Food and beverage fermentations

Food and beverage fermentationsMicroorganisms have long played a major role in the production of food and beverages. Fermented foodstuffs include: alcoholic beverages (beers, wines) dairy products (cheeses, yoghurt) fish and meat products (fish sauce) plant products (cereal-based breads and fermented rice products)

Food and beverage fermentations Many of these products originally evolved as a means of food preservation. Importantly, besides providing long-term stability, these fermentation processes also generate desirable flavour, aroma and texture.The role of microorganisms in this field is used as novel food, such as single cell protein speciality mushrooms and probiotic preparations.

Food and beverage fermentationsfermentation products are also incorporated as food additives and supplements,

In addition, microbial enzymes are utilized extensively as food processing aids, and some may be added to animal feed to improve its nutritional value.

Alcoholic beveragesAlcoholic beverages have been produced throughout recorded human history. They are manufactured worldwide from locally available fermentable materials, which are sugars derived either from fruit juices, plant sap and honey, or from hydrolysed grain and root starch.

Alcoholic beverages cont.Although bacteria such as Zymomonasspecies may be involved in the production of certain products, yeasts are primarily used, either in single or mixed cultures. The yeasts involved in these alcoholic fermentations are mostly strains of Saccharomyces cerevisiae, which cannot directly ferment starch.

Beer brewingThe term beer is given to non-distilled alcoholic beverages made from partially germinated cereal grains, referred to as malt. They include ales, lagers and stouts, which normally contain 38% (v/v) ethanol.Their other main ingredients are hops, water, and yeast.

Beer brewingThe brewing process is essentially divided into four main stages: Malt and Malting Mashing and Wort preparation Yeast fermentation Post-fermentation treatments

Malt and Malting

Malting involves the controlled partial germination of barley grain. This modifies the hard vitreous grain into a friable (easily crushed) form containing more readily degradable starch and generates hydrolytic enzymes, especially amylases, b-glucanases and proteases.

Malt and Malting cont.Barley grains contain approximately 65% starch, located within the endosperm region and their walls are composed of a mixed linkage b-glucan (b-1,3; 1,4), hemicellulosic pentosans and protein. Malting begins by soaking or steeping the barley in water for 2 days at 1016C, in order to increase the moisture content to around 45% (w/w). After steeping, the barley is partially germinated for 35 days at 1619C.

Malt and Malting cont.Grain modification can be promoted in several ways.Abrasion improves access of water and any additives. The application of the plant hormone gibberellic acid, at levels of 0.10.5 mg/kg barley, may be made to augment the natural embryo-produced hormone that stimulates de novo synthesis of certain hydrolytic enzymes, including a-amylase.

Malt and Malting cont.Cellulase supplements, such as enzymes from Trichoderma reesei, at levels of 2448mg/kg barley, also speed germination by aiding endosperm cell wall breakage.

Malt and Malting cont.The malt is kilned via a two-stage process. First it is dried at 5060C and then cured at 80110C. Kilning takes about 2 days and has several functions.It arrests embryo growth and enzyme activity,develops flavour and colourPale lager malts that require little color development are subjected to mild conditions.

Malt and Malting cont.Highly colored malts required for flavouring and coloring dark beers have low enzyme activity. At a final moisture content of 23% (w/w), the malt is biologically stable for several months.

Wort preparationThe objectives of wort preparation are to form, and extract into solution, fermentable sugars, amino acids, vitamins, etc., from malt and other solid ingredients.In some cases, a portion of the adjunct may be in the form of sugar syrups that may be added later during wort boiling.Replacement of some malt with adjuncts is mainly for economic reasons.

Wort preparation cont.Certain adjuncts, such as rice products, may improve specific beer properties, but contribute little flavor and enzyme activity.Other mash adjuncts include raw barley, wheat flour, maize grits, and other flaked or micronized cereals.Traditionally, 510% (w/w) malt was added during cooking to provide amylases that hasten the process.

Wort preparation cont.Malt and those adjuncts requiring milling are usually roller-milled prior to mashing. This is often performed in such a way as to largely retain the husk intact, The husk later acts as a filtration aid in wort separation. Milled ingredients are transported to the mash vessel and mixed with hot water, the brewing liquor, whose composition can influence final beer quality.

Wort preparation cont.Following mashing the liquid extract is separated from residual solids to form the wort, which must then be stabilized by boiling. Resulting wort should be a well-balanced liquid medium that will supply the yeasts with all nutritional requirements for the subsequent fermentation.

Mashing SystemThree main mashing systems are operated:

1. Infusion mashing- is the classic British method for ales and stouts, using well-modified malt and relatively simple equipment. Solid mash ingredients are mixed with hot brewing liquor to achieve a mash temperature of 6265C.

Infusion mashing cont.

The mash has a liquor to solids (grist) ratio of around 3: 1 and this thick mash helps to stabilize some malt enzymes.Mashing lasts for 12 h and is followed by mash sparging. This involves spraying water at 7075C, which percolates and washes out the soluble extract.

Infusion mashing cont.

The grain bed sits on the false bottom of the mash tun, which has slots approximately 1 mm wide.Resultant liquid extract Sparging is continued until the specific gravity of the wort falls to a specified level indicating that little or no more soluble sugars remain in the mash,it is called sweet wort.

Mashing System

2. Decoction mashing - has been traditionally used in Europe and is suitable for less well-modified malts. The initial mash temperature starts at around 3540C, with a liquor to grist ratio of up to 5 : 1.I nitial lower temperature facilitates hydrolysis of b-glucan and protein, and is often called a protein rest.

Decoction mashing cont.

The temperature is then raised to 5055C,The aim is to raise the temperature stepwise to about 65C, to achieve starch degradation, and finally to 75C.

Mashing System3. Temperature programmed mashing systems - are operated by many modern breweries. The mash temperature is raised using a heating jacket from around 40C to above 70C.The result of mashing, irrespective of the system used, is an aqueous extract, the sweet wort, and insoluble spent grains

Biochemistry of mashing

Starch hydrolysis - The objective in mashing is to convert as much of the malt and adjunct starch as possible to fermentable sugars. Starch is composed of 25% amylose, a linear polymer of a-1,4-linked glucose units, and 75% amylopectin, which is a branched polymer containing both a-1,4 and a-1,6 linkages.

Starch hydrolysis cont.b-Amylase is an exo-enzyme that hydrolyses alternate a-1,4 linkages from the non-reducing ends of polymers to release disaccharide maltose units. This enzyme operates mainly after the initial dextrinization of starch and ultimately generates glucose, maltose and maltotriose units.

Starch hydrolysis cont.Malt enzymes that are most likely to be limiting are b-amylase and limit dextrinase, which are more thermolabile than a-amylase. Well-modified malt normally contains 34 times more a-amylase than is required for mashing. Non-fermentable residual dextrins normally constitute approximately 2025% of the original starch.

Starch hydrolysis cont.The production of low-carbohydrate beers, is often facilitated through the addition of commercial debranching enzymes, e.g. isoamylases, pullulanases or amyloglucosidases. Amyloglucosidases from Aspergillus niger, Rhizopus species or Schwanniomyces castellii are most frequently used for this purpose.

Biochemistry of mashingb-Glucan hydrolysis - Cell wall b-glucan is solubilized during malting and mashing by b-glucan solubilase and then degraded by malt endo-b-glucanases. Its hydrolysis is crucial, as undegraded b-glucan may cause slow wort separation, beer filtration problems and hazes. It also reduces potential extract yield from the mash

Biochemistry of mashing

Wort separation and beer filtration is aided by supplementing the mash with Trichoderma cellulase-complex or a thermostable b-glucanase from Bacillus subtilis. Added pentosanases may be useful in the degradation of cell wall, However, resultant pentose sugars are not fermented by brewing yeast.

Biochemistry of mashing

Protein hydrolysis - Barley malt has an extensive range of Proteases. Their role in mashing is to degrade wall and matrix proteins of endosperm cells. This allows amylases access to starch granules and generates a well-balanced spectrum of amino acids for subsequent yeast fermentation.

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