Alcoholic Fermentation

Question 1

What is alcoholic Fermentation?

Answer 1

Heat and yeast convert sugar to alcohol and CO2 in absence of O2

Question 2

What is yeast?

Answer 2

Microscopic fungi that converts sugar into alcohol
-affects aroma and flavour characteristics

Question 3

What do yeast need initially and why?

Answer 3

-oxygen- to multiply quickly
-once ox been used up- switch to ferm (aerobic respiration)

Question 4

What does yeast need?

Answer 4

-access to nutrients (nitrogen)
-viable temp range
-absence of ox

Question 5

As well as heat, alcohol, Co2, what else does yeast produce?

Answer 5

-volatile acidity
-wine aromatics
eg aroma precursors (eg thiols)
eg created by yeast (eg esters- banana and sometimes undesirable reductive flavours)
-v small amount of naturally produced CO2
-gycerol

Question 6

What is the most common strain of yeast used and why?

Answer 6

-saccharomyces cerevisiae
-resistant of so2
-can withstand high acidity and increasing alc level- ferments fully to dryness

Question 7

What is ambient yeast?

Answer 7

-‘wild yeast’ found in vy and winery
-includes kloeckera and candida
-saccharomyces cerevisiae dominant yeast

Question 8

What are the advantages of ambient yeasts?

Answer 8

-complexity from diff variations of yeast used and aromas
-free to use
-unique to place or region
-marketing

Question 9

What are the disadvantages of ambient yeasts?

Answer 9

-slower to start ferm- risk of spoilage organisms and VA
-not consistent
-ferm to dryness takes longer= not desirable in high vol winery
-increased risk of stuck ferm

Question 10

What is cultured yeast?

Answer 10

-selected in lab, then grown in vols suitable for sale
-often single strains of saccharomyces cerevisiae

Question 11

How to use cultured yeasts?

Answer 11

-must cooled down to avoid ferm by ambient yeast
-can also add so2 to avoid ^
-then cultured yeast added=overwhelms natural yeast population
-starter batch of fermenting grape must been activated with cultured yeast added to tank of must to be fermented

Question 12

What are the advantages of cultured yeast?

Answer 12

-quick and reliable ferment to dryness
-consistent
-less risk of microbial spoilage, low VA
-large selection of cultured yeasts, WM can choose for style of wine. eg can use one strain to boost aromatics in savy b
-or a neutral one for sparkling wine

Question 13

What are the disadvantages of cultured yeast?

Answer 13

-cost of commercial product
-similarity of fruit expressions

Question 14

What is the temperature for cool wines?

Answer 14

12-16 degrees
-fresh fruity whites and roses
-promotes production and retention of esters- fruity aromas and flavours

Question 15

What is the temperature for med temp ferm?

Answer 15

17-25
-easy drinking reds, low tannins extraction

Question 16

What is the temperature for a warm ferment?

Answer 16

26-32
-max extraction of colour and tannin but can result in loss of some fruit flavours

Question 17

What is MLF?

Answer 17

Malic acid-lactic acid using lactic acid bacteria

Question 18

What encourages MLF?

Answer 18

-16-22 degrees
-Mod PH (3.3-3.5)
-Low total SO2
-can also be started by ‘inoculating’ w cultured lactic acid bacteria

Question 19

What prevents MLF?

Answer 19

-temp below 15 degrees
-low PH
-adding SO2
-lactic acid bacteria can be filtered out to avoid mlf

Question 20

What are the outcomes in the wine from mlf?

Answer 20

-lower acidity, higher PH (lactic acid weaker than malic
-smoother, softer style
-new aromas, buttery
-microbial stability
-loss of colour

Question 21

Why might some people want to do mlf in barrels instead of tanks?

Answer 21

-can stir in the lees at same time
-promote better integration of flavour

Question 22

Why might some people prefer to do mlf at same time as ferm?

Answer 22

-increase fruity characteristics
-shorter production time