How fermentation works in Winemaking? (feat. Oray Wine) || Fermentation 101 || Wine Making

Fermentation is at the core of winemaking, changing grape juice into the wines we enjoy—whether it's a crisp white wine, the greatest red wine, or a bottle of joyous champagne. This natural process is powered by yeast, namely Saccharomyces cerevisiae, which transforms carbohydrates to alcohol and flavours. Winemakers frequently fine-tune the process by inoculating yeast and adding nutrients like di ammonium phosphate to guarantee a smooth and thorough fermentation. The aeration method can also help maintain the yeast healthy and prevent typical problems like slow fermentation and yeast infections. Whether you're interested in the science of fermentation or want to improve your craft, understanding these phases is critical to producing wines that truly shine.

Content:

1.       Activation of dry yeast (Rehydration Procedure)

2.       Yeast starter culture

3.       What is yeast assimilable nitrogen (YAN)

4.       Role of Diammonium phosphate (DAP)

5.       Aeration process

Activation of dry yeast (Rehydration procedure)

Yeast hydration recommendations might differ across vendors. In the first case, carefully follow the manufacturer's instructions as outlined on each yeast sachets. The suggestions provided here constitute a simplified generic yeast hydration approach that will improve the hydration and fermentation capacity of most Saccharomyces cerevisiae cultures. This general approach may not produce excellent results with non-Saccharomyces cerevisiae or other non-Saccharomyces cultures. Furthermore, specialised yeast reactivation preparations can increase yeast function when inoculating poor (very clarified/high °Brix/°Baume) juices or musts. For more precise information, contact your yeast supply or manufacturer.

Equipment and materials required

·         Water (Clean water/ RO water)

·         Yeast

·         Grape juice (No Preservatives)

·         Thermometer

·         Vessel with large surface for hydration 

Inoculation

Following the manufacturer's suggestions. The yeast producer has discovered the best method for rehydrating and activating a certain variety of dried yeast.

An inoculum of 0.25 g yeast/L (25 g/HL) juice is recommended to reach a minimum of 5×106 viable cells/ml. This is based on the ADWY which has 2×1010 cells/g. Because of their reduced liquid capacity, high solids musts are often infected with 0.20 g yeast/kg (approx. 20 g/HL).

For highly clarified juices, high °Brix/°Baume juices/musts, or musts with inhibitory residual SO2 (>10-15 mg/L free SO2 / >30-50 total SO2), a higher inoculum rate of up to double the standard rate is permitted. Oxidative procedures, including the use of hydrogen peroxide, can be employed to reduce excessive residual SO2.

Rehydration of Yeast

·         Pre-heat water at 35-40^oC; check the temperature properly by thermometer.

·         Add that water to the vessel.

·         Rehydrate ADWY by sprinkling it slowly and evenly over the surface of 5-10 times its weight in water (e.g. for 500 g sachet of yeast by suspending in 2.5 to 5 L).

·         Avoid forming yeast clumps. Clumping results in yeast that is neither wetted or rehydrated, and so inactive. Gentle stirring (do not use a powerful mechanical instrument, since this might harm the cells) can assist disseminate certain strains with hydrophobic qualities.

·         Allow to stand for 10-15 minutes.

Amelioration step

·         Stir the slightly settled, rehydrated yeast.

·         The yeast culture should be gradually chilled to within 5-10°C of the juice/must to be inoculated; this improvement procedure appears to be especially significant for difficult-to-ferment juices/musts.

·         Cooling can be accomplished by gradually adding adequate amounts of clean water or juice (with low residual SO2) from the tank to be infected over the course of 10-20 minutes. Steps of 5-10°C are common.

·         When using just water, the yeast should be injected promptly after the chilling processes are finished to minimise cell inactivation. If this is not feasible, add an equivalent amount of juice to the yeast culture and inoculate within a few hours, before the sugars diminish.

Inoculation

·         To give the yeast culture an edge over indigenous strains, the juice/must must be equal to or greater than 15°C when injected.

·         Active fermentation normally starts within 24 hours. If not, examine a juice/must sample under a microscope to determine the proportion of budding and live yeast cells. If these indices are low, a fresh yeast culture may need to be reinoculated.

·         Once active fermentation begins, the fermentation temperature can be adjusted within a narrow range. Temperature variations greater than 3-5°C per day have been shown to partly inactivate budding yeast.

Yeast should be stored precisely according to the manufacturer's guidelines, typically refrigerated; non-optimal storage conditions can result in activity loss, which might lead to unforeseen fermentation difficulties. Do not open yeast sachets between vintages. For difficult to ferment juices/musts, it is recommended to utilise fresh batches of yeast made using unique reactivation (inactivated yeast) preparations.

Yeast Starter Culture

To prepare your starter culture, make diluted juice:

·         Mix 1 litre of juice with 1 litre of chlorine-free water to make 2 litres of juice at about 15 degrees Brix. Use clean water. If there is any chlorine, remove it by boiling or sparging.

·         Maintain low SO₂ levels (≤ 5 mg/L free, ≤ 50 mg/L total). If it is too high, you can reduce it with hydrogen peroxide.

Sterilise everything.

·         Transfer the juice to a sterile 2 L container (such as a conical flask or bottle). Sterilise using heat, 70% alcohol, or 2% SO₂ solution.

Add Nutrients:

·         to keep the yeast happy, add 2 grammes per litre of diammonium phosphate (DAP) to the juice.

Inoculate with yeast:

·         Transfer yeast from the agar slope to the juice. Rinse the slope with about 5 mL of sterilised juice before adding it to the juice mixture.

·         Aerate with filtered air (50-100 mL/min) and keep the temperature between 20-25°C. Warmer temperatures equal quicker growth!

·         Check the yeast every 8 hours. Once it reaches ~2 × 10⁸ cells/mL, it is suitable for usage.

Barrel Inoculation

·         Gradually increase the temperature of the beginning culture to match the juice (no more than a 2°C variation per hour and a maximum 5°C difference at inoculation).

·         Use 2 L of starting culture per 200 L of juice for a solid inoculation rate of ~2 × 10⁶ cells/ml.

Scaling for large quantity

For ≤1,000 L of Juice:

·         Make more diluted juice at 15°Brix and modify the pH (3.1-3.4) and YAN (>180 mg/L) to maintain the yeast thriving.

·         Add the starting culture to larger volumes:
2 L culture plus 2 L juice equals 400 L batch.
2 L culture + 8 L juice equals 1,000 L batch.

·         Continue to aerate (250-500 mL air per minute) and keep an eye on the yeast. Inoculate when the concentration reaches around 2 × 10⁸ cells/ml.

For >1000L of juice:

·         Use a yeast propagator to expand in 10x increments (e.g., 2 L → 20 L → 200 L → 2,000 L). Each step takes 1-2 days, so plan ahead.

·         If necessary, cool the culture to ~5°C and continuously aerating to prevent yeast from settling.

Yeast Assimilable Nitrogen (YAN)

Nitrogen is essential for yeast development and good fermentation. It has an impact on fermentation pace, completeness, and the sensory profile of the wine, such as the development of fruity or reductive qualities. Yeast Assimilable Nitrogen (YAN) analysis allows winemakers to check nitrogen levels in grapes, musts, or juices and treat shortfalls with inorganic solutions such as di-ammonium phosphate (DAP) or organic yeast nutrients. Winemakers may improve the flavour character of their wines by efficiently regulating nitrogen levels. However, adding too much nitrogen, particularly from inorganic sources, raises the chance of ester taint development.

YAN is estimated by combining measurements of ammonia (NH₃) and alpha-amino nitrogen (αAN) utilising enzymatic tests, spectroscopy, or chromatography. YAN levels in Australia typically vary from 50 to 450 mg/L, with 100-200 mg/L being the most frequent. White wines normally require at least 150 mg/L of YAN, while red wines require at least 100 mg/L. Higher YAN levels (250-350 mg/L) are good for clean and fruity flavours, particularly in Chardonnay, but too much nitrogen might harm the wine's fragrance and leave residual nitrogen in the final product.

Sampling for YAN analysis is most successful when conducted close to harvest. Juice samples are recommended; however, pulp and skin samples may be more suitable for skin-contact cultivars. Samples should be obtained in cool to mild temperatures 1-2 weeks before harvest, excluding seeds. To guarantee reliable findings, samples sent for examination should be cleared and treated with sulphur dioxide. Nitrogen levels are carefully managed throughout the process to maintain optimal yeast vitality, consistent fermentation, and high-quality wine production.

Role of Di-ammonium Phosphate (DAP)

Di-ammonium phosphate (DAP) is essential for providing yeast with the nutrients it requires to flourish, particularly during the rehydration phase. Consider rehydration to be the yeast's "wake-up call" following dormancy—it's a critical period in which they prepare for the hard job of fermentation. Adding DAP during this stage provides yeast with a readily available source of nitrogen, which is required for the production of proteins, enzymes, and other cellular components necessary for growth and activity. Without sufficient nitrogen, yeast may struggle to operate, resulting in slow or even blocked fermentations.

Using DAP during rehydration also prepares yeast for a smoother start when it enters the must or juice. It reduces stress on the yeast, allowing them to remain robust and resilient in the face of demanding fermentation circumstances like as high sugar levels or cold temperatures. By ensuring that the yeast is well-nourished from the start, you not only improve fermentation efficiency but also assist to avoid the creation of off-flavors caused by stressed or underperforming yeast.

However, it's important to note that DAP should be taken with caution. Too much nitrogen might result in undesirable scents such as ester taints in the finished wine. So, it's important about striking the right balance—enough to nurture the yeast but not so much that the wine loses its flavour.

Aeration Process

Aeration is an important stage in winemaking that can improve the fermentation process and the overall quality of the wine. Winemakers may increase fermentation efficiency, minimise unwanted traits, and bring forth more brilliant flavours by gradually adding oxygen at important stages. Aeration in red wines helps create "red fruit" flavours, smoothes the taste by lowering astringency, and reduces off-putting reductive smells. It is essential for accelerating fermentation in white wines, especially in difficult batches.

Understanding the correct equipment and processes is essential for any winemaker wishing to experiment with aeration techniques. There are several ways to improve your winemaking process, from selecting the right equipment to knowing when and how to inject oxygen. Many wineries, regardless of size, have found success in using these principles, honing their craft, and producing greater outcomes in flavour and style.

To understand more about aeration and how to use it in winemaking, check read my blog post, Introducing Oxygen to Your Wine Fermentation. It includes everything from basic advice to sophisticated insights that will help you master this critical practice.

To summarise, fermentation is the core of winemaking, converting grape juice into the wines we know and love. Understanding the role of yeast—specifically Saccharomyces cerevisiae—is critical for making the greatest red wine, crisp white wine, or even champagne. Yeast inoculation, adequate nutrient utilisation (such as di ammonium phosphate), and the aeration process all contribute to a smooth fermentation trip. Paying attention to these factors not only avoids yeast infections, but also improves the taste and quality of your wine. By mastering these components, you may improve your winemaking talents and produce wines that are genuinely unique. Cheers to discovering the fascinating realm of fermentation—your path to creating excellent wines!

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