葡萄酒酿造科学英文资料：Yeast issues part

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1、PROBLEMS WITH FERMENTSYeast Issues and References used for lectureWine Science - Jackson Chapter 7Wine Microbiology- Fugelsang Chapter 3Making Good Wine Rankine Chapter 6Pacific Rim Oenology Harvest 2010 Product listProducing a Healthy Fermentation Bruce Zoecklein, Virginia Tech http:/www.fst.vt.edu

2、/extension/enology/EN/105.htmlSwiegers, J. et al, (2005). Yeast and bacterial modulation of wine aroma and flavour. Australian Journal of Grape and Wine Research, 11, 2, Pages 139-173 http:/ H. et al, (2011) .Winemaking returning back to nature. Australian & New Zealand Grapegrower & Winemaker, 564,

3、 46-49. (moodle)Product Review: 2011. New frozen yeast released. Australian & New Zealand Grapegrower & Winemaker, 564, 53-54. moodle Product Review: Yeast NutrientsPhillips, C. (2007). What to Feed Your Fermentations . Wine Business Monthly, 07/15/2007http:/ impact does yeast have ?A diagrammatic r

4、epresentation of the microbial modulation of the profile of volatile compounds in wine (based upon Swiegers and Pretorius 2005). Wine yeasts and malolactic bacteria can produce desirable sensory results -by helping to extract compounds from the solids in grape must, -by modifying grape-derived molec

5、ules and -by producing flavour-active metabolites.The full picture.Formation of flavour-active compounds from sugar, amino acids and sulphur metabolism by wine yeast.Swiegers, J. et al, (2005). Yeast and bacterial modulation of wine aroma and flavour. Australian Journal of Grape and Wine Research, 1

6、1, 2, Pages 139-173 What some of the outputs contribute:See table 1 Sweigers et al, 2005Esters- from ferment influences fruity flavours. S cerevisiae strains produce a variable amount. E.g. isoamyl acetate, ethyl hexanoate, hexyl acetateMixed cultures of S. cer, Pichia sp. & Hanseniaspora sp increas

7、es acetate estersHigher Alcohols also called Fusel Excessive levels pungent 400mg/l e.gs harsh, spirit likeoptimal fruity Complexity 300mg/lProducts of ferment and alcohol breakdown- alcohol, acetaldehyde, acetic acid. Diacetyl also MLFGlycerolMajor product of ferment. Polyol- colourless, viscous, n

8、o odour. Can effect apparent sweetness of wineFallacy no relationship to tears. Only at very high conc (above normal) does it affect viscosityWhat some of the outputs contribute:MonoterpenesFormed during ferments by yeast or bacteria enzymatically release these bound up non-volatile precursorsGewrzt

9、raminer, Muscat , Riesling high levels of monoterpenesFaultsThiols potent grp of aroma compounds extraSome almost non-existent in grape juice result of ferment e.g. Combination. Furfury thiol ID ed in red Bordeaux and toasted oak staves Also roasted coffee, meat. Presence in wine from yeast transfor

10、mation of furfural in oakNon-volatile in juice e.g. in Sauvignon blanc bound to amino acid (cysteine)Yeast releases 4MMP- boxwood , 3MH, 3MHAExpression see handoutYeast choice new options (yesterdays hand out)New inoculated wild yeast strains1. Torulaspora delbrueckii (Prelude) pitched in with Sacch

11、aromyces sp.Reds enhanced red fruit and floral med chain fatty estersWhites SBL enhanced 3MH (3-mercapto hexanol)Increased palate weight for all wines more and fuller mouthfeelYeast choice new optionsNew inoculated wild yeast strains2. Pichia kluyveri again co fermented with Saccharomyces sp.Isolate

12、d in NZ. Enhancement of SBL characteristicsIncreases all thiols but esp 3MHAAlso elevates levels of mid chain fatty acid estersMid chain more stable than shorter molecules Claimed effects on wine: (Viniflora Frootzen)Increased fruit flavour intensity enhanced tropical fruit and citrus Larger spectru

13、m of fruit flavours, giving wines additional complexity Lower volatile acidity Rounder mouth-feelDesired Characteristics for a yeast1.Low foaming why?2.Low production of undesirables e.g?3. Ability to ferment to dryness - vigorous e.g. Premier curvee (1118). 4. Ability to be stopped if required - le

14、ss vigorous e.g. Epernay (Cote de blanc)5. Neutral fruit - dep on style - Sparkling e.g DV10, 1118Desired Characteristics6. Enhanced characters - colour e.g. W46, Bordeaux red- flavour & aroma (D47, RC212)7. Ability to flocculate rapidly - Sparkling and rapid turn around wines e.g. Lalvin 0168.Effic

15、ient conversion to Alcohol. (Not too much energy consumed by Yeast)9.Tolerate low temps - whites e.g M110. Tolerate SO2 - competition, control bacteria and wild yeastDesired Characteristics11. Even ferment short lag phase, even speed12.Tolerate high alcohol - restarts & hi alcoholUV43, L222613. Can

16、tolerate high fructose. To deal with hi F stuck ferments (e.g. Fermichamp)14. Has competitive factors (killer properties)What does “competitive factor” mean?KILLER!Wine yeast may contain proteins which allow them to prevent other yeasts from competing during the fermentation. Enables one strain to c

17、ompete successfully and dominate a ferment.Proteins are called Killer toxins, (K1 /K2)Wine yeasts can be killer positive (contain the toxin),killer sensitive (no toxin and are killed by the toxin) or killer neutral (no toxin and are not killed by the toxin).What does “competitive factor” mean?These

18、killer competitive factors are tiny proteins produced in the mitochondria of one yeast they move through the cell wall of the other yeast and upset Mg metabolism so the cell dies. All those factors in mindWhich yeast is right for the ferment?How can a winemaker go about selecting a certain yeast?Fir

19、stly:They can rely on past experience. Usually the best guide.But just because yeast performed well or in a desirable way for the winemaker one year, it will not mean that it will perform in a similar manner year after year. Why?Secondly:Seek advice from another winemaker. One in the same area, pote

20、ntially similar vineyardsRemember too . Their style aims may be different.Sharing info.How can a winemaker go about selecting a certain yeast?Thirdly:Seek information/advice from the yeast manufacturer or suppliers themselves.However, can a winemaker believe what is written on the packet or Fact she

21、et?And.Some times a winemaker has opposing needs and no strain is ideal. e.g. want vigorous ferment but also MLFJust have weigh up the options!Commonly used ! EC-1118Saccharomyces bayanusOriginThe EC-1118 strain was isolated, studied and selected from Champagne fermentations. Due to its competitive

22、factor and ability to ferment equally well over a wide temperature range, the EC-1118 is one of the most widely used yeasts in the world. Oenological properties and applications- extremely low production of foam, volatile acid and (H2S) - ferments well over a very wide temperature range, from 10 to

23、30C and demonstrates high osmotic and alcohol tolerance. - good flocculation with compact lees - relatively neutral flavour and aroma contribution.- Inhibits MLF and has strong killer properties.Recommended for all types of wines, including sparkling, and late harvest wines and dry whites. It may al

24、so be used to restart stuck fermentations.Final step : Yeast AcclimatisationInoculated ferments are only reliable if the yeast population added is optimalAim for at least 1 x106 cells per mlTo get that do (as we practice in the lab)1.Use the manufacturers recommendation rate (approx 2.5 g/l)2.Acclim

25、atise your yeast to juice temperatureTemperature shock kills great numbers of yeast cells. e.g adding a yeast culture at 40C to a must at 15C kills about the cell population!3.Pitch the yeast into your ferment (singing & encouragement optional!)Health of FermentImportant to have a healthy fermentSuf

26、ficient yeast to start with- (next terms lab)Rapid onsetSteady fermentSufficient resourcesNot excessive stressesAppropriate vigour yeastAcclimatise then pitch inpAnd encourage the yeast to: Phases of growthYeast growth - four phases but all of the phases may overlap in time: 1)the lag period,2)the e

27、xponential phase3)the stationary phase 4)the decline phase. Growth PhasesLag phaseImmediately following inoculation , cells adjusting to new environmentReproduction is the first great priorityMany die - so reproduction numbers = the number dyingWant a short lag phase - acclimatize wellCan be longer

28、if conditions are less than optimal- Low N2 - low pH can increase lag- 10C- little oxygen exposure at crushingExponentialRapid period of maximum and constant growthYeast cells dividing at regular intervals (their generation time).the population of viable cells rapidly increase to its maximum valueIn

29、 wine it is often a short phase 8 divisions. Large inoculum from either grapes or dry yeast- often about 106 cells/ml. Reaching 108 mlStationary phaseCommences when approx 1/3 sugar goneDepletion of nutrients or level of waste products now the rate of growth.The amount of cellular material remains c

30、onstant as cell division declines to approach cell death What is occurring?Ethanol toxicity disrupts glucose transportIncrease in toxic carboxylic acids that affect cell membranesStationary phaseAlso to help yeast surviveTrehalose (disaccharide) accumulates and stabilises membrane fluidity. Heat sho

31、ck proteins are produced as yeast gets stressed .limits protein denaturation Protection against oxidation is required - the blanketing CO2 provided by rapid fermentation is dissipating inert gasesSugars metabolized slowly during this and decline phase -up to 75% of the total ferment periodDeclineCon

32、centration of toxic metabolites increases- more cells die than divide.Not due to lack of food substrate! Increased membrane dysfunction becoming more lethal to cellular functionCombined effects of - ethanol glucose transport- mid-chain fatty (carboxylic) acid toxicity affects cell wall function - a

33、shortage in sterol precursors aid cell wall strength under tough conditions high alcohol conditions- absence of oxygenDeclineBecause most viable cells are not replaced, the colony eventually perishes, or becomes dormantLong in many wine fermentsUp to 40% of the sugar metabolized to alcohol during th

34、is phaseCells die slowly over the next few monthsGrowth Phases 1/3 sugar 75% ferment time 40% sugarMonitoring ferment important!Brix , Temperature and Taste every day!Getting ferments to go RIGHTHarvest Fruit condition Picked cool low temp (low oxidation)No diseaseNo MOGGetting ferments to go RIGHTS

35、O2-care not too much as can inhibit yeast & H2S So.As per the fruit condition requiresMachine harvested - may need 25-50ppm in field. - Plus further 25ppm at winery if condition bad (diseased)Hand harvested none in the field. Addition at the winery 25ppm 80ppm dep on condition of grapesGetting ferme

36、nts to go RIGHTYeastWhat the winemaker choosesDepends on style and needse.g. ?Brix, need for MLF?, wine style, temp of fermentTo avoid potential problems acclimatise! In your lab books!Practice in labs this weekGetting ferments to go RIGHTSupply sufficient food for the yeast to functionDetermine wha

37、t exists in the juice and the shortfall.1. Check YAN (yeast available nitrogen)YAN(ppm) = Ammonia (NH3)+ Alpha amino nitrogen (NOPA)Two enzymatic analysesYan guidelines 21Brix or less200-250ppm23Brix250-300ppm25Brix300-350ppmGetting ferments to go RIGHTReasons for higher nitrogen needsDiseased fruit

38、Dehydrated grapesHigh sugarHighly clarified juiceWild fermentHistory of vineyard with a sluggish fermentSo now you have determined your needsTiming of additions2.Add DAP and/or nutrients at intervalsAll at once = piggy yeast/kids candyAdditions spaced approximately as follows:1. Inoculation 2. 16 br

39、ix 3. 12brixTiming of additionsLate additions- below 10 Brix some say not effectiveOthers will still add butPotential problem increased ethyl carbamateFormed by the spontaneous reaction between urea and ethanol 2007 .WHO reclassified ethyl carbamate (urethane) Group 2A carcinogen - probably carcinog

40、enic to humans. In wine must be 15 ppb. Getting ferments to go RIGHT 3. What do we add?DAP Diammonium Phosphate (NH4)2HPO4 Nitrogen source. 21% nitrogenSuperfood - commercial preparationVitamins, minerals, DAP $Complex Nutrient supplements: purported to-Increase ferment predictability -Balance over

41、stimulation of yeast by DAP-Improve alcohol tolerance-Remove toxic by products e.g. short chain fatty acids-Reduce yeast stress - could cause acetic acid production-Allows more balanced aa uptake. Better aromas and flavoursGetting ferments to go RIGHTExamples:Cerevit. Mix vitamins -nicotinamide, cal

42、cium pantothenate, pyridoxine hydrochloride, thiamine hydrochloride and biotin. Add to deficient juice to max yeast numbers and activity. Yeast Hulls .Dried preparation of the cell wall membrane of whole yeast cellsAdditions (0.2 g/L) can - stimulate fermentation - Detoxification (soaks up poisons) Restarts- Supplies unsaturated fatty acids (C-16, C-18) acts as oxygen substitute and preventing deficiencies - Adds some amino acids and facilitates the release of CO2. Nutrition exercise see handout