7.4: Alcohol and Spirits
Alcohol and Spirits
Proof VS % Volume
This link provides some insight into the difference between proof and ABV (Alcohol-by-volume).
Beer Production
Beer has been produced by humans for 6000 to 8000 years. The key ingredients are a malted barley, water, hops, and yeast.
Typical Steps in Beer Production:
Barley
Barley is a widely adaptable and hardy crop that can be produced in temperate and tropical areas. Barley kernels or grains are the fruit of the barley grass. The endosperm contains many starches as a food reserve for the baby plant. The starch and the embryo are surrounded by the husk, a protective layer around the kernel. While people have made beers from other grains, many people define beer as the fermented alcoholic barley drink. In fact, the German beer purity law, known as the Reinheitsgebot , of 1516 allows for only hops, barley, water and yeast in the production of beer.
Step 1: Malting the Barley
The goal of the first stage of beer making, malting the barley, is to access the fermentable carbohydrates.The barley grains are soaked, called steeping . This process triggers metabolism in the grain to start germination for 4-5 days. As the baby plant starts to grow, the enzymes begin to break down the starches and the cell wall.The cell wall surrounding the starch containing endosperm is primarily made of beta-glucan and pentosan. Beta-glucan and pentosan are structural polysaccharides athat are not digestible by humans or yeast enzymes (i.e. fiber). To stop germination and enzymatic processes, that grain is heated, called kilning .
Kiln Variations
There are many varieties of kilned malts . These are a few of the popular styles:
- Pale malt : low and slow kilning at around 100 F and 120 F for as long as 24 hours. This yields a pale beer.
- Vienna malt : kilned at a relatively low temperature, though it can be heated as high as 160 F. It is known for its toast or biscuit like flavor and the pleasant orange color.
- Munich malt : kilned at a high temperature, between 195 F and 220 F. It has a sweet, bready flavor and imparts a nice amber color.
- Aromatic malt : kilned at a high temperature, between 195 F and 220 F. It is sweet and gives the beer a malty, almost syrupy flavor and aroma.
Roasting the malts promotes Maillard reactions This leads to the complex flavors promoted during this stage.After kilning, the malt grain is then cleaned, transported, and stored. Most breweries purchase their malts rather than prepare them.A diastatic malt has enough enzymes (such as amylase) to convert the starch into fermentable sugars in the mashing stage.
Step 2: Brewing
Brewing involves multiples steps. Here is an overview.
- Mill : grinding the malt into a flour called grist
- Mash : mixing the grist with heated water to allow water and enzymes to hydrolyze the starch to form the ‘ wort ’, a sugary liquid
- Wort Separation : filtering the wort from the insoluble husk particles and other grain particles. Traditional practices used the husk as the filter; modern breweries use polypropylene filters
- Boiling : hops are added to the wort and the mixture is boiled.
- Clarification : denatured proteins, tannins, and hop remains are removed
There is some important chemistry occurring in these steps. We will look at some of the enzymes, the hops, and the boiling steps in more detail.
Mill:
In this step, the grains are broken up in a mill. The particle size, grist , can be determined by the spacing on the rotors.A large grist was traditionally favored because the crushed grain was used for the filtering at the end of the brewing process.Modern brewers use small grist because they use polypropylene filters.
Mashing: Enzymes
Mashing is the brewer's term for the hot water steeping process which hydrates the barley, activates the malt enzymes, and converts the grain starches into fermentable sugars. Typically, hot water is added to help solubilize starches.
Mashing: Hops
Hops are a climbing perennial vine and the cone of the flower is used to add ‘bittering’ and aroma flavors to the beer wort during this phase of beer production. Typically, these cones are milled and pressed into pellets for use by the brewer. Other brewers use extracts of the cones.
Tannins are astringent polyphenolic compounds that are widely distributed in many species of plants, where they play a role in protecting the plants from predators. The astringent flavor predominates in unripe fruit, red wind or tea.
Hops added after boiling is called ‘dry hopping’. Hop oils (essential oil) are sometimes added after boiling of the wort. These ‘aroma hops’ are volatile non-polar compounds that have strong aromas and flavors. There are between 400 and 1000 different compounds in hop oil including structures such as myrcene, humulene, carophyllene, beta-pinene, geraniol, linalool, and farnesene.
Brewing: Adjuncts
Liquid adjuncts (sugars/syrups) are usually added in the wort boiling stage. They may be sugars extracted from plants rich in fermentable sugars, notably sucrose from cane or beet or corn syrup. Liquid adjuncts are frequently called “ wort extenders ”. The beer is then clarified.
Step 3: Fermentation
There are hundreds of strains of yeast. Many beer yeasts are classified as "top-fermenting" type ( Saccharomyces cerevisiae ) and or "bottom-fermenting" ( Saccharomyces uvarum , formerly known as Saccharomyces carlsbergensis ). Today, as a result of recent reclassification, both yeast types are considered to be strains of S. cerevisiae .
Wild Yeast
Beer that is brewed from natural/wild yeast and bacteria are called spontaneous fermented beers. One of the typical yeasts is the Brettanomyces lambicus strain which is used to produce traditional lambic beers. This brewing method has been practiced for decades in the West Flanders region of Belgium. We will visit 3 Fonteinen Brewery in Belgium thatspecializes in lambic beers.
Beer Types
Beer style is a term used to differentiate and categorize beers by various factors, including appearance, flavor, ingredients, production method, history, or origin. There is no agreed upon method for distinguishing beer styles.
There are some general categories that are used in describing beer styles:
Yeasts: Ales vs Lagers
- Ale: Top-fermenting strains that tend to produce more esters.
- Lager: Bottom-fermenting strains that tend to produce more sulfur compounds.
- Weizen Yeast: Used in German-style wheat beers and is considered an ale yeast.
- Brettanomyces: Wild yeast with flavors like barnyard, tropical fruit, and more.
Carbonation Level:
- Carbonation is a main ingredient in beer. Carbonation can be detected as an aroma (carbonic acid) and it has a mouth feel and flavor. It also affects the foam.
- Carbonation can be naturally occurring (produced by yeast during fermentation) or added to beer under pressure. N2 can also be added to beer, providing smaller bubbles and a softer mouth feel than CO2.
Craft Beer.com provides a nice style guide on the different names of beers with information about the yeast strains, hop aroma, IBU (International Bitterness Units), alcohol content, carbonation for hundreds of beer styles.
- Craft Beer.com Beer Style Study Guide
John Palmer also provides a nice table that places a wide range of beer styles on a chart comparing a number of ales and lagers on malty vs fruity and sweet vs bitter.
- John Palmer, How to Brew, Chapter 19, A Question of Style, Ales vs Lagers .
Alcohol itself does not contribute to the flavor of foods; only the main flavor component of the liquors or liqueurs does. Care should be taken to evaporate the alcohol fully or it may leave a bitter aftertaste in the dish.
Wine Production
Overview
Wine is defined as the fermented juice of a fruit. Wines have been produced from all kinds of plant materials and fruits. However, the most classic version is made from grapes.
Typical Steps in Wine Production:
Grape Preparation
The grape pulp has a high concentration of fermentable sugars while the skin and seeds have a lot of flavorful compounds.
Grapes: Varietals
The grape is the fruit of the vine, Vitis vinifera (wine) and Vitis labrusca (table grapes). There are over 5000 varietals of grapes which all have different flavor and aroma profiles.
A list of varietals (and pronunciations) is available from J. Henderson, Santa Rosa Junior College. The Wine Spectator has an article by J. Laube and J. Molesworth on Varietal Characteristics .
In Europe, wines are usually categorized by their geographic region. In America, Australia, South Africa and New Zealand, wines are usually labelled by their varietal names. The grapes will develop a different profiles of flavor chemicals depending on soil, temperature, growing practices, rain, etc. The land and climate are referred to as the ‘terroir’.
Chemical Components of Grapes
Polyphenols: Overall class of compounds
Polyphenols are a class of molecules characterized by the presence of large multiples of phenol structural units. This is a huge class of molecules found many plants. Grapes have a wide variety of polyphenols, most of which are concentrated in the skin and seeds. The concentration and types of polyphenols varies between grapes based on cultivar, 'terroir' – grape growing region (altitude, geological features, soil type, sunlight exposure), temperature during ripening, and environmental stressors such as heat, drought and light intensity. There are many sub-categories of polyphenols. Here is a simplified outline.
The flavor and appearance of red wines are determined by the phenolic compounds: anthocyanins (responsible for the red color) and tannins (responsible for the sensation of
astringency). Hydroxycinnamic Acids are mostly found in the grape pulp. Hydroxycinnamic acids are often found as esters of tartaric acid or with a sugar. During the processing, these esters are hydrolyzed. Stilbenes have two aromatic rings connected with an alkene (cis or trans). Resveratrol is one of the most common stilbenes found in grapes and wine. It is usually located in the grape skin. Flavones, Flavanones, and Flavonols are mostly found in the seeds and skin. Many of these flavonoids are present in the grapes as the glycosides (the sugar moiety can vary) but are cleaved in the processing to wine. Anthocyanins are also prevalent in wines and grapes. They are usually glycosylated. They are partially responsible for the color of grapes and wines.
Grape Processing
Stemming and Crushing
Harvesting of grapes is usually done in late summer and early fall. Harvesting for most large industrial wineries is mostly mechanical. The stems must be removed first to avoid ‘off-flavors’. The grapes are crushed immediately after picking. The goal of crushing is to release the sugars, acids and some of the polyphenols from the skins. For white wines, the juice is separated from the skins so that the color and tannins are not extracted into the must. For red wines, the juice and skin are both fermented. The grape skin cell walls are composed of polysaccharides (pectins, hemicellulose and cellulose) that prevent the diffusion of polyphenols into the must. Excessive crushing can release too many polyphenols.
Maceration
During winemaking, phenolic compounds are extracted into the juice by diffusion. A diffusion period, ‘ maceration ’, can be done as a cold soak, through heating, enzymes, or a variety of techniques intended to increase polyphenol extraction. Maceration can be before, during, or after fermentation. Maceration enzymes (pectinases and cellulases) are ofteh added during this process.
Polyphenols: Oxidation Reactions
Polyphenols are susceptible to oxidation with Fe and O 2 in solution or through the action of some yeast enzymes. This oxidation is called browning because the quinones are a brown, muddy color. Winemakers will usually add SO 2 to correct for the oxidation processes. Sulfite also prevents ethanol oxidation. It is important to remember that sulfite has another role; it can slow or prevent growth of spoilage organisms.
Adjusting Sugar Content in the Must
Sugar content is important as it effects the alcohol level of the final wine as well as the sweetness of the wine. ‘ Degrees Brix ’ is a density measurement that represents the sugar concentration in wine. 1 degree Brix (°B) = (% by weight) = 1 gram of sugar per 100 grams solution (water & sugar combined). Sucrose and/or grape juice can be added to the grape must.
Fermentation
Fermentation of the ‘grape must’ is an alcoholic fermentation by yeasts. Wine-makers can utilize wild fermentation or inoculation with a specific yeast strains of Saccharomyces cerevisiae . In spontaneous wine fermentation, the fermentation begins with non- Saccharomyces yeasts until the ethanol concentration reaches 3–4%. As the alcohol concentration increases, these yeasts die off, and Saccharomyces dominates the fermentation process. In inoculated ferments, S. cerevisiae is used to begin the fermentation process and its primary role is to catalyze the rapid, complete and efficient conversion of grape sugars to ethanol.
A good wine will have the components of alcohol, acidity, sweetness, fruitiness and tannin structure complement each other so that
no single flavor overwhelms the others. Recently, there has been a demand for a ‘richer’ red wine flavor; this has led winemakers to harvest grapes at a later stage to obtain more polyphenols and flavors. However, more mature grapes have increased sugar concentration.
Aging
The wine aging has two phases:
1) ‘maturation’, changes after fermentation and before
2) ‘bottling’. During the aging process, changes in taste and flavor occur.
Traditional maturation involves the storage of wine in barrels for a few months to a few years (or even longer!). During this time, the wine undergoes reactions and absorbs compounds from the wood of the barrels.
Processing: Clarification & Filtration of Wine
As a wine ages, phenolic molecules combine to form tannin polymers that fall to the bottom of the bottle. Unlike beer and cider, filtration is not a common process for wines so many older wines will have sediment. Many winemakers leave the sediments in the wine bottle. Wine drinkers can ‘decant’ the wine before drinking – pour off the wine leaving behind the sediment. Fining is a technique that is used to remove unwanted juice/wine components that affect flavor and aroma.
Filtration
Filtration is sometimes used to help control both MLF and Acetic Acid bacteria and other spoilage organisms since lees are a food source for the bacteria. LAB can continue the fermentation leading to off-flavors. Membrane filtration can be helpful at this point to remove organisms.
Sweetness/Dry
A dry wine has little residual sugars, so it isn't sweet. Sugars are the main source of perceived sweetness in wine, and they come in many forms. While it seems paradoxical, many people have noticed that wines with higher sugar content last longer even when open to the air. Osmotic pressure seems to play a part: high concentrations of sugar force the water within a microbe to rush outward, and its cell walls collapse.
Spoilage: Acetic acid
Acetic acid is responsible for the sour taste of vinegar. During fermentation, activity by yeast cells naturally produces a small amount of acetic acid. If the wine is exposed to oxygen, Acetobacter bacteria will convert the ethanol into acetic acid and is considered a fault.
Metabolism
Ethanol is passively absorbed by simple diffusion into the enterocyte. Ethanol metabolism occurs primarily in the liver, but 10-30% is estimated to occur in the stomach. For the average person, the liver can metabolize the amount of ethanol in one drink (1/2 ounce) per hour. There are three ways that alcohol is metabolized in the body.
- Catalase - an enzyme that we will cover again in the antioxidants section. Catalase is estimated to metabolize less than 2% of ethanol, so it is not in the figure below or discussed further.
- Alcohol dehydrogenase ADH - This is the major ethanol-metabolizing enzyme that converts ethanol and NAD to acetaldehyde and NADH, respectively. Aldehyde dehydrogenase ALDH uses NAD, CoA, and acetaldehyde to create acetyl-CoA and to produce another NADH. The action of ADH is shown in the figure below.
- Microsomal ethanol oxidizing system (MEOS) - When a person consumes a large amount of alcohol the MEOS, is the overflow pathway, which also metabolizes ethanol to acetaldehyde. It is estimated that the MEOS metabolizes 20% of ethanol, and it differs from ADH in that it uses ATP to convert reduced nicotinamide adenine dinucleotide phosphate NADPH + H+ to NADP+. The action of the MEOS is shown in the figure above.
At high intakes or with repeated exposure, there is increased synthesis of MEOS enzymes resulting in more efficient metabolism, also known as increased tolerance. ADH levels do not increase based on alcohol exposure. MEOS also metabolizes a variety of other compounds (drugs, fatty acids, steroids) and alcohol competes for the enzyme's action. This can cause the metabolism of drugs to slow and potentially reach harmful levels in the body3.
Females have lower stomach ADH activity and body H2O concentrations. As a result, a larger proportion of ethanol reaches circulation, thus, in general, females have a lower tolerance for alcohol. About 50% of Taiwanese, Han Chinese, and Japanese populations have polymorphisms in ALDH which cause the enzyme to have low activity. This leads to acetaldehyde buildup and undesirable symptoms such as: flushing, dizziness, nausea, and headaches.
Sources
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Casassa, Flavonoid Phenolics in Red Winemaking In Grapes and Wine, A. M. Jordão, Ed., 2018, InTechOpen.
Chantal Ghanam, Study of the Impact of Oenological Processes on the Phenolic Composition of Wines, Thesis, Université de Toulouse.
Dangles & Fenger, The Chemical Reactivity of Anthocyanins, Molecules, 2018, 23(8), 1970-1993.
Danilewicz, Role of Tartaric and Malic Acids in Wine Oxidation, J. Agric. Food Chem. 2014, 62, 22, 5149-5155.
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E.J. Bartowsky, Bacterial Spoilage of Wine, Letters in Applied Microbiology, 2009, 48, 149–156.
Garrido & Borges, Wine and Grape Polyphenols, Food Research International, 2013, 54, 1844–1858
Goold, et. al. Yeast's balancing act between ethanol and glycerol production in low-alcohol wines, Microbial Biotechnology 2017, 10(2), 1-15.
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J. Harbertson, A Guide to the Fining of Wine, Washington State University
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