brewing yeast cannot use.

Question 13

Flocculation

Answer 13

Is where cells bing to each other to form large clumps called flocks.

Question 14

Fermentation pH

Answer 14

The initial usually around 5.9-5.2. Drops to about 4.0, but varies with different beers and is typically 3.8-4.4

Question 15

Wort composition

Answer 15

Influences total yeast growth and beer flavour
- oxygen solubility decreases a with increase in wort concentration.

Question 16

Temperature

Answer 16

Faster fermentation at higher temps
- no effect in total yeast growth, just rate

Question 17

Pitching rate

Answer 17

At low/medium values, increase in pitching rate increases fermentation rate

Question 18

Wort oxygenation

Answer 18

Increases fermentation rate and yeast growth
-very high pitching reduces total yeast growth, as there is less O2 per cell.

Question 19

Harmocytometer

Answer 19

The slide with the engraved grid for easier counting under a microscope

Question 20

Viability calculation

Answer 20

Number of live cells/ total cell number (x 100)

Question 21

Recommend pitching rate for 15*P

Answer 21

15 million cells p mL