Etiket Arşivleri: Yeast nutrition
• What is yeast nutrition?
• Why is it important?
• Current understanding of the needs and challenges
• Utilization of nutrients to rectifyidentified challenges
WHAT IS YEAST NUTRITION?
• Yeast cell physiology
– Refers to how yeast cells feed, metabolize, grow, reproduce, survive and ultimately die
• Yeast nutrition
– Mechanisms of how yeast cells translocate water and essential organic and inorganic nutrients from the surrounding environment, through the cell wall, across the cellular membrane and into the intracellular milieu
Grain Beer ( 3-12 % alcohol )
Fruit Wine ( 11-15 % alcohol, 22% fortified”sherry,port” )
the best examples of “value added” processing…the fermentation of grapes into wine.
On a per capita basis, consumers in Luxembourg, France,and Italy drink the most wine, more than 50 liters per person per year).
This compares to the world per capita average of about 3.5 liters.
Türkiye ….0.26 liters (2005)
France Italy and Spain are biggest producers
Historical background :
It is assumed to be consumed before the beginning of recorded history. The research of Louis Pasteur revolutionized the wine industry ( 1840- bacteria is detrimental to wine). Dom Perignon discovered that ( 1679) when wine is fermented after bottling, the bubbles it creates will remain in the wine so, he is considered as founder of champagne.
Sucrose: less than 1% except for musts from V. Labrusca grapes( which can contain as much as 10% sucrose.)
In general, most grape cultivars contain about 20% sugar (i.e., 10% glucose and 10% fructose),
Juice from mature grapes at 20% sugar is ordinarily about 21°Brix to 24°Brix.
Grapes: Vitis vinifera family ( Europian ): From Spain to California
Vitis lobrusca family ( American) : Newyork More acid, low sugar, slippy skin)
many species, many varieties, differs from year to year and differ due to local soil and climate.
For harvesting soluble solids
(S.S.) is checked.
When it reaches to highest value (18-21%)
it should be picked immediately.
Nature of Microbial Process :
Kloeckera apiculata and Candida pulchermia and stellata are naturally exist on the skin of grape and they produce ethanol up to 5 %. After this level Saccharomyces cerevisiae over grown the above microorganisms.
Now pure cultures of Saccharomyces cerevisiae var ellipsoideus and var vini are being used.
By products :
glycerol (2.5-3 %, accumulates during initial stages of fermentation.), One of the most important fermentation byproduct, which is a major contributory factor in forming the body of the wine.
acetic acid ( 0.05-0.65 %, produced during early stages of fermentation),
acetaldehyde ( 0.01-0.04 %, some converted to acetoin and than to 2,3-butanediol ),
2.3-butanediol ( 0.06-0.1 %),
succinic acid (0.02-0.05 % )
higher alcohols ( 0.01-0.04 %).
Level of all of these products are strongly influenced by yeast strain and environmental conditions, especially temperature.
Desired properties of a wine yeast
should produce alcohol up to 18 %
should produce 8-12 % alcohol in a reasonable time at low temperatures ( ie 4-10 C) at reasonably high sulfur concentration ( at low rH, redox potential ,it should be able to grow)
should be able to grow on 30 % sugar solution ( osmophilic yeast )
Effect of temperature on wine fermentation
Alcohol yield, rate of fermentation, concentration and proportions of by products, flavor compound formation = f ( temperature of fermentation)
More flavor (aromatic)compound is formed in wine by long, slow, low temperature fermentation
White wines are typically fermented at cooler temperatures (about 15 °C) than red wines (about 20 °C) to enhance the production and retention of ‘fruit’ esters synthesized by yeasts, giving the wine a fruity fragrance.
Red wines fermented about 20 °C to facilitate yeast growth in the presence of grape phenolics, and to promote pigment and flavor extraction from the skins.
1 mole glucose alcohol and CO2 DG= – 56 kcal ( free energy loss)
2 ATP ( 14 Kcal ) is recovered and remaining is lost as heat. ( 75 % of the energy is lost as heat)
large fermentation tanks cooling is required to keep the temperature constant.
Use of sulfur dioxide
It is used to -disinfect containers
-control contaminating m.o.’s( kills by inhibiting metabolic enzymes containing S-H groups) also
-combines with carbonyl comp.( ie acetaldehyde ) ,
-unsaturated aliphatic compounds
-proteins of the must. Combined form of the sulfur dioxide is much less toxic to m.o.’s and less effective as antioxidant.
protect wine against excessive oxidation during storage and aging (inactivates polyphenoloxidase enzyme so it prevents darkening of wine color)
small tanks : potassium bisulfite can be added as SO2 source.
large tanks: pressurized SO2 is used.
Yeast needs carbon and energy source, nitrogen, vitamins, minerals.-addition of ammonium salts ( ie (NH4)2HPO4) to sluggish growing yeast.
Wine yeast can ferment hexose sugars but not the pentose sugars.
Self digestion of yeast cells (autolysis, break down of cells): release amino acids and nucleotides, impart undesirable flavor to wine.
Also these released compounds are good food for spoilage ( lactic acid ) bacteria, therefore sediment yeast should be removed as soon as fermentation is completed.
If high acid wine is desired we may want to have autolysis intentionally to support malolactic fermentation
Deacidification of wine
Tartaric and L-malic acids are the major acids in grapes, the former being quantitatively the most important.
However, grapes grown in cool regions, sometimes contain high levels of L-malic acid, leading to an excessive titratible acidity in the wine produced.
two methods to reduce L-malic acid:
The conversion of malic acid ( a dicarboxylic acid ) to lactic acid ( a mono carboxylic acid ) and CO2 during the so called bacterial malolactic fermentation.
Lactobacillus, Pediococcus, Leuconostoc can cause malolactic fermentation. ( during the middle to late stages of alcoholic fermentation)
MAIN STEPS OF WINE MAKING
I-Stemming and crushing:
– crushing :revolving rollers ( garolla crusher).
-separating stems: revolving drum perforated with holes
The resulting crushed grapes ( including seeds and skins) are then collectively termed as “ grape must” or just “must”
II- Addition of sulfur dioxide :
Added immediately after crushing to inhibit the growth of undesirable yeast and bacteria ( 50-100 ppm SO2 added ). (57 % of sulfur is used to produce active SO2 from K2S2O5 )
III- Addition of sugar : if grapes contain less than 22 % sugar an appropriate amount of sugar ( refined sucrose ) is added to bring the must to 22 Brix. to calculate the amount of sugar to be added to yield a gape must of 22 Brix.
Ws = Wa ( B-A) / (100 –B) where;
A : Brix of fresh must
B: Brix of desired must
Wa: weight of the must
Ws: weight of the sugar to be added
IV- Color extraction:
To produce white wine: green grape or red grape with “cold press” to prevent color extraction from skins.
To produce red wine: red grape with “hot press” or “fermentation on the skin” processes.
Pumping over Louis Martini When grapes contain mold( polyphenoloxidase) cause oxidation of the red anthocyanin pigments to compounds with a brown color.
To prevent this heat red grapes to inactivate the enzymes before fermentation .
Heating also helps to release the color from the skins
Hot press :
The must is heated to 62-63 C, pressed while hot, and then cooled immediately to room temperature.
Cause loss of flavor.
Rose’ wine: limited color extraction or mixing red and white wine must
V- Amelioration :add water in the form 22 brix sugar (sucrose ) solution not legal everywhere or limited.
Adjustment of the must to the right quality before the fermentation.(the dilution of the wine by adding water and sugar)
wine grapes may not always reach maturity before harvest: too acidic.
To make quality table wines. ( normal acidity , 0.7-0.9 g/100 ml, PH=3.6 )
VI- Fermentation : ( secondary for red, first for white wine)
Must is pumped into large fermenting vats ( called cooperage ).
CO2 exit is allowed but not the air in to the vessel.
It is inoculated with wine yeast.
Complete fermentation: “dry” wine (takes a few days to a few weeks.)
When some sweetness is desired, the fermentation is stopped while the desired amount of residual grape sugar remains unfermented.
The temperature< 30 C : if not.. loose fragrance and tend to stop the fermentation.
Optimum temperatures for red wine:15-20 C.
White wine: 13-18 C.
During fermentation , SS content of must will decrease first and then stabilizes. ( all the fermentable sugars are depleted.)
Stuck Fermentations ( fermentation fails.)
-significant amount of residual, unfermented sugar
The fermentation: slow or complete standstill.
These slow or halted fermentations are referred to as sluggish or stuck fermentations,respectively.
Stuck wine is especially susceptible to spoilage ( due to low ethanol and high sugar) possible causes of a stuck fermentation;
a) insufficient level of nitrogen or other nutrients
b) too high sugar concentration
c) high ethanol concentration )
d) too high temp(over 30 C due to exothermic ferment)
e) too low temp (less than 10 C)
f) some wild yeast strains (Hansenula, Pichia, and Saccharomyces) secrete proteins called killer toxins ( Mostt common ones K1 and K2)
There are three ways of stopping fermentation:
1-Racking: siphoning wine without disturbing the dead yeast (lees) which is collected at the bottom ) most common one. racked 2-3 times:
– once at the dryness
-tartarate removal (chilled to 0-2 C ( 4-10 days) to crystallize tartaric acid)
– after finning before filtration)
2-adding alcohol ( increasing alcohol concentration over 15 % will prevent yeast growth )
3–pasteurization by heat ( excessive flavor loss)
VII- Finning and clarification :
Finning: clarification of wine by the addition of a substance which reacts with tannins or proteins.the finning agent: adsorb suspended or colloidal material, the precipitate “settles out” of the wine .
– Agents used;
-gelatin-tannin,-casein,-bentonite ( a clay from volcanic ash deposition), -polyclar AT
Pectic enzymes ( chemical breakdown of the pectins): used as clarifying agent.
pectins act as protective colloids holding other constituents in suspension in the wine, giving the wine a cloudy appearance.
In most cases, pectic enzymes are used while the grapes are “fermented on the skin”, because higher yields during processing can be achieved
aging generally begins in relatively large upright tanks, which are usually made of stainless steel, redwood, oak or similar neutral materials.
– keep each cask or barrel filled to the brim.
– can turn into vinegar when in contact with air.
-The addition of wine to replace the wine loss by evaporation is called “topping” or “topping up”.
During aging , wine develops smoothness, mellowness and character.
some oxidation occurs as the wine “breathes” through the wood casks and the many complex natural elements of wine slowly interact, or “marry” for smoothness.
White seldom require aging more than 6-12 months.
Red wines mostly aged up to two years.
The smaller container: large surface/volume: wine can “breathe” and take on the flavor characteristics of the container.
VIII- Blending ( kupaj )wines for uniformity :
T have the same taste, color and fragrance in each bottle under a particular label( difficult to guarantee: sunshine, moisture vary from year to year. )
times to blend:
a)Blending different grapes while they are being crushed.
b)Young wines are blended soon after fermentation. c)Many wines of varying ages are blended after they are mature.
IX- Bottling wine:
Bottle when “ripe for bottling”.
If wine remains in wooden cooperage too long, it may take on an excessively woody flavor, loose character or especially with white wines, become over-oxidized.
wine is only beverage that continues to improve after bottling.
Closure for wine bottles are either corks, screw caps or combinations of both . Metal caps should have inner seals to provide tighter closing and to avoid chemical action of the wine upon the caps.
Seals or capsules are normally wrapped around the necks and mouths of wine bottles to close off leakage, discourage tempering and refilling and to enhance appearance.
Cork is the bark of the cork oak tree ,Quercus Suber, Western Mediterranean) Final product coated with paraffin and silicone
“Why does one bottle of wine cost twice as much as another same sized bottle of the same type of wine?”
-the grapes used maybe rare, delicate, hard to handle and expensive.
-aged for many years, -small quantity of the particular wine, -large enough demand
Vintage year ( the year grapes grown ) is very important for Europian wines because quality changes a lot year to year.
Classification of wines :
Dry wine ( no fermentable sugar left in wine)
Sweet wine ( some fermentable sugar exist in wine, either left or added after fermentation)
Fortified wine ( alcohol added )
Unfortified ( all alcohol from fermentation )
Sparkling wine ( fermented in the bottle )
Still wine ( fermentation is completed before bottling)
Evaluation of wines
a) Sensory examination:
-appearance ( clarity, and freedom from sediments )
-odor, aroma, bouquet
-Taste ( sourness, sweetness, bitterness, astringency caused by tannins)
-Flavor ( overall impression)
Sensory evaluation is important for determining when wine is ready for bottling or shipment.
b) Microbiological examination.
– microscopic inspection and plating. Its main purpose is to detect excessive numbers of spoilage bacteria and wild yeast.
A sample of wine is plated on the agar plate containing 100 mg/l cycloheximide. It is an antibiotic which inhibits wine yeast but not the wild yeast. So observation of growth on this plate will be indication of wild yeast contamination.
Due to existence of oxygen:
-ethanol to acetic acid (by acetic acid bacteria )
-it will oxidize the color of wine ( white wine amber color, red wine lawny brown color )
-flavor will also change(ethanol acetaldehyde)
Microbial spoilage : Look at handouts.
Spoilage by fungi rare most fungi are aerobic and sensitive to ethanol. ( important before and after the wine is made. ) contaminated cork closures: cork taints (2,4,6-trichloroanisole (TCA).
the most serious defects in bottled wine. (produce musty- or mushroom-smelling compounds )
Spoilage by yeasts
Kloeckera apiculata: cause a vinegar-like aroma
Brettanomyces/Dekkera: signature chemical for “Brett” spoilage is 4-ethyl phenol.
Spoilage by bacteria: the most common and most disastrous types.
Two distinct groups are of importance: the acetic acid bacteria and the lactic acid bacteria, both of which contain species able to tolerate the low pH, high ethanol conditions found in wine
Ropiness usually occurs only in
sweet wines and is caused by Pediococcus,
Oenococcus, and Leuconostoc spp. the formation of glucose-containing
polysaccharides, such as dextrins and glucans, can give an oily, viscous and objectionable mouth feel.
SOME IMPORTANT TYPE OF WINES
Vermouth : combination of wine, aromatic plants , sugar, sometimes grape must in limited quantities, and alcohol.
Caramel is the only coloring substance 15-20 % ethanol.
Dry ( <50 g sugar / l ,pale ) and sweet ( 150 g sugar / liter dark ).
neutral white wines + botanicals then distillation
Most popular appetizer wine ( 15-20 % alcohol). Fortified with spirit.
Development of flor yeast depends on the temperature, and wines should be stored between 15 and 20 °C The flor protects the wine from the uptake of oxygen, and prevents oxidative browning, to which the wine is very susceptible.
Characteristic nutty ( almond ) flavor is obtained by aging, 4-8 years, at worm temperatures with Saccharomyces beticus, S. montuliensis and S. rouxii ).
gassy beverages: the carbon dioxide is found in a state of oversaturation (generally, 4–6 bar at 20 °C, usually 2-3 times higher than soda pop).
When the wine is poured into a glass, CO2 is rapidly released as a result of the difference in pressure between the hermetically sealed bottle and atmospheric pressure.
two large groups:- natural sparkling wines (those produced by the Champenoise, Charmat method (or similar methods), or the ‘pearl’ wines, which have a natural ‘sparkle’)
-carbonated artificially (aerated sparkling wines).
Champagne ( sparkling wine ) :
Generally pale gold or straw colored. Clasiffied due to residual sugar content.
begins as a white table wine, usually several months old.
This wine is blended for consistent quality ( At this point it is called cuvee’).
Champagne yeast(strains of S. cerevisiae that are selected based on their ability to grow at high ethanol concentrations and low pH and temperature.) and sugar are added to cuvee’.
It develops more pressure than artificially carbonated soft drinks ever have, 100 psia at the end. ( secondary fermentation, 5-6 weeks, 11-12 C, then one year aging ).
After fermentation, the bottles may be transferred to a different site, for maturation at about 10°C.
Maturation lasts for 12 months;
0.1% SS corresponds to 5 psia.
sparkling wines require such thick heavy bottles , wired-on corks. Workers sometimes wear face masks and gloves.
Bottles of fermenting champagne are stacked in horizontal tiers or large boxes for few months to several years. During this time secondary fermentation occurs.
After its completion, the wine ages in the bottles and on the yeast , until the flavor and bouquet are perfected.
Champenoise , individual bottle process: ( Labeled as “fermented in this bottle”)
The bottles are placed upside down on racks. Each day the bottles are lifted slightly, twisted and turned , sediment has moved into the neck of the bottles.( riddling process)
The mouth of the bottles is plunged into a freezing solution of ethylene glycol (45%) or brine solution, freezing the wine and sediment in the neck.
When the crown cap is removed, the ice plug with the frozen sediment shoots out of the bottle due to the CO2 pressure. Pressure loss is approximately 1 bar, and wine loss is 10–15 ml. ( disgorging process).
To compensate for the wine lost in this disgorging process, clear champagne and the dosage ( which consist of a little sweet syrup and aged wine ) are added.
Finally the bottles are corked, the corks wired on and the bottle labeled.
The champagne undergoes a short final aging before shipment.
Charmat , Granvas or bulk method
Fermentation occur in Charmat tank.
Base wine and tirage ( nutrient, sugar and yeast) added.
The ideal temperature for fermentation is 12–13 °C.
When the desired CO2 pressure has been reached (approximately 4 bar), the temperature of the Charmat tank is reduced to 8 °C to arrest the fermentation (with 10% of residual sugars).
The low temperature causes the suspended yeast to sink to the bottom.
Filtration ( to another tank) by counter-pressure uses a gas (usually carbon dioxide)