Winemaking in the Classroom 2 Alcoholic Fermentation What

Winemaking in the Classroom 2 Alcoholic Fermentation

What is the primary objective? Making clean wine with an aim to bottling (giving to parents etc)? n No plan to bottle wine for drinking, making wine to test or investigate parameters? n Study of fermentation process only? n In all cases, aim for clean, complete fermentation to dryness n

Preparation of Fruit/Juice: If preparing from fresh fruit, crush or press fruit to separate gross solids/skins (do not puree!) n Some fruit should be peeled prior to pressing (citrus, apples, pears etc) n If making red wine from grapes – ferment on solids (crush only, don’t remove skins) n Can add 20 -30 mg/L SO 2 to prevent browning (optional) during settling n Suggest cold settling (<10˚ C) 24 -48 hrs to remove solids (protect from light and air) n Cold settling may be assisted by adding enzyme which will break down the pectins n

Preparation of Fruit/Juice (cont) If cold settled, rack off cold juice and discard heavy solids n Allow juice/must to warm back up to at least 15˚C n If SO 2 has been used (to prevent browning or clean up juice), check that FSO 2 is <20 mg/L n Consider adjusting sugar to 17 -22˚ Brix (9 -12˚ Baume) by adding table sugar (or diluting juice with water) as necessary n Adjust acidity to taste, ideally p. H between 3. 2 – 3. 6 (some fruits may be higher, p. H>4. 0 to be avoided) n

Treatment of Yeast n n n The viability of the yeast is the single most important factor to a successful fermentation Critical parameters are : correct culture preparation avoid temperature and/or mechanical shock (no vigorous mixing) ensuring that nutrient levels are adequate Always prepare a yeast culture (starter) – never add dry yeast to must/juice

Starting Fermentation - Culture n n n n Prepare culture: hydrate yeast at 35 o. C in 10 x vol water Stir very gently to wet yeast grains and leave to sit Add a little juice or sugar solution within 10 -15 minutes (juice must be within 5˚C of culture temp) Continue to add juice at regular intervals once yeast is active (note: fermentation will generate heat) Build culture up to 5% of final ferment volume Temperature difference between culture and juice <5°C before adding culture to bulk of juice/must Pour culture gently into top of must/juice in one motion Don’t mix or stir the culture into the must, it will gradually expand mix into the must as yeast growth occurs

Temperature Control n n n n n Temperature tolerance depends on yeast strain Too cold will inhibit or kill yeast (<10˚C) Too hot will ‘cook’ yeast (problems may start once temp >30˚C), plus ‘burnt’ flavours Ferment will generate considerable heat of its own, particularly in the first 3 -8 days Start ferments with cool musts (15˚C) If ‘cool store’ available (16 -18˚C) use it! Otherwise set air-conditioning to low in room In general white wines 14 -20°C, red wines 18 -27˚C Consider fermenting in winter!

Red Wine – Cap Immersion n n n For red (grape) wine, ferment on skins Colour and astringency from skins Skins will rise into a thick ‘cap’ on top of liquid Must keep immersing cap into liquid at regular intervals to aid extraction Don’t let cap dry out – spoilage can occur Leave solids in ferment 5 -10 days

Red wine - Dejuicing n n n n Around ⅔ to ¾ through ferment duration Usually assessed on taste Solids removed to avoid over-extraction of bitter compounds Lift cap off with a sieve or strainer Strain and press liquid through coarse stainless sieve into narrow-necked vessel and fit fermentation valve Note: don’t remove yeast solids that may have sunk to bottom – ensure they stay in ferment Discard skins and gross solids

Nutrient – What to add DAP – Diammonium Phosphate, inorganic source of nitrogen and phosphorus n DAP alone can be ineffective and may exacerbate VA production n DAP + Vitamin formulations – also supply essential B Vitamins and trace nutrients n Fermaid® – includes DAP, Mg. SO 4, yeast hulls, B vitamins – more ‘healthy’ supplement n Other similar ‘organic’ mixed nutrients ok too n

Nutrient – When to add If using highly clarified/filtered juice, add to juice prior to ferment n For ‘cloudy’ white juices, add once specific gravity has begun to drop (after lag phase) n For red wines on solids, may not need to add nutrient n Consider adding to reds if they get a bit smelly (hydrogen sulphide, rotton egg) n Nutrient added late in ferment is not very effective – add prior to 50% sugar depletion n

How long does fermentation take? n n n Anything from 7 days to 4 weeks Monitor sugar content daily using hydrometer (S. G. preferred) when S. G. reaches 1. 030, raise temperature by up to 5 o. C (to a max of 25 deg) Once S. G. near or under 1. 000, test for residual sugar using Clinitest® tablets, (not Clinistix ® ), Sugar must be under 20 gm/lt to use Clinitest (otherwise dilute into range) Benedict’s Test can also be used (same principle)

Observe your ferment regularly Smell, taste, think, check, style, structure, primary indicators n Bad smells can be a warning sign of undesirable side reactions n Consider addition of Diammonium Phosphate or other N supplement or B vitamin supplement to the ferment n Add nutrients pre 1. 040 SG to be effective n Don’t leave it indefinitely if nothing seems to be happening! n

‘Stuck’ fermentations n n n n Indicators are: SG flat-line – no change for 3+ days smell of bruised apples/sherry notes (indicates presence of excess acetaldehyde) Other smells that are unpleasant (H 2 S, ‘vegetable’ or ‘rubber’ smells, acetic smell) Most common causes are: Poor yeast culture preparation Initial S. G. >1. 100 – very high sugar must can cause alcohol stress in yeast Nutrient deficiencies

How to fix stuck ferments n n n n If temperature is <16 o. C and SG<1. 020 – raise temperature Add nutrients (‘Go-Ferm®’ or ‘Fermaid’®) (less effective late in ferment) Extreme solution: Rescue ferment – labour intensive Involves growing a fresh yeast culture up acclimatising it gradually to high alcohol environment by additions of wine from stuck ferment Increase addition volumes to fresh culture each day Combine with stuck ferment when new culture is 10% of ferment volume Pray…

When to call it quits…. n n n even when sugar remains…. ? depends on desired style to be achieved Keep in mind that an untrained palate probably won’t detect up to 10 gm/L residual sugar At 1 -1. 5 g/L reducing sugars, generally no fermentable sugar remains Safer to wait until sugar <2 g/L (Clinitest dark green/blue)

What next?

Stop ferment, add preservative n n n when sugar is @ dryness, or by desired sweet style cool vessel down – colder the better, to help stop yeast and encourage settling of dead yeast add SO 2 when cool – Camden tablets or Potassium Metabisulphite (PMS) salt aim for >35 mg/L Free SO 2 Consider that PMS is only 57% SO 2 At least 50% of added SO 2 will convert to bound SO 2

Post ferment clarification n n n Bentonite – clay mineral used for clarification 0. 25 gm/L dose in wine Make up as 5% slurry in water Make up day before use to allow swelling of particles Add to wine after SO 2 addition Rack clear wine 2 days after SO 2/bentonite addition

Racking n n n Separation of clear wine form settled solids (lees) Best to use a siphon with the end of the hose held above the lees Rack wine into a smaller container so that vessel is full Always keep wine vessels full unless fermenting This prevents spoilage due to oxidation or aerobic microbes

Safe wine storage n n n Full containers low dissolved oxygen Free SO 2 >35 mg/l @ p. H 3. 20 no fermentable sugars left Keep wine cool

Clarification and finishing n n n n Consider acid addition trial for flavour and balance Fining with bentonite for further clarification and protein stabilisation Check flavour, colour, bitterness, and structure first Other fining agents: PVPP, powdered milk, gelatine, isinglass - to alter or reduce bitterness/phenolics/tannins/low MW phenols. Cold stability: cool to -2 o. C - +2 o. C, add 3 gm/lt KHT, mix 1 hr, hold @ these temps, then earth or pad off lees within 24 hrs. Prevents tartrate precipitation in bottle Filtration options – depend on sweetness levels, persistant turbidity or clarity issues Earth or pad filter only after wine is protein and cold stable

Bottling Logistics n n n In industry we would check the following pre-bottling: p. H, titratable acidity, free and total SO 2, CO 2, H 2 S, alcohol content, flavour, colour, dissolved oxygen, protein (heat) stability, tartrate (cold) stability, residual sugar, turbidity/clarity, specific gravity Adjust Free SO 2 levels to 35 -40 mg/L Use clean, preferably sterilised bottles Fill bottles carefully with no splashing (avoid increasing dissolved oxygen) Seal with screwcaps, crown seals or corks