ENOLOGY
Below is a brief explanation of each winemaking step used in RWM. For a more detailed description, please go to 'Resources' and follow Enology links. Please note that winemaking practices vary from one winemaker to the next. Below are steps borrowed from the Enology & Viticulture Department at University of California - Davis.
Enology, as defined by UC-Davis, is the study of wine and winemaking.
1. Red Wine Grape Varieties
• Merlot - Classic Bordeaux region grapes from France, requires less aging time, has softer tannins than Cabernet Sauvignon.
• Cabernet Sauvignon- King of the Red Wines, often blended with other Bordeaux varietal grapes. From DNA fingerprinting, it is a cross between Cabernet Franc (red grape) and Cabernet Blanc (white grape).
• Shiraz/Syrah - Grown throughout the world, demands a warm climate. Typical characteristics include white pepper, leather, wild gamey and intense dark berry flavors.
2. Crushing and Stemming
This step can be performed by hand or machine. When using a crusher-stemmer, two people can crush and stem 1 ton of grapes in about 1 hour.
The objective is to thoroughly crush the berries, recovering all of the skins and juice in the must (juice of pressed grapes), without macerating the seeds. Small pieces of stems and crushed seeds contribute to the wine's astringency (bitterness), thus at best, it should be avoided.
3. SO2 (Sulfur Dioxide) Adjustment in ppm (parts per million)
SO2 has been used in wine making for over a century. Adding a small amount will inhibit developments of molds, wild yeast, undesirable bacteria, rot and mold. It also prevents oxidation and browning.
According to recent research findings, the best quality wines are produced when sulfur dioxide is added before and after fermentation. Potassium metabisulfate (K2S2O5) is the common form used and available from most home wine making suppliers.
If the grapes are free of mildew, rot or mold - use 50 - 100 ppm per 10 gallons of juice or must. 75 ppm is the average. [75 ppm of SO2 is about 1/4 ounce - a little less than 1 level teaspoon]. Double it for grapes with rot, mold or that are broken.
Precautions: Be careful not to add too much SO2, as it can delay fermentation. Adding an excessive amount may hinder the process altogether.
4. Pure Wine Yeast Starter Cultures
Pure wine yeast starter cultures are added to promote alcoholic fermentation. For each 10 gallons of must, sprinkle two 5-gram packets of dry yeast pellets over the must. Two widely used strains are:
• Montrachet - Vigorous, has high SO2 tolerance. Avoid using this strain if you've sulfured the grapes a few weeks before harvest. This is to avoid production of hydrogen sulfite.
• Pasteur Champagne - Fairly vigorous, high SO2 and alcohol tolerance.
5. Alcoholic Fermentation
This is when grape sugars (glucose and fructose) are converted to ethyl alcohol (ethanol), carbon dioxide (gas form) and flavor components. Living yeast cells are the catalyst in this process.
Wines are traditionally classified according to their alcohol content. You can estimate the amount of alcohol with a known amount of sugar (measured in Brix).
Example: A given must or juice = 22.5 degrees Brix. Subtract 3.0 percent (nonsugar correction factor). You will yield 19.5 percent "true" sugar by weight. Then, multiply 19.5 by the specific gravity of 1.0803 to convert to percent. Then multiply by 0.59 and the approximate alcohol content will equal to 12.4 percent by volume. [Numbers are derived from charts offered by UC-Davis].
Energy in the form of heat is also produced at this stage. Thus, temperature is a factor, influencing the rate or each fermentation process. The amount of yeast inoculum and yeast nutrients also affect the rate of alcoholic fermentation. With red wine, it can take up to 2 weeks. These are the 3 stages:
1. 12 - 24 hours - Yeast cells grow, the must will bubble.
2. 36 - 48 hours - Yeast ferments one-half to two-thirds of the sugar to alcohol and CO2 gas. Fizzing and frothing will occur.
3. 70 - 80 hours - slow fermentation.
Recommended temperatures:
• 15.6 - 21.1C (60-70F) - to start with.
• 23.9 - 26.7C (75-80F) - proceed to this setting .
• 29.4C (85F) - allow it to rise for a day or more at this temperature.
• 20 - 21.1C (68-70F) - the remainder of the fermentation.
Precautions: Reaching or exceeding 32.2 - 35C (90 - 95F) can result in a stuck fermentation because yeast cells die at high temperatures. Also, fermentating for too long at above 29.4C (85F) can produce cooked odors and flavors.
6. Pressing
With a basket press or cheese cloth (wearing rubber gloves to avoid staining), extract the liquid portion and filter out the solids. This portion is called the free-run.
After you've gathered the free-run, you can add press-wine to it by applying pressure to the remains. Please note - adding too much press wine will result in higher tannin content, thus more bitterness, which will consequently require more aging.
* Press wine can also be kept for later, and added during the topping stage.
7. Malolactic Fermentation
Malic acid is an organic acid present in grapes and is stronger than lactic acid.
Soon after alcoholic fermentation, bacteria converts malic acid to lactic acid and carbon dioxide. This fermentation is accomplished by the activity of lactic acid bacteria, usually by species of the genus Leuconostoc .
The result is a reduction in acidity level. Therefore it is suitable for grapes grown in cooler regions and discouraged in warmer grape growing regions.
8. Racking or Siphoning
Racking or siphoning is carried out to clarify the wine. However, before racking, SO2 is added again (no more than 50ppm total SO2, if malolactic fermentation has not occurred and is desired). This is because the SO2 added initially has been exhausted at this point.
After making sulfite adjustments. racking proceeds. Racking is pretty much separating the lees (sediments) from the wine. An additional 4-5 rackings are performed every 4-6 weeks.
9. Topping, Oaking and Aging Ullage (evaporation) occurs as wine age, with losses at about 2 -5 percent volume (1 - 2 gallons per 50-gallon barrel per year. The ullage rate is related to temperature, humidity and the size of the barrel. Wine that is lost from evaporation must be replaced (topped) in order to prevent oxidation and growth of vinegar bacteria, which occurs due to presence of air and favorable conditions.
Red wines are commonly aged in oak barrels in order to extract woodiness and fine-tune the flavor and odor. Please keep in mind that newer oak barrels will impart wood flavors faster than older and used ones. An alternative to using oak barrels are add oak chips or pieces of oak to the wine.
Type of grape, size and age of barrel and desired results are all factors of aging duration. It can take anywhere from 6 months to more than 4 years.
10. Blending
Varietals are sometimes blended to fine-tune certain desired qualities such as color correction, acidity, tannins and oak levels. A common example is using Merlots to soften Cabernets since Merlots are lower in tannins.
References Cooke, George M., Lapsley, James T. Making Table Wine at Home [WWW] Available from: http://wineserver.ucdavis.edu/content.php?category=Winemaking [Accessed on 30 October 2006]. Cox, Jeff (1999) From Vines to Wines The Complete Guide to Growing Grapes and Making Your Own Wine. North Adams, MA: Storey Publishing.
Russian River Wine Road Inc. What is that Grape? [WWW] Available from: http://www.wineroad.com/wine101/grape.asp [Accessed on 30 October 2006].
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