Unit 5 Flashcards
Define maturation
The sum of the chemical and physical changes that occur within the spirit between distillation and bottling.
Which congeners typically decrease during maturation?
Ethanol
Lower boiling point aldehydes
What congeners typically increase during maturation?
Esters
Acids
What congeners are introduced from the barrel during maturation?
Non-volatile compounds- sugars and tannins.
4 classes of change during maturation
Additive
Productive
Reductive
Subtractive
Additive changes during maturation
Compounds gained from the casks, usually tannins, sugars, aromatic aldehydes, and lactones.
Main type of tannins found in oak
gallic acid base
Ellagitannins.
What is a tannin
phenolic compound gives astringent character, removes off-notes, and promotes oxidation products.
How to tannin levels change during maturation?
Rise early, then decrease (after 5 years)
Hydrolyse to give usually glucose, and phenolic acid
Organic acid activity during maturation
Usually acetic acid, increases during maturation, as it is extracted from wood.
Leads to increased ester production
2 whisky lactones
cis-β-methyl-γ-octalactone and trans-β-methyl-γ-octalactone
Coconut, sweet wood, and vanilla at low sensory thresholds
Lactones during maturation
Increase
Carbohydrates during maturation
Increase, directly from the hemicellulose of the wooden casks, and also from hydrolysing tannins.
Improve sweetness and positively affect mouthfeel
Increase colour (hemicellulose)
Lignin activity during maturation
Increases in the spirit from the cask, dependent on the level of cask charring.
Increase colour & blend complexity.
Production on vanilla and oxidation products.
Hydrolysed, then oxidised, then esterification.
What is lignin?
Structural polymer found in oak
Phenolic aldehydes formed from heat degrading lignin?
Coniferaldehyde (bready)
Vanillin (vanilla)
Syringaldehyde (spicy/woody)
Toasting temperature for max phenolic aldehydes?
200 degrees (degraded when charred above 250, as most American casks)
Productive changes during maturation
Add flavours and aromas from with compounds within the spirit.
Ester formation
How is an ester formed?
Reaction between an alcohol and an organic acid.
(hydrolysation of lignin, then oxidation, then esterification)
Most common ester found in spirits?
Ethyl acetate
fruity, solvent like aroma
How does the charr layer contribute to flavour?
Burnt wood
removes off notes (rubber)
Reductive changes during maturation
Less desirable compounds are converted to something less aromatic or flavoured.
2 examples of reductive changes during maturation
Acetaldehyde (green apples) oxidised to acetic acid
Acrolein (LAB or glycerol = acrid/peppery) oxidised to acrylic acid
Subtractive changes during maturation
Total removal of compounds through evaporation or adsorption.
2 examples for subtractive changes during maturation
Evaporation of acetaldehyde (low boiling point)
DMS (Di-methyl sulphide) dissipates from spirit into the air, there is also adsorption into the char layer.
Main countries supplying oak for casks
USA & France
Spain, Portugal, then Eastern Europe.
Characteristics of Quercus alba
American Oak
- Fine, tight, uneven grain.
- 100-120 y/o
- Rich in vanillin, lactones, coconut, woody (less tannins than European oaks)
- Abundant tyloses
Characteristics of Quercus petraea
European oak sp.
-Medium large pores, coarse to tight grain.
- 300 y/o
- Troncais and Jupilles (France)
- Rich in lactones, coconut and woody.
Characteristics of Quercus robur
European Oak sp.
- Wide, straight grain, coarse uneven texture.
- 150-200 years.
- Limousin (France)
- Ellagitannins produce cooked apple character, rich tannins increase smoothness.
Oak Properties
Cellulose
Organic compound, forms plant cell walls.
Gives barrels strength, but does not affect flavour.
Oak Properties
Hemi-cellulose
Short glucose polymer
20-25% of oak matrix
Easily hydrolysed into sugars.
Oak Properties
Lignin
20-25% of oak matrix
Undergoes thermal degradation during seasoning and toasting, producing key flavour compounds extracted during ethanolysis.
Oak Properties
Hydrolysable tannins
Astringency
Gallic and Ellagic acid into spirit.
Too much - over oaked
2 main ellagitannin isomers found in European oak?
Vescalagin
Castalagin
Volatile compounds in oak & flavours
Oak lactones cis (coconut) and trans (spicy)
Vanillin
Eugenol (cloves, allspice)
Guaiacol and 4-methylguaiacol (smokey, tobacco)
Furfural and 5-methylfurfural (aroma butterscotch, caramel, almonds)
Volatile compounds which reduce with more toasting
Vanillin (inc, then decrease)
Cis and Trans lactones
Volatile compounds which increase/are generated by more toasting
Guaiacol and 4-methyl guaiacol
Furfural and 5-methylfurfural
Eugenol
Coarse grain properties
<2 rings/cm
More fibre = more lignins = more tannins.
Ellagitannins = mouthfeel.
Less porous.
Q. robus (limousin)
Fine grain oak properties
5+ rings/cm
Less fibre = more vessels = more nutrient, sugars, etc.
More porous.
Aromatic, lactones, eugenol.
Q. alba.
Describe natural cask seasoning
- Staves stacked into ricks with good air flow.
- Leave for 18-36 months
- Expose to sun and rain first 8-10 months to leave green tannins.
- Dry to 12-24% moisture.
- Fungal colonies develop which can break down cellulose and tannins.
- Dimensions retract.
- Preferable, increases aromatic compounds (vanillin, eugenol, syringic)
Cis lactone is higher in natural seasoning.
Describe forced drying.
Kiln for 1 month
More astringency, as no leaching through sun and rainwater of ellagitannins.
Define a light toast
5 minutes.
Internal surface is 120-180°C
Modified lignin and hemi-cellulose
Intact cellulose
Define a medium toast
200°C for 10 minutes.
Hemi-cellulose and lignin disappear.
Define a heavy toast
230°C held for 15 minutes.
Internal structure is blistered and cracked.
Which aromatic compounds are found in the largest amounts in medium toast?
Volatile phenols (guaiacol, eugenol)
Volatile aldehydes (vanillin)
Which aromatic compounds are found the in largest amounts in light toast?
Ellagitannins (gallic, ellagic acid)
Which aromatic compounds are found in the largest amount in heavy toast?
Cis and trans lactones.
Reasons for charring
American oak - regulation
Scotch - regeneration
Increases surface area and gives active charcoal for sulphur adsorbtion.
Increases lignin aromatic compounds (spice/smoke)
Breaks down hemi-cellulose and cellulose = vanillin.
Char level 1
15 seconds
wood character and campfire aromas
Char level 2
30 seconds
caramel, vanilla, coffee
Char level 3
35 seconds
earthy spice, wood scent, smoke, deep colour.
Char level 4
55 seconds
aka alligator skin
smoke, tobacco, heavy spice, cloves, sweet caramel notes.
6 types of cask
American standard barrel
Hogshead
Butt
Puncheon
Barrique
Charred new barrels.
American standard barrel
190-200L
SAVR - 100cm2/L
American white oak
Vanilla & caramel
Hogshead
225-250L
SAVR - 88.5cm2/L
Assembled from American white oak ex-bourbon staves.
Butt
450-500L
SAVR - 71cm2/L
Often used for sherry.
Traditionally Spanish oak
Puncheon
450-500L
SAVR - 67.5cm2/L
Most common for sherry.
Fatter than a butt and made from Spanish oak staves.
Highly prized
Barrique
225L
Wine, European or American oak.
Charred new barrels
190-200L ASB
Used for bourbon.
3 main cask ‘type’ categories
Virgin
First fill
Refill
Virgin casks
Usually American heavy (3-4) char
High extraction (fast but intense)
Good physical shape, but expensive.
Primarily bourbon, but also cognac.
First fill
Primary whisky maturation (first re-fill)
Attention paid to previous fill (wine - sulphur)
1/3 price of virgin casks
lower extraction
Refill casks
Refilled by the distillery with their same spirit.
Oxygenation still occurs, even if cask is exhausted for extraction.
Oxidation, evaporation (congeners, alcohol)
Concerns - leaking, rusting, extraction.
Cons of smaller casks
expense
space
higher evaporation losses
productive and reactive reactions are not increased by surface area to volume ratio.
Therefore - hot/astringent/immature spirit character.
Typical Scotch filling ABV
63-64%
Water soluble compounds
Glycerol, tannins, sugars
Alcohol soluble compounds
lactones (cis and trans)
Higher barrel fill strength =?
Lactone extraction
Lower colour extraction
Lower volatile acids
Overall slower uptake of maturation character
Lower barrel fill strength =?
Extraction of wood sugars and tannins.
More colour extraction.
More volatile acids.
What is saponification?
Fatty acid reacting with a base to create a salt of the fatty acid. (heat speeds up this reaction)
How do higher temperatures affect maturation?
Faster extractions and chemical reactions (some)
Oxygen less dissolvable, however increased evaporation = more head space for air/liquid interaction.
Losses 4-10% per year.
How does humidity affect maturation?
High humidity = more alcohol evaporation
Low humidity = more water evaporation.
Factors affecting warehouse matuaration
Temperature
Humidity
Type and nature of construction materials
Maturation conditions in Scotland
Low temp and high humidity, 2% alcohol loss per year.
Long times
3 types of warehouse organisation
Rick
Dunnage
Palletised
Rick warehouses
7-9 stories of wooden shelves with casks rolled on.
20 000 casks
55% on level 1 to 72.5% on level 9
hot and dry at the top
cool and humid at the bottom
different maturation at different points.
Dunnage warehouse
long rows of 2-3 barrels high.
less space efficient
earth floors to increase humidity and consistent temperature.
Pallet warehouse
Good for space and easy to move with machinery.
Some concerns regarding airflow.
Solera systems
Higher, younger barrels top up lower older barrels.
Consistency of spirit produced.
Effects of oxygen during maturation
- polymerise tannins = soften astringency.
- Helps form aromatic compounds from lignin degradation by-products
- Oxidise hydrogen sulphide
- Oxidises compounds into carboxylic acids which combine with alcohol to form esters.
