Table Of Content

ask the Top tips for a successful yeast culture Vintage is here and it’s time to think cell population should increase to • The yeast culture should preferably yeast. To help you get the best out 100-200 million viable cells/mL of be slowly cooled to within 5-10°C of of your ferments this year, here are juice depending on the yeast strain the juice/must temperature before some common questions received at the chosen and the nutritional content inoculation; this amelioration awrI about yeast and some top tips for of the juice before cell growth stops process seems to be most important yeast rehydration. and the alcoholic fermentation begins. for difficult to ferment juices/musts. Healthy ferments should ideally • Cooling can be achieved by ARE ALL YEASTS THE SAME? have 1x108 cells/mL of must around sequentially adding appropriate There is a wide range of yeasts available halfway through fermentation. You can volumes of clean water or juice (with today for achieving a variety of wine check the total yeast cell number by low residual SO) from the tank to 2 styles, with most winemakers trialling microscopy using a haemocytometer. be inoculated over a period of 10-20 at least one new yeast each vintage. Cell viability, or the number of living minutes. Steps of 5-10°C are usual. Different yeasts can vary greatly in cells, is generally measured in a winery • When water alone is used, the yeast properties such as nitrogen demand; environment by viable staining using should be inoculated immediately production of hydrogen sulfide, sulfur a methylene blue dye. aim for >90% once the cooling steps have been dioxide, volatile acidity (Va) and viability. a value of less than 60-70% completed to avoid inactivation of glycerol; tolerance to sugar, alcohol, pH suggests there are issues with the the cells. If this is not possible, add and Va; and fermentation speed. For ferment. an equal volume of juice to the yeast example, in recent years, many people culture and inoculate within several have moved to using yeast with medium WATER AND JUICE hours and before the sugars become to high nitrogen demand. In these PARAMETERS depleted. Considerable foaming can, cases, the yeast assimilable nitrogen Hydration water should not contain however, result. Note that foaming is (YaN) level in grapes or must should be chlorine. Use mineral water/rain not an indicator of yeast viability. analysed, and adjustments made to suit water/clean tap water. Chlorine can yeast demand. It’s important to know be removed by sparging/boiling, or Step 3. Inoculation your yeasts and treat them accordingly. with sodium thiosulphate. ensure that • The juice/must temperature should grape juice has < 10 mg/L free SO / < equal or exceed 15°C when inoculated 2 WHAT IS THE RIGHT 30-50 total SO2 and does not contain to advantage the yeast culture over INOCULUM RATE? agrochemical residues. Do not add yeast indigenous strains. Different yeast suppliers and products at the crusher if also adding acid and • Active fermentation typically often specify different inoculum rates. SO2 for reds. Va in juice should be initiates within 24 hours. If not, Generally rates are between 20-40 g/ < 0.7 g/L. Bacteria and ‘wild’ yeast check the proportion of budding hL; some specify 25 g/hL. Following can produce Va and also deplete must and viable yeast by microscopic the manufacturer’s recommended rates nitrogen and vitamins. Check YaN examination. ensures a viable cell population > 5x106 levels in juice and adjust accordingly. • Once active fermentation begins, viable cells/mL of must. rates can be Consider the addition of proprietary the fermentation temperature can confusing as they are often expressed nutrients. be controlled within a small range. in different units. Here is an example Temperature changes exceeding conversion: 25 g/hL is equivalent to 25 YEAST HYDRATION PROCEDURE 3-5°C per day have been reported to g in 100 L or 250 g in 1000 L. It can also Step 1. Rehydration partially inactivate budding yeast. be expressed as 0.25 g/L or 250 mg/L. • Pre-heat water to 38-40°C For a 500 g packet, 250 mg/L equates to • Add water to a container with a BULK CULTURES adding one pack to a total tank volume large surface area. If using multiple with a successful hydration, yeast of 2000 L juice or must. packets you might want to consider cell walls will have incorporated using a large drum. sufficient growth factors to grow for VARIATIONS IN INOCULUM RATE • Rehydrate ADWY by sprinkling it about five generations under anaerobic For ferments predicted to be difficult, slowly and evenly over the surface of conditions. If scaling up a yeast culture high sugar musts, or highly clarified 5-10 times its weight in water (e.g. for tank to use to inoculate several tanks, white musts, a higher rate around 300 500 g packet of yeast by suspending keep for a maximum of 5 days to mg/L is recommended. Clarified musts in 2.5 to 5 L). maintain viability and purity of strain. will also require ferment nutrient and/ • Avoid formation of yeast clumps. It is also difficult to keep sterile culture or protectants such as sterol enriched Clumping results in non-rehydrated conditions for long periods so beware inactivated yeasts. For stuck ferments yeast, and hence, inactive yeast. keeping a culture more than 5 days as it is advisable to use double the normal Gentle stirring (do not use a powered other bugs can creep in. Use and top up rate or 500 mg/L. mechanical device, which can injure no more than three times during this the cells) can help disperse some time and don’t draw down more than WHAT IS THE IDEAL CELL strains that show water repellent 75% of the culture. NUMBER AND CELL VIABILITY? properties. rehydration of 250 mg/L active Dried • Leave to stand for 10-15 minutes. More information is available wine Yeast (aDwY) will achieve a on www.awri.com.au or, contact the minimum of 5x106 viable cells per Step 2. Amelioration AWRI Winemaking Services team at mL of must. This is based on aDwY • Mix the partially settled rehydrated [email protected] or 08 containing 2x1010 cell/gram. Initial yeast by stirring. 8313 6600. 42 Grapegrower & Winemaker www.winebiz.com.au January 2014 – Issue 600