9. chemistry and stages of yeast alcoholic fermentation

Ethanol production

C₆H₁₂O₆2CO₂+2C₂H₅OH

2ATP, 61kJ/glucose, 26%efficiency

During the primary fermentation, the fermentable sugars, mainly maltose and glucose are converted to ethanol and carbon dioxide by the brewing yeast.

The main factors affecting fermentation performance and beer quality

1. The choice of yeast strain

2. The condition of the yeast at the time of pitching

3. The amount of yeast added to the wort

4. The distribution of the yeast in the fermenting wort throughout the fermentation, and the size and geometry of the fermentation vessel

5. Aeration

6. Wort composition and pH

7. Fermentation temperature and pressure

Warm fermentation

Yeast such Saccharomyces cerevisiae are generally fermented at warm temperatures between 15-20°C occasionally as high as 24°C. they generally foam on the surface of the fermenting beer, as during the fermentation process its hydrophobic surface causes the flocs to adhere to CO₂ and rise; because of this they are often referred to as “top fermentating”

Cold fermentation

Lager is beer that is cool fermented at around 6-12C, sediment at the end of fermentation at the bottom of fermentor and is stored for 30 days or longer close to the freezing point. Saccharomyces pastorianus is used in the brewing of lager

10. how fermented products- wine can be classified

According to row materials and technology:

• The grape wine

• The fermented alcoholic beverages

• Fruit wines- made by alcoholic fermentation of fruits or its juices and often with addition of water, saccharose or spirit

• Flavored wines-made from grape of fruit wine with addition of spirits and natural flavored herbs and spices

• Honey wine (mead)- made by alcohol fermentation from natural honey diluted with water and fruit juice also often with addition of herbs and spices

• Wine derivatives- alcoholic beverages with 50% minimum share of wine or honey wine

• Wine like beverages- with minimum 20-45% share of natural fruit juices

• Low alcoholic beverages-made in part by alcoholic fermentation of grape or fruit juiced or by partial removal of alcohol from grape wines.

According to taste and aroma

• Sparkling wine

• Artificially carbonated wine

• Aromatized wine wine of mass

According to color

• White

• Pink

• Red

According to sugar content

• Dessert wines (white, red)

• Table wines (white or red)

According to alcohol content

• Light

• Medium

• Strong

11. Compare chemical composition of fruit juices and barley wort

• Sugars - glucose, fructose, sucrose

• Organic acids - citric, malic, tartaric, lactic, acetic

• Nitrogen substances - proteins

• Pectins - poligalacturonic acid and ramnose

• Tannins - gallus acid, tannins, catechins, anthocyanins

• Aroma substances - esters, alcohols, aldehydes, ketones, hydrocarbons

• Minerals - ash 0,5% (K, Ca, Mg, Na, P, S, Cl)

• Witamines - C, A (caroten), B group (B1, B2, PP).

12. Main processes during winemarking

Stages:

• harvesting and transportation

• washing and selection

• crushing and pressing

• fermentation

juice

pomace

• first racking

• aging, maturation and fining

• filtration and pasteurization

• bottling

13. Why SO₂ is used in winemarking

Sulphur dioxide is the most widely used additive in wine making with role to inhibit or kill unwanted yeasts and bacteria and to protect wine from oxidation.

oxidation is the reaction of wine with oxygen. it can alter its colour and odour and is often dismisses as a fault.

SO₂ is added at several points in the vinification and is present in the finished wine as sulphites. there 3 points where sulphur dioxide is commonly used: crushing, fermentation, bottling.

14. What we expect from wine's yeasts

- alcohol toleration

-can establish a viable population in an environment of high sugar (190-270 grams per litre) and high acidity

-are resistance to CO₂ concentration

-are strong and consistent fermenters even at cold temperatures

-they ferment quickly and only stop when all sugars have been utillised

-are more tolerant to sulfur dioxide than other yeasts and bacteria

-they produce wine like aroma and flavor characters

-special yeast for sparkling, sulfited, red (tannins), different fruits

15. Factors effecting the course of fermentation

-carbon sources (monosaccharides)

-nitrogen sources (amino acids, ammonium salts)

-minerals (Mg, K, Zn, Co, J, Fe, Ca, Cu, P, S)

-alcohol (inhibition at high concentration)

-carbon dioxide (high level can stopped yeast growth)

-acids (low pH reduce fermentation)

-growth factors (biotin, inositol, nicotinic, acid, thamine)

-tannins (in some cases inhibit yeast growth)

-temperature (optimum 22-27C)

-oxygen (essential for yeast growth, absent during fermentation, controlled during maturation)

16. What has to be done with wine after fermentation

*After fermentation wine has to be storaged, while this it is aging.

-oak containers are preferred

-tanks must be filled up and sealed to prevent acetification

-the bouquet develops (row materials, fermentation, maturation)

-yeast odor and harsh taste disappear

-temperature is lowered to 5-12 C for dry and semi dry wines, to 18C for sweet wines and also for red wines

-correction of acidity occurs

-process last from few to years with several yeast racking (red table wines 1-4 years, white table years 1-2 years, polish fruit wines popular 3 months and mark 6 months)

*accelerated maturation:
-cooling
-refrigeration
-slow oxidation
-heating (pasteurization)
-exposure to sunlight, UV light

*wine stabilization and filtration
Clarification of wines by fining with addition of substances which react with tannins, acids, proteins (gelatin, casein etc.).

17. Give a short description of main types of fortified wines.

We can discern a main 3 basic groups of fortified wines: Port, Sherry and Madeira (final alcohol level 15-22%)

Port - is made mainly with red grapes. Is a kind of sweet wine. Fortified to 20% by the addition of a neutral grape spirit (brandy).

Sherry - mainly white, dry wine. Brandy is adding to the wine after fermentation.

Madeira - can be made like Sherry (the sugar is almost fully fermented before the brandy is added) or closer to the way like Port is made (interrupting the fermentation with grape spirit leaving residual sugar in the Madeira).

1. Enumerate and briefly characterized functional additives used in bakery technology

• Enzymes

• Emulsifiers

• Oxidizing and reducing agents

• Hydrocolloids

• Acidifiers

Applied to:

• improve sensory characteristic of the product, taste, smell, appearance, volume, texture

• extend shelf life

• improve machine ability of the dough

• raise profitability: shorter production process, lower workload, reduce number of fermentation vessels, replacement of expensive ingredients

Enzymes- amylases (α and β)- fungal, bacterial enzymes or malt- good dough and bread texture (fermentable sugar),

Proteases- bacterial and plant enzymes- better dough elasticity and extensibility, shorten mixing and proofing time

Oxidoreductases- lipoxidases- strengthened dough structure, flour bleaching

Emulsifiers- surface active agents able to form starch-protein-fat-water complex

• ionic- improved dough handling and gas retention

• non-ionic- longer bread shelf life

• lecithin- plant oils or eggs isolate- increase dough nie mam zapisane co dalej prosze aby ktoś uzupełnił

Oxidants- potassium brodate, ascorbic acid- increase of flour hydration, improved dough reological properties and gas retention, flour bleaching

Hydrocolloids- substance that form a gel with water

• plant secretions or extracts, powdered seeds,

• microbiological gums

• synthetic gum

Increase of dough yield, prolonged shelf life, improved crumb quality

Organic acid and their salts:

• lactic, citric, tartaric or acetic acid and their salts

• dried sourdough with acids addition

• quick dough acidification

2. Explain the role of bakery starter cultures

• Initiation of the fermentation process

• Obtaining the desired baking parameters of dough

• Due to the biochemical changes in the fermented flour

• Stability of the fermentation process

• Shortening and simplifying sourdough production

• Obtaining the unique and very attractive taste and flavor of the bread

• Bread of high nutritional value

• Reduction or elimination of artificial improvers and preservatives

• Repeatability of bread quality

• Prolonged shelf life or sourdough bread

3. Indicate and briefly characterized the new technologies in bread production

• Dried sourdough- dried full sour (direct dough preparation, used as a starter culture)

• Liquid sourdough- rich in aroma, easy to handle

• Delayed dough fermentation (retarded dough)- delay in dough fermentation caused by low temp. application

• Delayed bread baking- separation (in time and/or in place) between the dough preparation and the baking by freezing of semi-products

• Dried sour dough- sourdough prepared with a high yield >200, preserved by water removal

• Freeze drying (lyophilisation)- dehydration process, base on water evaporation from the solid phase (ice), weaker aroma, removal of volatiles

• Fluid bed drying - heat supplied by hot air, formation of aroma compounds typical for baked potatoes

• Prolonged fermentation in ambient temp- lower yeast dosage (1,5-2%), ambient temp, leaving time 3-6h.

• Blocked dough leavening- nie zapisałam bo pewnie nie dałam rady

• Blocked incomplete dough leavening- fermentation in temp 25C, obtaining 1/3 -3/4 of full volume, blockade at temp.

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