Food Fermentation: Microbes and Food Products

Introduction

Milk and milk products: Acidophilus Milk, Cultured Buttermilk, Yoghurt, Sour cream, Kefir, Koumiss, Villi & Cheeses

Plant based products : Soy Sauce, Miso, Tempeh

Fish products: Paste & Dried

Meat products: Salami, Sausage etc.

Vegetables: Sauerkraut, Kimchi, Olives, & Cucumbers

Beverages: Beer, Ales, Wine, Whiskeys, Vodka, Gin & Rum

Fermented Milks

At least 400 different fermented milks are produced. These fermentations are carried out bymesophilic, thermophilic, and probiotic lactic acid bacteria, as well as by yeasts and molds

Lactic Acid Bacteria

The majority of fermented milk products rely on lactic acid bacteria (LAB).

LAB include species belonging to the genera Lactobacillus, Lactococcus, Leuconostoc,and Streptococcus

These bacteria are low GC gram-positives that tolerate acidic conditions, are nonsporing,and are aerotolerant with a strictly fermentative metabolism.

Mesophilic milk fermentations result from similar manufacturing techniques, in which acid producedthrough microbial activity causes protein denaturation (approximately 20 to 30°C and stops microbialgrowth by cooling).

Acidophilus milk is produced by using Lactobacillus acidophilus.

Lactobacillus spp. and Lactococcus lactis cultures are used for aroma and acid production.

The organism Lactococcus lactis subsp. diacetilactis converts milk citrate to diacetyl, which gives abuttery flavor to the finished product.

The use of these microorganisms with skim milk produces cultured buttermilk, and when cream is used,sour cream is the result.

the fermentation takes longer than for yoghurt and great care must be taken to avoid contamination

Lb. acidophilus cells do not survive well in the acid product, dying out after about a week's storage at 50C.

It often is used as a dietary adjunct, especially for lactose intolerant persons

Many microorganisms in fermented dairy products stabilize the bowel microflora, and some appear tohave antimicrobial properties.

Benefits of consuming fermented milks may involve minimizing lactose intolerance, lowering serumcholesterol, and possibly exhibiting anticancer activity.

MesophilicAcidophilus milk

Another interesting group used in milk fermentations are the bifidobacteria. Thegenus Bifidobacterium contains irregular, nonsporing, gram-positive rods that may beclub-shaped or forked at the end.

Bifidobacteria are nonmotile, anaerobic, and ferment lactose and other sugars toacetic and lactic acids. They are typical residents of the human intestinal tract and manybeneficial properties are attributed to them

Some believe that they promote calcium absorption and the synthesis of B-complexvitamins.

Bifidobacterium-amended fermented milk products, including yogurt, are nowavailable

Cultured buttermilk: Mesophilicfermented of pasteurized milk having 1–2% Fat with ~10 days fermentationmaximum

LAB: Lactococcus lactis (Lactococcuslactis subsp. lactis*, Lactococcus lactissubsp. cremoris, Lactococcus lactis biovar.diacetylactis and Leuconostocmesenteroides subsp. Cremoris)

Thermophilic fermentations can be carried out at temperatures around 45°C.

An important example is yogurt production. it is one of the most popular fermented milk products in the UnitedStates.

In commercial production, nonfat or low-fat milk is pasteurized (milk is heated at 80-90 0C for about 30 min),cooled to 43°C or lower, and inoculated with a 1:1 ratio of Streptococcus thermophilus and Lactobacillusdelbrueckii subspecies bulgaricus (L. bulgaricus).

S. thermophilus grows more rapidly at first and renders the milk anaerobic and weakly acidic.

L. bulgaricus then acidifies the milk even more.

Acting together, the two species ferment almost all of the lactose to lactic acid and flavor the yogurt withdiacetyl (S. thermophilus) and acetaldehyde (L. bulgaricus).

Both will grow on their own in milk but will grow and acidify the product faster when present together.

Acetaldehyde (ethanal) is the most important flavour volatile {(23-41 mg/kg (pH 4.2-4.4)}

Because of its high acidity and low pH (usually 3.8-4.2), yoghurt is an inhospitable medium for pathogens

Satisfactory yoghurts should contain more than l08 cfu/g of the starter organisms,

Yoghurt is not usually pasteurized since chill storage will arrest the growth of the starter organisms.

Fruits or fruit flavors to be added are pasteurized separately and then combined with the yogurt. Freshlyprepared yogurt contains about 109 bacteria per gram.

ThermophilicYoghurt

Microorganisms such as Lactobacillus and Bifidobacterium are being used in the rapidly developing area of probiotics

Benefits: Immunomodulation, control of diarrhea, anticancer effects, and possible improvement of Crohn’s disease (inflammatory bowel disease)

Yoghurts are spoiled by acidoduric organisms such as yeasts and moulds.

Yeasts such as the lactose-fermenting Kluyveromyces fragilis and, in fruit-containing yoghurts, Saccharomyces cerevisiae are particularly important

The yeast-like fungus Geotrichum and surface growth of moulds such as Mucor, Rhizopus, Aspergillus, Penicillium, and Alternaria can also be a problem.

Sour cream

Yeast-Lactic Fermentation

Kefir and koumiss are distinctive fermented milks produced by a mixed lactic acidbacterial fermentation and an alcoholic yeast fermentation.

Popular in Russia and those states which comprised the old Soviet Union

Yeast-lactic fermentations include kefir, a product with an ethanol concentration of upto 2%.

This unique fermented milk originated in the Caucasus Mountains and it is produced eastinto Mongolia.

Kefir products tend to be foamy and frothy, due to active carbon dioxide production.

This process is based on the use of kefir “grains” as an inoculum. These are coagulatedlumps of casein that contain yeasts, lactic acid bacteria, and acetic acid bacteria.

In this fermentation, the grains are used to inoculate the fresh milk and then recovered atthe end of the fermentation.

kefir

Composed largely of a strong polysaccharide material, kefiran,

Fresh milk could be added occasionally to maintain activity.

Several yeasts have been reported including Candida kefir, Saccharomyces cerevisiae andSacc. exiguus.

Sacc. exiguus is particularly interesting because it was shown to utilize galactosepreferentially in the presence of glucose and this may confer an advantage when growing ina mixed culture of organisms most of which will preferentially metabolize the glucoseportion of lactose

Milk for kefir production is homogenized and heated to 85-95 0C for between 3 and 10min. It is cooled to 22 0C before addition of kefir grains at a level of up to 5%.

The fermentation itself lasts for 8-12 h but is sometimes followed by slow cooling toaround 8 0C over 10-12 h to allow for the required flavour development

Kefir has an acidity of about 0.8%

Ethanol, lactic acid and carbon dioxide, acetaldehyde (ethanal) and diacetyl are alsopresent as flavour components.

Koumiss is a fizzy, greyish white drink produced traditionally from mare's milk in easternEurope and central Asia.

It can have an acidity up to 1.4% and an ethanol content up to 2.5%.

A mixed yeast/LAB flora is responsible for the fermentation comprising Lb. delbrueckiisubsp. bulgaricus and a number of lactose fermenting yeasts.

These are dispersed throughout the product and do not form discrete particles as in kefir.

Cow's milk is a more convenient raw material to use nowadays and this is usuallymodified to resemble more closely the composition of mare's milk which has a lower fatcontent and higher carbohydrate levels.

Koumiss

Strictly speaking, buttermilk is the liquid which separates from cream during thechurning of butter. However, to achieve a consistent quality product most buttermilk today is produceddirectly by the fermentation of skimmed or partially skimmed milk. Cultured buttermilkis an acidic refreshing drink with a distinctive buttery flavour.

A mixture of starter organisms are required to produce these attributes;Lactococcus lactis produces most of the lactic acid, while the buttery flavour is the resultof diacetyl production by so-called flavour bacteria such as strains of Lactococcus lactissubsp. lactis and Leuconostoc mesenteroides subsp. cremoris.

Fresh milk contains citrate but levels decline during storage so that, for the productionof cultured buttermilk, the milk is often supplemented with 0.1-0.2% sodium citrate toensure good flavour development.

Pasteurized, homogenized milk is fermented at 22 0C for 12-16 h. The product contains0.7-0.9% lactic acid and will keep for two weeks at 5 0C

Another property of LAB valued in some fermented milks is their ability to produce aglycoprotein slime which provides a characteristic texture and viscosity to products suchas Swedish langjil and Finnish villi.

Buttermilk

Mold-lactic fermentation results in a unique Finnish fermented milk called viili. The milkis placed in a cup and inoculated with a mixture of the fungus Geotrichium candidum andlactic acid bacteria.

The cream rises to the surface, and after incubation at 18 to 20°C for 24 hours, lactic acidreaches a concentration of 0.9%.

The fungus forms a velvety layer across the top of the final product, which also can bemade with a bottom fruit layer.

Mold-Lactic Fermentation of Milk

Viili

Cheese

Cheese Production

Developed approximately 8,000 years ago and more than 2,000 distinct varieties of cheeseare produced throughout the world, representing approximately approximately 20 generaltypes. 78 different types of blue cheese and 36 Camemberts alone

Cheeses are classified based on texture or hardness as soft cheeses (cottage, cream, Brie), semisoft cheeses(Muenster, Limburger, blue), hard cheeses (cheddar, Colby, Swiss), or very hard cheeses (Parmesan).

All cheese results from a lactic acid fermentation of milk, which results in coagulation of milk proteins and formation of a curd.

Rennin, an enzyme from calf stomachs, but now produced by genetically engineered microorganisms, can also be used to promote curd formation.

Chymosin

After the curdling it is heated and pressed to remove the watery part of the milk (called the whey), salted, and then usually ripened.

The cheese curd can be packaged for ripening with or without additional microorganisms.

Lactococcus lactis is used as a starter culture for a number of cheeses including Gouda (figure 40.14a) and cheddar (figure 40.15).

Starter culture density is often over 109 colony forming units (CFUs) per gram of cheese before ripening. However, the high salt, low pH, and the temperatures that characterize the cheese microenvironment reduce these numbers rather quickly.

This enables other bacteria, sometimes called nonstarter lactic acid bacteria (NSLAB) to grow; their numbers can reach 107 to 109 CFUs/g after several months of aging.

Thus both starter and nonstarter LAB contribute to the final taste, texture, odor, and appearance of the cheese.

‘Dessert without cheese is like a pretty woman with only one eye’

In some cases, molds are used to further enhance the cheese.

Obvious examples are Roquefort and blue cheese. For these cheeses, Penicilliumroqueforti spores are added to the curds just before the final cheese processing.

Sometimes the surface of an already formed cheese is inoculated at the start ofripening; for example, Camembert cheese is inoculated with spores of Penicilliumcamemberti.

The final hardness of the cheese is partially a function of the length of ripening. Softcheeses are ripened for only about 1 to 5 months, whereas hard cheeses need 3 to 12months, and very hard cheeses like Parmesan require 12 to 16 months ripening.

The ripening process also is critical for Swiss cheese. Gas production byPropionibacterium contributes to final flavor development and hole or eye formation inthis cheese.

Some cheeses are soaked in brine to stimulate the development of specific fungi andbacteria; Limburger is one such cheese.

Cow's milk for cheese production must be free from antibiotics and sanitizing agentsthat might interfere with the fermentation.

Cheeses made from raw (unpasteurized) milk have been claimed to possess a betterflavour

The starter organisms used in most cheesemaking are described as mesophilic starters,strains of Lactococcus lactis and its subspecies.

Thermophilic starters such as Lactobacillus helveticus, Lb. casei, Lb. lactis, Lb.delbrueckii subsp. bulgaricus and Strep. thermophilus are used in the production ofcheeses like Emmental and Parmesan where a higher incubation temperature isemployed

The thermophilic lactobacilli, which employ a lactose permease and P-galactosidase,metabolize the glucose produced preferentially, turning to galactose only when lactosebecomes limiting,

The accumulation of galactose can give rise to a brown discolouration problem during theheat processing of Mozzarella cheese.

In Swiss cheeses such as Emmental, residual galactose can affect product flavour sincepropionic acid bacteria ferment it in preference to lactate.

In doing so they produce a preponderance of acetic (ethanoic)acid which does not conferthe usual nutty flavour associated with the equimolar concentrations of acetate andpropionate produced by the Propionibac terium from lactate .

Citrate fermentation to diacetyl is required in some cheese varieties and starter culturesfor these include species such as Lactococcus Zactis subsp. Zactis or Leuconostoc cremoris.

Carbon dioxide is another product of this pathway and is important in producing thesmall eyes in Dutch cheese like Gouda or giving an open texture that will facilitate mouldgrowth in blue-veined cheeses.

In other cheese, such as Cheddar, this would be regarded as a textural defect.

The cheese is ripened or matured at 10 0C to allow flavour development.

During this stage, which can last up to five months to produce a mild Cheddar, themicroflora is dominated by non-starter lactobacilli and a complex combination of bacterialand enzymic reactions give the cheese its characteristic flavour.

In particular, proteases and peptidases from the starter culture continue to act, eventhough the organism can no longer grow.

With other proteases from the rennet, they release free amino acids (principallyglutamic acid and leucine in Cheddar) and peptides which contribute to the cheese flavour.

In some cases this can give rise to a flavour defect: casein proteins contain a highproportion of hydrophobic amino acid residues such as leucine, proline and phenylalanineand if they are degraded to produce peptides rich in hydrophobic residues, the cheese willhave a bitter taste.

The lipolytic and proteolytic activities of moulds play an important role in the maturation of some cheeses.

In blue cheeses such as Stilton, Penicillium ruquefurtii grows throughout the cheese. It can grow at reduced oxygen tensions, but aeration is improved by not pressing the curds and by piercing the blocks of curd with needles.

P. camembertii is associated with surface-ripened soft cheeses such as Camembert and Brie.

Plant based fermentation products:

{Pickles, Sauerkraut, Kimchi, Olives & Cucumbers}

Soybeans are one of the most important protein sources for millions of people in theOrient; one of the most popular products for centuries has been soy sauce.

Soy sauce is a liquid food condiment prepared from fermented rice or wheat andsoybean with the help of molds, bacteria, and yeasts.

Soy sauce is known as ch’au yau or pak yau in China, shoyu in Japan, ketjap inMalaysia, kecap in Indonesia, kenjang in Korea, toyo in the Philippines, and see-ieuin Thailand.

It is said that soy sauce became popular in Japan as a result of the introduction ofBuddhism from China. The Chinese have been using soy sauce for over 3000 yr.

Soy Sauce

Miso is a fermented soybean paste that is believed to have originated in China in 600A.D. or earlier.

It is known as chiang in China, miso in Japan, jang or deoenjang in Korea, tauco inIndonesia, taochieo in Thailand, and tao-si in the Philippines.

Most of these products contain rice or barley fermented by Aspergillus oryzae, whichmakes koji. This is mixed with soybeans and fermented for several months.

Miso has been popular in Japan for over 1000 yr and is used as a base for soups, asauce served with meat, or poultry, seafood, and vegetable dishes.

Miso

Tempeh

One of the most important products of Indonesia is tempeh, which is made from soybeanfermented with the mold Rhizopus.

It is particularly important in Java and Bali. It is also produced in Malaysian villages,Singapore, Canada, Holland, the West Indies and the United States.

Sake

Other Fermented Foods (Sufu)

Many other plant products can be fermented using microbes (cabbage, cucumbers andolives)

These include sufu, which is produced by the fermentation of tofu, a chemicallycoagulated soybean milk product.

To carry out the fermentation, the tofu curd is cut into small chunks and dipped into asolution of salt and citric acid.

After the cubes are heated to pasteurize their surfaces, the fungi Actinimucor elegans andsome Mucor species are added.

When a white mycelium develops, the cubes, now called pehtze, are aged in salted ricewine.

This product has achieved the status of a delicacy in many parts of the Western world.

Another popular product is tempeh, a soybean mash fermented by Rhizopus.

A biogenic amine is a biogenic substance with one or more amine groups. Theyare basic nitrogenous compounds formed mainly by decarboxylation of aminoacids or by amination and transamination of aldehydes and ketones.

Biogenic amine

Sauerkraut or sour cabbage is produced from wilted, shredded cabbage.

Usually the mixed microbial community of the cabbage is used.

A concentration of 2.2 to 2.8% sodium chloride restricts the growth of gram-negativebacteria while favoring the development of the lactic acid bacteria.

The primary microorganisms contributing to this product are Leuconostoc mesenteroidesand Lactobacillus plantarum.

A predictable microbial succession occurs in sauerkraut’s development.

The activities of the lactic acid-producing cocci usually cease when the acid contentreaches 0.7 to 1.0%.

At this point Lactobacillus plantarum and Lactobacillus brevis continue to function. Thefinal acidity is generally 1.6 to 1.8, with lactic acid comprising 1.0 to 1.3% of the total acidin a satisfactory product.

Sauerkraut

The salt serves a number of purposes:

(i) Extracts moisture from the shredded cabbage by osmosis to form the brine inwhich the fermentation will take place;

(ii) Inhibit some of the natural microflora of the cabbage such aspseudomonads which would otherwise cause spoilage and helps to select forthe lactic acid bacteria;

(iii) Helps maintain the crisp texture of the cabbage by withdrawing water andinhibiting endogenous pectolytic enzymes which cause the product to soften;

(iv) Salt also contributes to the flavour of the product.

Defects of sauerkraut arise mostly as a result of yeast and mould growth

Pickles are produced by placing cucumbers and such components as dill seeds in casks filled with a brine.

The sodium chloride concentration begins at 5% and rises to about 16% in 6 to 9 weeks.

The salt not only inhibits the growth of undesirable bacteria but also extracts water and water-soluble constituentsfrom the cucumbers.

These soluble carbohydrates are converted to lactic acid.

The fermentation, which can require 10 to 12 days, involves the development of the gram-positive bacteria L.mesenteroides, Enterococcus faecalis, Pediococcus cerevisiae, L. brevis, and L. plantarum. L. plantarum plays thedominant role in this fermentation process.

Sometimes, to achieve more uniform pickle quality, natural microorganisms are first destroyed and the cucumbersare fermented using pure cultures of P. cerevisiae and L. plantarum.

Pickles

Pickled vegetables, made in households or small factories, have been popular in Egypt for centuries.

The vegetables pickled in Egypt include carrots, cucumbers, turnips, cauliflower, green and black olives, onions,and peppers.

Pickled vegetables are used as appetizers and served with practically every meal. Homemade pickles made fromfruits and vegetables are called jeruk in Malaysia.

Cucumber is one of the oldest vegetables cultivated continuously by people. It is thought to have had its origin inIndia more than 3000 yr ago. It is utilized both as a fresh vegetable and a pickled product.

Grass, chopped corn, and other fresh animal feeds, if stored under moist anoxicconditions, will undergo a lactic-type mixed fermentation that produces pleasant-smellingsilage.

Trenches or more traditional vertical steel or concrete silos are used to store the silage.The accumulation of organic acids in silage can cause rapid deterioration of these silos.

Older wooden stave silos, if not properly maintained, allow the outer portions of thesilage to become oxic, resulting in spoilage of a large portion of the plant material.

Kimchi In Korea fermented vegetables known as kimchi are an almost ubiquitous accompaniment tomeals.

More than 65 different types of kimchi have been identified on the basis of differences in rawmaterials and processing.

Cabbages and radishes are the main substrates but garlic, peppers, onions and ginger are oftenalso used.

Surveys have shown its importance in the Korean diet, variously reporting kimchi to comprise12.5% of the total daily food intake or a daily adult consumption of 50-100 g in summer increasingto 150-200 g in winter.

Kimchi is similar to sauerkraut in some respects since cabbage is a common ingredient and thelevel of salt used is low (<3%).

It differs principally in having a shorter fermentation time; the best taste is claimed after 3 daysat 20 oC when the acidity is 0.6% and the pH around 4.2.

Consequently Leuconostoc mesenteroides is the principal organism responsible for thefermentation and dominance of Lactobacihs plantarum is regarded as a defect which results in anexcessively sour product.

Kimchi

Kimchi is the general name given to a group of acid fermented vegetable foods that havea long tradition in Korea.

More specific names are used for these pickled vegetables, depending on the rawmaterial, processing methods, season of the year, and locality.

42 Kimchi is a popular side dish served at every meal along with cooked rice and otherdishes and is made primarily from cabbage or radish.

Olives

Olives are one of the oldest fruit crops in the Mediterranean area.

The exact date when olive fermentation started is not known. However, the more recent historyof the table olive industry in California has been well documented.

Between 1870 and 1900, many varieties of olives were imported from the Mediterranean area.Olives were used for oil production in the Californian missions as early as 1780.

The olive literature of California contains directions for pickling of ripe and green olives thatwere used in the home for many years; olive pickling became commercialized by 1900.

Five processes for pickling olives in Mediterranean countries: Spanish green olive, Frenchbrine, dry salt, water, and Italian dried. In the first two processes, lye (a strongly alkaline solution,especially of potassium hydroxide) is used to destroy the bitter glucoside found in olives.

Four types of fermented olives—California-ripe, brined Greek-type, Siciliano-type green, andSpanish-type green—are reported by Vaughn.

The extent of lye treatment, salting, and the period of fermentation varies with different types ofolives, but the main organisms causing fermentation in all these varieties are Lactobacillusplantarum, Lb. casei, and Leuconostoc mesenteroides.

In the production of Spanish-style green olives, which account for 38% of worldproduction, the unripe fruits are first treated with lye (1 .O-2.6% sodium hydroxidesolution/10h) to hydrolyse the glucoside oleuropein which imparts a bitter flavour andalso inhibits lactic acid bacteria

Most important species appears to be Lactobacillus Plantarum with Several other LAB have been reported, including an early phase of growth by Leuconostoc mesenteroides

To control the fermentation air is excluded from the fermenting product to prevent the growth of oxidative moulds and yeasts

Dill is an annual, self-seeding plant with featherygreen leaves. It is used most commonly in soups,stews, and for pickling.

Cucumbers

Despite this recent trend, fermentation does have a number of advantages overother methods.

(1) Fermented cucumbers have flavour and texture characteristics not possessed by theother products.

(2) Bulk fermentation techniques facilitate quick and easy processing in busy harvestseasons.

(3) Under these conditions, products can be stored in bulk until they are required forfurther processing, so that year-round working is possible.

(4) Fermentation is more economical with energy than techniques which requirepasteurization or an efficient cold chain.

Cucumber fermentations can be divided into essentially two different types: high-salt, or salt stock, and low-salt fermentations Direct acidification with vinegar or acetic acid followed by pasteurization (Current trend)

Genuine dill pickles are fermented in a lower salt brine (3-5%) in the presence of dill and spices.

Production of Alcoholic Beverages

A variety of plants carbohydrates can be used to produce alcoholic beverages.

Grapes are crushed to release the juice or must, which can be allowed to ferment

The must also can be treated by pasteurization or the use of sulfur dioxide, and then thedesired microbial culture added

The complex carbohydrates of cereals must be hydrolyzed before the production ofalcohol

They are mixed with water and incubated in a process called mashing.

The insoluble material is then removed to yield the wort, a clear liquid containingfermentable sugars and other simple molecules

Beer and ale production involves the controlled hydrolysis of protein and carbohydratesto provide the desired flavor

Yeast Fermentations

Table 28.5

Beers and Ales

Beer and ale production uses cereal grains such as barley, wheat, and rice.

The complex starches and proteins in these grains must be changed to a more readilyusable mixture of simpler carbohydrates and amino acids.

Germination of the barley grains and activation of their enzymes to produce a malt.

The malt is then mixed with water and the desired grains, and the mixture is transferredto the mash tun or cask in order to hydrolyze the starch to usable carbohydrates.

The mash is heated with hops (dried flowers of the female vine Humulus lupulis), whichwere originally added to the mash to inhibit spoilage microorganisms

The hops also provide flavor and assist in clarification of the wort.

In this heating step the hydrolytic enzymes are inactivated and the wort can be pitched—inoculated—with the desired yeast.

Most beers are fermented with bottom yeasts, related to Saccharomyces pastorianus, whichsettle at the bottom of the fermentation vat.

The beer flavor also is influenced by the production of small amounts of glycerol and aceticacid.

Bottom yeasts require 7 to 12 days of fermentation to produce beer with a pH of 4.1 to 4.2.

With a top yeast, such as Saccharomyces cerevisiae, the pH is lowered to 3.8 to produceales.

Freshly fermented (green) beers are aged or lagered, and when they are bottled, CO2 isusually added.

Beer can be pasteurized at 140 °F or higher or sterilized by passage through membranefilters to minimize flavor changes.

Making Red Wine

Figure 28.9

Wine production, or the science of enology starts with the collection of grapes,continues with their crushing and the separation of the liquid (must) before fermentation,and concludes with a variety of storage and aging steps.

All grapes have white juices.

To make a red wine from a red grape, the grape skins are allowed to remain in contactwith the must before Fermentation to release their skin coloring components.

Wines can be produced by using the natural grape skin microorganisms, but this naturalmixture of bacteria and yeasts gives unpredictable fermentation results.

To avoid such problems, fresh must is treated with a sulfur dioxide fumigant and adesired strain of the yeast Saccharomyces cerevisiae or S. ellipsoideus is added.

After inoculation the juice is fermented for 3 to 5 days at temperatures between 20 and28°C. Depending on the alcohol tolerance of the yeast strain (the alcohol eventually killsthe yeast that produced it), the final product may contain 10 to 14% alcohol.

Wines and Champagnes

Clearing and development of flavor occur during the aging process.

The malolactic fermentation is an important part of wine production. Grapejuice contains high levels of organic acids, including malic and tartaric acids.

If the levels of these acids are not decreased during the fermentation process,the wine will be too acidic, and have poor stability and “mouth feel.” Thisessential fermentation is carried out by the bacteria Leuconostoc oenos, L.plantarum, L. hilgardii, L. brevis, and L. casei.

The activities of these microbes transform malic acid (a four-carbontricarboxylic acid) to lactic acid (a three-carbon monocarboxylic acid) and carbondioxide.

This results in deacidification (pH increase), improvement of flavor stability,and in some cases the possible accumulation of bacteriocins in the wines.

A critical part of wine making involves the choice of whether to produce a dry (noremaining free sugar) or a sweeter (varying amounts of free sugar) wine. This can becontrolled by regulating the initial must sugar concentration. With higher levels of sugar,alcohol will accumulate and inhibit the fermentation before the sugar can be completelyused, thus producing a sweeter wine

During final fermentation in the aging process, flavoring compounds accumulate andinfluence the bouquet of the wine.

Microbial growth during the fermentation process produces sediments, which areremoved during racking.

Racking can be carried out at the time the fermented wine is transferred to bottles orcasks for aging or even after the wine is placed in bottles.

Many processing variations can be used during wine production. The wine can bedistilled to make a “burned wine” or brandy.

Acetobacter and Gluconobacter can be allowed to oxidize the ethanol to acetic acidand form a wine vinegar. In the past an acetic acid generator was used to recirculate thewine over a bed of wood chips, where the desired microorganisms developed as asurface growth.

Today the process is carried out in large aerobic submerged cultures under muchmore controlled conditions.

Natural champagnes are produced by continuing the fermentation in bottles toproduce a naturally sparkling wine.

Sediments that remain are collected in the necks of inverted champagne bottles afterthe bottles have been carefully turned. The necks of the bottles are then frozen and thecorks removed to disgorge the accumulated sediments.

The bottles are refilled with clear champagne from another disgorged bottle, and theproduct is ready for final packaging and labelling.

Distilled spirits are produced by an extension of beer production processes.

The fermented liquid is boiled, and the volatile components are condensed to yield aproduct with a higher alcohol content than beer.

Rye and bourbon are examples of whiskeys. Rye whiskey must contain at least 51%rye grain, and bourbon must contain at least 51% corn.

Scotch whiskey is made primarily of barley. Usually a sour mash is used; the mash isinoculated with a homolactic (lactic acid is the major fermentation product) bacteriumsuch as Lactobacillus delbrueckii subspecies bulgaricus, which can lower the mash pH toaround 3.8 in 6 to 10 hours.

This limits the development of undesirable organisms.

Vodka and grain alcohols are also produced by distillation.

Gin is vodka to which resinous flavoring agents often juniper berries have been addedto provide a unique aroma and flavor.

Distilled Spirits

What is The Difference Between Beer and Cider?

Beer is not only one of the most popular beverages, but also one of the oldest in thebook. Cider, the newer of the two, was in fact a staple in Britain and is nowgrowing in popularity around the globe, largely as a gluten-free alternative for beerlovers. Beer and cider both are widely consumed all over the world, and yet eventhe most ardent of cider and beer lovers can often not differentiate between the two.

1. Ingredients: “While beer and cider both rely on fermented sugars to produce alcohol, the two start from verydifferent ingredients”. Beer is made from malted barley, whereas cider is made from apple juice. Note: While a beercan contain fruit and other ingredients, no true cider contains malted grains.

2. Process: Beer is produced from brewing and fermenting malted barley, whereas cider (that contains alcohol) isproduced made by fermenting apple juice.

3. Colour: While beer comes in pale, dark and very dark colours, and depends on the malt, cider comes in light yellow,orange or brown colours.

For beer: Pale amber colour from pale malts is the most common one, and dark beer comes from a lager malt base or palemalt mixed with dark malt. The very dark beers come from patent malts.

For cider: They can vary not only in colour but also from completely clear to cloudy with sediment ranges, due to thefiltering between pressing and fermentation.

4. Flavour: When it comes to flavour and variety, cider comes in two types - dry and sweet. Beer is classified in twocategories as well, based on the temperature of the brewing. It is called as ‘lager’ if the brewing takes place in a lowtemperature, and referred to as ‘ale’when brewed at a high temperature.

5. Alcohol Content: Beer and cider tend to have similar alcohol content. However, cider can be alcoholic as well as non-alcoholic, and beer always contains alcohol.

6. Health Benefits: Cider is a powerhouse of antioxidants, particularly polyphenols (linked to protecting against certaintypes of cancers). Due to the beer-making process, naturally occurring polyphenols are often removed by the brewer asthey can cause beer to appear cloudy. Hence, beer falls behind cider in polyphenol concentration. But according to a 2015study conducted by the Harvard School of Public Health, beer may actually be good for your heart (in moderation, ofcourse).