Unit 4 Molasses

Question 1

Describe the the flavour of light rums

Answer 1

Delicate and subtle flavour

Question 2

What yeast is used for light rum?

Answer 2

Saccharomyces cerevisiae. This fermentation is similar to that carried out for the production of neutral spirits

Question 3

What is the main selection criteria of yeast for light rum?

Answer 3

Ability to produce a high alcohol yield at the end of fermentation
Good tolerance of fermentation temperature. Fermentation temperatures are generally maintained around 32-34C but some strains can ferment as high as high as 37C

Good tolerance to osmotic stress and the fermentation system in general

A low production of flavour compounds (congeners)

High invertase activity which is essential for sucrose/molasses fermentation (invertase converts sucrose into fructose and glucose)

Question 4

What are pure yeast cultures

Answer 4

One strain that is grown with as little contamination with microorganisms as possible.

Question 5

What is propagation?

Answer 5

is the process used to grow new yeast cells for use in fermentation. It is usually done under aerobic (air is present) conditions. Yeast suppliers propagate yeast in a liquid containing molasses and nutrients.

Question 6

What is flocculation?

Answer 6

is the clumping together of yeast cells once the sugar in the fermenting liquor is converted to alcohol

Question 7

What is inculation?

Answer 7

The transfer of the yeast into the unfermented liquor to start the fermentation process. It is also called pitching.

Question 8

Describe pure yeast culture in propagation

Answer 8

Propagated in a propagator or pre fermenter vessel
CY is added to molasses and nutrients in the pre fermenter and multiplies
Oxygen is supplied to promote growth of the new yeast cells
When required cell concentration is achieved in the pre fermenter, up to 90% of the yeast volume is added to a fermentation vessel,
PF is then refilled (topped up) with molasses and the yeast starts to grow again
Process can be repeated several times

Question 9

Describe the yeast recycling process

Answer 9

Yeast is removed from molasses by sedimentation or centrifugation before being treated or conditioned.
In the conditions step, the yeast inoculum is acid washed to a pH of about 2.2-2.5 using incremental addition of phosphoric acid.
Acid washing reduces bacteria in the yeast.
The recycled yeast can also be treated with penicillin.

Question 10

How often do they dump the yeast after recycling?

Answer 10

2-6 months

Question 11

What are the two ways dried yeast can be used?

Answer 11

Can be added or pitched directly to the fermenter at the start of the fermenter filling process
Or rehydrated and propagated in a pre fermenter before being added to the fermenter.

Question 12

How long of a shelf life does dried yeast have?

Answer 12

3 years

Question 13

For light rum fermentation, what must we achieve?

Answer 13

Rapid fermentation

Absence of microbial contamination

Good alcohol yield

Production of acceptable flavour compounds

Question 14

Why must we control the temperature in light rum fermentation?

Answer 14

Must control temperature, to ensure the light run fermentation produces acceptable congeners as some unwanted sulphurous compounds can be produced when the fermentation temperature is too high.

Question 15

We control temperature in light rum fermentations to produce acceptable congeners, what other affect does temperature have if not controlled?

Answer 15

as sulphurous compounds can be produced in fermentation when the temperature is too high, which can have a big effect on flavour. The maximum temp is generally about 33C but can be as low as 28C.

Question 16

When and why are antibiotics used in fermentation?

Answer 16

to control and prevent microbiological contamination & are used at the propagation stage, and in some cases they are also used in the fermenter.

Antibiotics include penicillin, chlorine dioxide and quaternary ammonium compounds

Question 17

What contributes to the desired flavour and congener profile of heavy rum

Answer 17

Microorganisms

Question 18

What are the fermentation types in heavy rum?

Answer 18

Spontaneous fermentation using yeasts and bacteria already present in the molasses.
Spontaneous fermentation supplemented by the use of dunder.
Rum fermentation using a selected strain of saccharomyces cerevisiae yeast
Rum fermentation using a selected straight of schizosaccharomyces pombe yeast
Rum fermentation supplementing the use of the two aforementioned yeast with bacteria such as clostridium saccharobutyricum

Question 18

Describe spontaneous fermentation (heavy rums)

Answer 18

the fermentation that occurs in diluted molasses due to the microorganisms naturally present.

the organisms compete with one another to convert the available nutrients . This can reduce production costs since the microorganisms do not have to be purchased or grown However can cause low fermentation efficiency and yield

helps develop the complex flavours and aromas of the heavy rum

Question 19

why is spontaneous fermentation variable?

Answer 19

because the mix of bacteria and yeast in the molasses is not always the same.

Question 20

Describe fermentation using selected yeast strains

Answer 20

Heavy rum fermentations using selected yeast strains are more reliable than SF. They allow for a more controlled fermentation.

Strains of yeast species SP & SC occur naturally in molasses and dunder.

Question 21

What is the temperature and brix of molasses? (HR)

Answer 21

less than 22 brix and 27-33C

Question 22

Describe fermentation using bacteria (HR)

Answer 22

Adding bacteria to the fermentation produces organic acids such as acetic, propionic and butyruc acid. These acids react with alcohols to produce esters and hence contribute to the complex flavour.

Question 23

Describe fermentation using bacteria supplementation

Answer 23

the bacterial inoculum is added after the yeast fermentation has started. This can be done 6-12 hrs after fermentation has started when alcohol level is to be about 3%.

It’s found that the best yield and rum flavour is achieved with a yeast:bacteria cell count ratio of 5:1

Question 24

Why does molasses require additional nutrients?

Answer 24

yeast needs nutrients to grow and ferment effectively. Dammonium sulphate is commonly added. Some commercial nutrient products (yeast foods) containing inorganic components such as magnesium, calcium, potassium and zinc, may also be beneficial for rapid and complete fermentation. The use of urea as a nitrogen source should be avoided, as this is a know precursor of ethyl carbmate

Question 25

Describe batch fermentation (dark rum)

Answer 25

molasses & yeast are added to the fermentation vessel to start fermentation. The molasses is prepared at pH of about 4.5 to minimise early bacterial growth. Recommended that the brix is at 18 for a faster fermentation start lets yeast outcompete bacteria. molasses added to FV and is inoculated with the chosen yeast strain. The temp is maintained below 34C. Fermentation continues until an abv of 8-9% is reached

Question 26

What is incremental feeding fermentation?

Answer 26

A half full fermentation vessel, which is fermenting at 13 Brix is topped up with extra molasses at about 30-35 brix. Helps to achieve a high alcohol yield and a rapid start to the fermentation process. ABV of >11% can be achieved & can control fermentation temp

Question 27

Other than the yeast recycling process, what other kinds of yeast can be used?

Answer 27

Commercially dried yeast is used in light rum fermentations. Dried yeast has a longer shelf life (usually three years) than other yeast formats.

Question 28

What other yeast foods are beneficial to add for rapid fermentation? (Dark rums)

Answer 28

magnesium, calcium, potassium and zinc.

Question 29

What is the most effective ratio of yeast:bacteria for dark rum fermentation?

Answer 29

5:1