Alcoholic fermentation uses yeast to convert 1 sugar (C6H12O6) molecule into 2 ethanol (CH3CH2OH) and 2 carbon dioxide (CO2) molecules, giving off heat in the process.
Cultured yeast is almost always used in distillation. The sugars may come directly from grapes or sugar cane or be converted from grain or potato starch or agave inulin. Other alcohols are also produced such as methanol and fusel oils.
Name the 3 forms that plants store carbohydrates in
Sugars: soluable in water; grapes and sugar cane
Starch: must be converted to sugar; grains and potatoes
Inulin: must be converted to sugar; agave
What is distillation?
Boiling and condensing an alcoholic liquid to separate it into its constituent parts.
Name the 5 steps of spirits production
Selecting the raw material
Processing the raw material
Post-distillation operations (maturation, addition of flavor, blending, finishing)
Name the 2 outcomes of alcoholic fermentation
A minor chemical constituent that imparts distinctive character or is responsible for physiological effects
Name the 3 sources of congeners
Produced by yeast
Chemical reactions between congeners and/or alcohols
Name 4 groups of congeners
Constituent parts of an alcoholic liquid
What is the boiling point of ethanol?
Name 3 reasons why copper is important in spirits production
Easy to shape (stills have complex shapes)
Excellent conductor of heat
Reacts with sulfer compounds (removes them from final spirit)
As heat is lost, some vapors condense and fall back as liquid through rising vapors.
When vapors and liquid mix in a still they share heat.
The more volatile fractions become vapor and the less volatile liquid.
Thus, reflux increases the amount of separation between fractions.
More reflux results in more rectification and a more alcoholic product.
Progressive increase in the level of ethanol due to reflux
How many rectification plates are found in stills
3 to 42
Name 2 types of rectification plates
Bubble Cap: tray also includes weir and downcomer
Sieve: upward flow of vapor stops liquid from falling through small holes in tray
Name the 2 parts of a condenser
Tube(s) where spirit enters as a vapor and leaves as a liquid
Coolant, typically water
Name the 2 types of condensers
Worm tub: vapor passes through single coiled tube; oldest type but still popular
Shell and tube: vapor passes through many narrow vertical tubes
Name the 2 types of stills
Pot: boiling pot with connecting tube to a condenser
Column: usually round structures internally divided by 15-42 rectification plates
Where are pot stills used?
Name 2 disadvantages of using a pot still
Not possible to produce a highly rectified spirit needed to make vodka
Constantly needs to be filled, used, emptied, and cleaned
What is the linking tube to a condenser in a pot still known as?
Name the 5 elements of a pot still
Pot (where liquid is placed)
Head (where reflux takes place)
Name the 3 methods to heat pot stills
Direct heat: open flame, usually gas fuel; solids can get scorched
Steam: through inside coil or outside jacket; better control than direct heat but scorching remains a risk
Water bath: outside jacked filled with heated water; aka "bain marie" or "bagno maria"
Define batch distillation
liquid must undergo two or more separate distillation to produce final spirit
Name 4 factors that impact the amount of reflux in a pot still
Temperature: a gentler boil increases the temperature gradient, which increases reflux which limits passage of less volatile congeners
Height and shape of the head: greater the height the greater the reflux
Angle of the linking tube: reflux can continue in tube if angled up
Rectifying plates and head condensers: produces more highly rectified spirits; option to bypass
How long does each distillation in a pot still take?
How many distillations does it take to produce a spirit?
Usually two but sometimes three
What is the purpose of the first distillation in a pot still?
Separate the volatile and non-volatile (solids) fractions from the liquid
All the liquid that flows off the still is collected as one product
A watery waste product remains
It is NOT used for rectification or refining flavors
What is the purpose of the second distillation in a pot still?
Determines the style and flavor of the spirit by collecting three products
Heads: high concentration of methanol and can be tainted by residue in still head
Heart: used to make the final spirit
Tails: high concentration of fusel oils make any spirit unpalatable
Why are the heads and tails distilled with the next first distillation?
To recover the ethanol
Does the boiling point of the alcoholic liquid change during distillation?
Yes: it rises. As more ethanol than water vaporizes during distillation, the abv of the remaining liquid slowly drops and its boiling point rises.
What is a dephlegmator?
Head condenser (cold water is circulated through an enclosed section in the top of the still)
What types of still can perform batch distillation?
Column (e.g., small premium Vodka producers)
What types of still can perform continuous distillation?
Is batch or continuous distillation more efficient?
Continuous; but an enormous volume of alcoholic liquid is required to maintain constant flow
What is Highly Rectified Spirit (HRS)?
A spirit distilled to at least
EU: 96% abv
USA: 95% abv
Name 2 synonymns for Highly Rectified Spirit (HRS)
Grain Neutral Spirit (GNS)
It is NOT the same as vodka
What is the highest ratio of ethanol to water achievable through distillation?
97.17% ethanol by volume
95.57% ethanol by weight
Consistency: create a range of brands that taste the same batch after batch
Accessibility: easier on the palate
Affordability: blending may make a spirit cheaper
Commercial viability: sell small production
Name types of blending
Blended whiskies: mix of grain and malt whiskies
Malt whiskies: different distilleries, ages, casks
Rum: produced on different islands; "export in barrels" to UK
Gin: botanicals may be distilled separately
What is conversion?
The process whereby insoluble carbohydrates such as starch and inulin are converted to soluble sugars so that they can be fermented.
Examples: marlting barley, cooking (wheat, corn, agave) at high temperatures to hydrolyze starch, using enzymes to create sugar
Why are spirits blended?
Most aged spirits are blended to ensure brand consistency. The contents from many barrels are mixed in a vat and allowed to marry for a few months prior to sale. Most blenders use different ingredients produced by varying distillation and maturation practices. In Scotland, blending companies own several distilleries, each producing a unique product.
Why are spirits colored?
Once a spirit is ready for sale it is finished by diluting it with pure water, adjusting its color to ensure brand consistency with spirit caramel (which does not affect flavor), and filtering (to remove particles from the barrel surface to the spirit is clear and bright). Many other sources of color are used for flavored spirits and liqueurs.
Name 4 classes of caramel coloring and what they are used for
Class I E150a: high alcohol spirits like whisky; heated sugar
Class II E150b: Cognac, Sherry, brandy, tea; sulfite (SO3) compounds
Class III E150c: beer, soy sauce, confections; ammonium (NH4) compounds
Class IV E150d: high acid like colas; carbohydrates heated with sulfite and ammonium compounds
Name the elements of a column still
Ways of promoting reflux
Analyzer column ("stripper") for first distillation (separate volatile fractions)
Rectifier column for second distillation (rectify volatile fractions)
How many columns are in a column still?
Theoretically one: a rectifier on top of the analyzer
Double column: patented by Aeneas Coffey in 1830
Five column: Adds hydroselection and de-methylizer columns to remove flavors; also adds a second rectifier column to bring the low-strength output of hydroselection back up to 96% abv for input into the de-methylizer.
What does a hydroselection column do and how does it work?
Removes fusel oils
Dilute spirit to 20% abv (hot water from above and steam from below)
Fusel oils rise to top and diluted spirit collected at the bottom
What does a de-methylizer column do and how does it work?
Heat 96% ethanol spirit with a reboiler (since steam would dilute product)
Methanol rises to top and ethanol spirit collected at the bottom
Necessary for vodka production in the EU
Name 2 methods to heat the base of continuous stills
Direct injection of steam
What is a reboiler?
Steam-powered heat exchanger
Name 3 ways to promote reflux in a continuous still
Preheat alcoholic liquid as it passes in a tube between rectification plaates
Pour some spirit back into the still to promote downflow
Does every spirit undergo all post-distillation operations?
No: legal requirements and producer choices determine maturation, addition of flavors, blending, and finishing operations.
A post-distillation operation
Some spirits are sold unaged (stored in stainless-steel vessels)
Many spirits are matured in wood vessels, usually oak
Are all spirits colorless with water-white intensity when they come off the still?
What is oak used for?
Spirits that are matured most often use oak barrels. Oak imparts color and many positive flavors. Barrels can be formed into waterproof but not airtight containers and offer an ideal ratio of wood to liquid.
Name 8 factors that influence the flavors imparted by oak barrels:
Removing harsh flavors when congeners are absorbed by carbon or via evaporation
Adding congeners from the oak (e.g., aromas of vanilla, coconut, cloves)
liquid previously stored and absorbed in the barrel
Species of oak
Amount of blackening (toasting) or burning (charring) the inside of the barrel
The number of times the barrel has been used before
Fill strength (some congeners are soluable in water while others are soluable in ethanol)
Warehouse temperature, humidity, and positioning
How does temperature, humidity, and positioning affect maturation?
Warm-dry: more water evaporates so abv rises
Cool-damp: more ethanol evaporates so abv falls
High temp: flavor/color extracted from wood more rapidly (spirits mature in the Caribbean faster than in Scotland)
Warehouse positioning: affects temperature and humidity
Name 3 factors that determine the extent of flavors contributed by an oak species
How it was made
Age of the barrel
Name 3 important species of oak used to make barrels
Quercus alba: North America
Quercus robur: Europe
Quercus sessiliflora: Europe
Name 3 ways an oak barrel affects the flavor of a spirit
Subtract flavors: congeners are absorbed by carbon or through evaporation
Adds flavors from oak: vanillin (vanilla), lactones (coconut), eugenol (cloves)
Adds flavors from previous contents:
Congener reactions: congeners from oak and spirit react with each other or oxygen
Why are spirits diluted to 60%-70% abv before they go into barrel?
Higher abv would extract unpleasant flavors from the oak
Describe the skill of blending
Produce the same results from a changing palette of ingredients
Name the 3 steps of finishing?
Dilution ("breaking down"): in one go or in stages over time; result is 37%-43% abv
Coloring: adjusted due to barrel variation; does not affect flavor
Filtration: consumers prefer clear and bright spirits; required for mature spirits to remove barrel particles; chill-filtration controversial; charcoal filtration can remove color as well as flavor
What is "chill-filtraton"?
Spirit chilled to form haze so it can be removed by filtration