Unit 4 - Grape

Question 1

What are the two key attributes of must compared to other fermentations?

Answer 1

It has a relatively high starting sugar concentration
It has a low pH value

Question 2

Wat is the starting gravity of wort in most whiskies vs must for brandy?

Answer 2

whisky - 1.065-1.070 (16-17brix)

Brandy 1.80 or higher (19.3 brix)

the higher the sugar concentration, the increase of osmotic stress on the yeast which can produce more esters

Question 3

How long can Brandy fermentation take?

Answer 3

up to two weeks

Question 4

What are the factors that may be analysed by the winemaker before fermentation?

Answer 4

suagr concentration
pH
The amount of acids in the juice
for any visible bacteria or non saccharomyces
Nitrogen content YAN (measure of amino acids ammonium ions and peptides present ideal YANlevel is 150-200mg/L)
cell count of any worrying organisms

Question 5

What are the most common nutrient products on the market?

Answer 5

DAP (di-ammonium phosphate) = inexpensive however it only provides nitrogen

Question 6

When considering yeast for fermentation in brandy production, what are the two options chosen?

Answer 6

select a commercial strain suitable for wine spirits production

Use yeasts naturally present in must or on the grapes for fermentation (spontaneous or natural)

Question 7

What are some of the important species usually present on a grape skin?

Answer 7

Metschnikoia
Torulaspora delbrueckii
Brettanomyces
saccharmyces spp

Question 8

What is the pattern of spontaneous fermentation?

Answer 8

once grapes are crushed, sugar is immediately available to the wild yeast

fermentations are started by non saccharomyces yeasts

Saccharomyces yeasts steadily grow in number and take up nutrients

after 24-48 hrs saccharomyces become the dominant organisms in the fermentation

Question 9

fermentation vessels for must should be:

Answer 9

solid construction and made with food grade materials such as steel food grade plastic wood glass or concrete
easy to clean
taller than they are wide. height to width ratio of at least 2:1
cooled to prevent overly warm temperatures from occurring in the wine and wine spoilage before distillation

Question 10

How much cells does dried yeast contain?

Answer 10

10 billion cells per g

Question 11

Describe temperature in must fermentation

Answer 11

low temps slow it down while higher temps speed it up
higher temps increase ester development
Red wines are usually fermented above 20 C while white wines are usually fermented below 15C

Question 12

How long is brandy wine fermentation & why?

Answer 12

can last as long as two weeks or up to several months.

A higher starting gravity means more sugars need to be fermented
lower pH levels can slow the fermentation
heating options may not be available during colder months
may be a nutrient deficiency which the distiller is not allowed to correct
May not contain many yeast cells

Question 13

What do winemakers use to make sure fermentation is complete?

Answer 13

hydrometer as SG gravity normally finishes at 0.990 or less.
They also use the clinitest to assess the amount of sugars left in the must which changes the colour of the sample wine & it is then compared to a chart from which the amount of the residual sugar in the wine can be estimated.

Question 14

What is malolactic fermentation?

Answer 14

Where malic acid is converted to lactic acid through the removal of carbon dioxide
Malic acid is a very tart tasting acid; lactic acid is gentler on the palate.
Not actually a fermentation, as no alcohol is formed. The release of CO2 gives the impression that some fermentation is taking place, but actually it’s not.

Question 15

Describe the aroma of diacetyl

Answer 15

butterscotch & comes from the bacteria Oenococcus oeni, Lactobacillus and Pediococcus

Question 16

How does malolactic fermentation start?

Answer 16

started by the winemaker through inoculating the must or wine with Oenococcus oeni.they can allow it to proceed naturally due to lactic acid bacteria already present on the grape skins or in the must.
Winemakers typically use enzymatic assay kits to check if the malic acid has been converted to lactic acid.

Question 17

What organisms can spoil wine?

Answer 17

Acetobacter - forms films on top of wine exposed to air. These bacteria convert ethanol into acetic and ethyl acetate resulting in a vinegar like aroma in the wine
Kloeckera apiculata - naturally present on grapes & if nor controlled it can produce large amounts of ethyl acetate which has a solvent like aroma
Brettanomyces spp - generally not a problem for distillery as they take several month to produce unwelcome flavour compounds
Lactic acid bacteria - ome strains of Pediococcus spp., Lactobacillus spp., and Lactococcus spp. can cause problems including, but certainly not limited to, diacetyl production, and excessive ethyl acetate levels.

Question 18

Why is it important to measure yan levels?

Answer 18

It’s possible to add too many nutrients. Higher amino acids levels can increase the amount of fusel alcohols (higher alcohols) that the yeast produces, which affects the flavour of the spirit produced.

Question 19

Describe Metschnikowia

Answer 19

A genus of yeasts that do not produce a lot of alcohol but do add fruity aromas before Saccharomyces yeasts have multiplied sufficiently to take over fermentation.

Question 20

Describe Torulaspora delbrueckii

Answer 20

this yeast species produces pleasant aromas in wine. It also reduces acetic acid and acetaldehyde levels in wine when used in conjunction with Saccharomyces cerevisiae.

Question 21

Describe Brettanomyces

Answer 21

These yeast produce volatile phenols that may contribute smoky, medicinal, and barnyard aromas which are considered off-flavours to some winemakers.

Question 22

Describe Saccharomyces spp.

Answer 22

Saccharomyces cerevisiae is commonly found in vineyards around the world, as are a number of other Saccharomyces species. These yeasts are usually the main consumers of must sugars, and thus produce the bulk of the wine’s alcohol.

Question 23

Why might spontaneous fermentation might be used?

Answer 23

The interactions of these different organisms are thought to increase the complexity of flavour.

We do not have to go to the effort and expense of choosing and purchasing cultured yeast strains.

Some regions’ legislations may prohibit the addition of cultured yeasts. French calvados for example.

Some use spontaneous fermentation as a marketing tool.

Question 24

What are the several factors that causes a longer fermentation time?

Answer 24

A higher starting gravity means more sugars need to be fermented.
Lower pH levels can slow the fermentation.
Heating options may not be available during colder months.
There may be a nutrient deficiency that, due to local regulations, the distiller is not allowed to correct.
f the fruit has been washed before processing, and is undergoing spontaneous fermentation, the must may not contain many yeast cells. This causes a lengthy lag time before fermentation.

Question 25

What is Maolactic fermentation mostly due to?

Answer 25

Oenococcus oeni - Many strains of Lactobacillus and Pediococcus can also be involved.

Question 26

Describe Acetobacter

Answer 26

Bacteria Forms a film on top of wine exposed to the air Converts ethanol > acetic acid and ethyl acetate

Question 27

Describe Kloeckera apiculata

Answer 27

species of yeast naturally present on grapes If not controlled, can produce large amounts of ethyl acetate - solvent like aroma

Question 28

Describe Brettanomyces spp.

Answer 28

Generally not a problem for distillers, they take several months to produce unwelcome flavour compounds

Question 29

Describe Lactic acid bacteria

Answer 29

large group of bacteria. Harmful to wines: Pediococcus spp., Lactobacillus spp., and Lactococcus spp. can cause problems diacetyl production, and excessive ethyl acetate levels.