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Here you will find information about the process and equipment for making various types of wine.  This section will continue to grow, so check back often.  Choose your area of interest below:

Basic Concept Commercial Equipment
Red Wine Process White Wine Process
Hydrometer Stopping Fermentation
Fermentation & Temperature

THE BASIC CONCEPT OF WINEMAKING

Conceptually, winemaking is quite simple. You combine a flavoured juice with sugar, acid, tannin, and yeast, remove any pectin present, and allow the yeast to do what it naturally does with as little exposure to air and contaminates as possible. When the yeast is done, the result is wine. Conceptually, that's all there is to it. In reality, it's a bit more involved. There are subtleties to consider -- like proportions, for example, and dead yeast cells, pectin haze, suspended particulants, and a host of other things. Still, it's a simple concept.

We say that a wine's base is that from which the primary flavour of the wine is derived. Usually, that base is a fruit. In nature, there is only one fruit which provides all the required ingredients for making wine, and that's the grape. The grape has (or can have) the right amount of natural sugar, the right amount of natural acids, it's own flavour and tannin, and it hasn't got any pesty pectin. Best of all, it even comes with its own yeast. That powdery coating covering grapes is wild yeast, and it is sufficient to start and finish fermentation. Not all grapes, however, are created equal. Some will have an abundance of natural sugar and some will be deficient. Some wild yeasts will carry fermentation to 10% alcohol before the alcohol kills them off, but some will only get to 6%. Some have lots of tannin -- too much, really -- and some will fall short. Still -- and we are still speaking conceptually -- the grape is the perfect winemaking base. All others fall short in one aspect or several. In essence, then, the "art" of making wine is to optimize the various aspects in order to make great wine.

The various aspects to be optimized depend on what kind of wine one is making and the quality of the various ingredients.

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COMMERCIAL WINE MAKING EQUIPMENT

Here is a list of the commercial equipment used for making red or white wine. The size of the equipment varies based on the amount of grapes being processed.

1) Variable Capacity Tank (1,000lt to 8,000lt)
2) Grape Destemmer Machine
3) External Flexible Impeller Must Pump
4) Vertical Basket Press or Membrane Press
5) 20 Plate and Frame Filter with 40cm Pads
6) Semi-Auto Filter, Corker, Spinner and Pressure-Sensitive Labeller in one

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THE RED WINE PROCESS

Black arrows indicate critical stages; blue arrows indicated optional ones

Crushing

The old way was to tread the grapes: the modern way is to crush and then destem them with mechanical crusher-destemmers. The aim of crushing is to split the skins and release the juice, enabling yeast activity and fermentation to begin. Destemming is not always necessary and bunches may be crushed whole, but stems and stalks are usually removed if the winemaker wishes to avoid high tannin levels in the wine.

First Fermentation & Maceration

Fermentation vats were traditionally made of oak. Many still are, but stainless steel has the advantages of being easier to clean. High uncontrolled fermentation temperatures burn out the fruit flavours in the wine but can also promote greater colour extraction from grape skins, so a good temperature balance is essential. The length of maceration, the period during which the juice is left in the vat in contact with the grape skins, depends on the depth of colour and tannin required in the wine. Not so long ago workers would get into the vat to break up and submerge the cap of skins.

Carbonic Maceration

Carbonic maceration is an alternative fermentation process in which the fruit is allowed to ferment spontaneously under a protective layer of CO2. This weight of the grapes is sufficient to crush the fruit and release the juice, known as free-run, without mechanical pressure. The resulting wines tend to be softer and less astringent than those fermented in the traditional way, so this method is well suited to grapes which normally give hard, acidic wines. Wines made by carbonic maceration are usually for drinking young (or example, Beaujolais Nouveau) and do not respond well to aging.

Pressing

Pressing the grape mass, or pomace, occurs after the free-run wine has been removed from the fermentation vat. This process is not for white, and in fact is not always carried out at all. 'Press wine' is high in tannin and colouring pigments. At the discretion of the winemaker a percentage of it may be blended with the free-run wine to add tannins, character and longetivity.

Malolactic Fermentation

This process is almost always encouraged in red winemaking. It is a secondary fermentation in which malic acid is converted into lactic acid and CO2. It softens the acidity of the wine and, once complete, adds to its complexity and stability.

In many European cellars the wines will mature for six months before the malolactic fermentation commences (in the spring following vintage).

Maturing

Maturing in Oak

High quality red wines today are almost always matured in oak. Oak contributes vanilla and wood tannin flavours. For how long the winemaker ages the wine in barrel is one of the crucial decisions, arrived at by regular tasting.

Racking

The wine is racked every few months by transferring it to a clean sterile barrel, gently aerating it and leaving any sediment in the bottom of the old barrel.

Fining

The object of fining is to clarify the wine. The fining agent (usually egg white or bentonite clay) is poured onto the surface. As it sinks through the wine it carries any solids to the bottom of the vat.

Filtration

The final option before bottling is whether or not to filter. Passing the wine through a fine filter guarantees (or should guarantee) its stability and 'brightness' even under fairly adverse conditions. But some winemakers believe it strips the wine of its character.

Finishing

Before bottling the wine should be completely stable. It remains vulnerable to oxidation and contamination until the cork goes in. Mechanical bottling lines account for 95 percent of modern bottling. It is important to fill the bottles to exactly the right level to allow adequate room for the cork.

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MAKING WHITE WINE

Black arrows indicate critical stages; blue arrows indicated optional ones

Crushing

The first stage of controlled vinification is to crush the grapes and release the pulp and juice, making them easier to press. A Key decision at this stage is whether or not to remove the stems. Left with the grape stems allow juice to drain more freely during pressing. For some wines, where white wines are being made from red grapes, crushing of any kind is avoided (because it would colour the wine): grapes go whole into the press.

Pressing

Cooling

Delaying fermentation until after pressing is essential. Where the ambient must temperatures are high the juice is cooled by pumping it through 'must chillers'.

Pressing

White wine grapes are always pressed. Better quality juice results when pressing is gentle. If too aggressive the pips and stems break and bitter astringent flavours, which overpower those natural in the grapes, are released. Good results are achieved with pneumatic presses, which are now replacing traditional vertical wooden ones. Both types yield juice of the highest quality and also enable the separation of different quality pressings.

Settling

The juice is drained from the press into settling vats where the skin, pip and stem fragments remaining in suspension after pressing will settle to the bottom of the vat. The clean juice is then racked into separate vats ready for fermentation to begin. Centrifuging can also be carried out at this stage to clarify the wine, but it is an aggressive process, removing all the larger particles in the must, even yeast cells. It is often carried out when cultured yeasts are to replace natural ones for fermentation.

Fermentation

Traditionally in oak casks (increasingly favoured for many high quality wines) white wine is now more often fermented in stainless steel vats which enable easier regulation of yeast activity through temperature control. Prolonged fermentation at cool temperatures protects primary fruit characteristics and ensures the conversion of all the sugar to alcohol. After fermentation some winemakers chose to leave their wine in contact with its lees (yeast sediment) which adds both flavour and freshness to the wine, retained by bottling it without delay.

Malolactic Fermentation

To soften astringent acidic flavours and to add complexity, a second or malolactic fermentation can be encouraged (it may occur quite naturally or be brought about artificially). This converts harsher malic acids to softer lactic ones. Where retaining acidic qualities in the wine is important (eg in warmer climates where the grapes gain greater sugar and fruit flavours at the expense of their natural acidity) this second fermentation is prevented by removing the yeasts and proteins needed to initiate it.

Maturing

Clarification

Filtration, centrifuging or fining with bentonite clay (which 'collects' remaining yeasts, proteins, grape skin particles etc, and precipitates them to the bottom of the vat) are used to prevent unwanted malolactic fermentation and any further yeast activity once all the sugar in the wine has been converted to alcohol It also removes substances leading to 'off tastes'. With clarification the wine gains stability: the processes used for this stabilization, however are quite aggressive and many believe they lead to flavour loss. Clarification is completed by removing tartrates from the wine. Modern wineries now use thickly insulated stainless steel vats for cold stabilization. By cooling the wine to around - 4C, tartrate crystals, which may otherwise form in the bottle, precipitate and fall to the bottom of the vat. In Germany this process traditionally occurred in large oak Fuders situated in cellars cool enough for tartrates to precipitate out at ambient temperatures. After stabilization the wine may be bottled immediately or matured first in oak barrels.

Maturing in Oak

Maturing white wine in new oak imparts flavours which can overpower wines of more subtle character, but add depth and complexity to others. Older barrels give more moderate flavours and are an option often favoured in Burgundy.

Finishing

Bottling

During bottling cleanliness is essential: any bacterial activity, which may be encouraged by warm temperatures- especially when the wine is later transported or shipped for sale- is prevented by passing the wine through a fine filter. Some producers bottle the wine straight from its lees after fermentation to retain yeast character and freshness (even a slight spritz). Others, particularly in the New World, inject CO2 at the bottling stage for the same effect.
 

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THE HYDROMETER

You use a Hydrometer which, is to the winemaker what the compass is to the mariner. The proper use of the hydrometer allows you to guide your activities precisely from pre-fermented must to final perfection and to discern all the steps in between.

The hydrometer is a simple instrument that measures the weight--or gravity--of a liquid in relation to the weight of water. Because the relation of the gravity to water is specified, the resulting measure is called a specific gravity. A hydrometer will float higher in a heavy liquid, such as one with a quantity of sugar dissolved in it, and lower in a light liquid, such as water or alcohol. In truth, you do not need to have an interest in the specific gravity of a must per se, but you do need a very keen interest in the amount of sugar dissolved in it, for yeast converts sugar into carbon dioxide and alcohol. By knowing how much sugar you started with and ended with, you can easily calculate the resulting alcohol.

There are many variants of the hydrometer. Some have only one scale, some two and some three. The typical hydrometer measures three things: specific gravity (S.G.), potential alcohol (P.A.), and sugar.

The specific gravity scale will usually read from 0.990 to 1.120. The S.G. of water is 1.000. If you fill a test jar (a deep chimney-shaped vessel that holds from 1/2 to two cups of juice) with water and float your hydrometer in it, the water surface should rest at the 1.000 mark. As you dissolve sugar in the water, the hydrometer will float higher. One pound of sugar dissolved in one U.S. gallon* of water will float the hydrometer to the 1.045 level.**

One U.S. gallon equals 128 fluid ounces, or 3.7853 litres, or 0.833 Imperial gallons, while one Imperial gallon equals 160 fluid ounces, or 4.5459 litres, or 1.2 U.S. gallons and five U.S. gallons equals four and one-sixth Imperial gallons, and five Imperial gallons equals six U.S. gallons.

The potential alcohol scale typically reads from 0 to 16%. Using the standard hydrometer, you cannot measure the alcohol in a finished wine. But you can measure the P.A. before the yeast is added and measure it again after fermentation is complete. By simple subtraction, the P.A. lost is the percentage of alcohol in the finished wine.

Accurate alcohol content cannot be calculated using a hydrometer alone because the actual S.G. of pure alcohol is 0.792, not 0.990 as most hydrometers read. However, if you accurately measured your must's S.G. before yeast was introduced and fermented it to an S.G. of 0.990, racking as required, your calculation should be accurate to 1%.

 

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STOPPING FERMENTATION

Unfortunately, there is really no practical way to successfully stop fermentation before it is ready to stop on its own.

If you are looking to stop the fermentation to preserve the current level of sweetness you will need to let the wine finish fermenting completely to where it is dry. Then let the yeast settle out to the bottom on its own over a 2 to 3 week period.

Once this happens you can then siphon the wine off of the yeast settlings and add Potassium Sorbate and Sodium Bisulfite as directed on their packages and then simply sweeten your wine to taste with a sugar mixture of your choice.

 

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FERMENTATION & TEMPERATURE

When fermenting at low temperature you need to increase inoculum. For uncontrolled high temperature you need to decrease inoculum slightly and select a slower fermenting strain of yeast. Around 250-500 mg of yeast nutrient/L must is also needed to protect the yeast at each end of the temperature range.

With yeast preparation be sure the hydration of fresh culture in warm water is exactly at the supplier's stated temperature as this is critical for maximum viability. A large percentage of the cells die if rehydration is done at cooler or warmer temperatures. After rehydration the yeast should be added to the must within 20-30 minutes or a source of sugar should be added to the culture. If this is not done, cells go into a premature decline phase resulting in an inoculum of low cell concentration.

Also, it is imperative that you avoid temperature shock (no more than 5-7 C differential between culture and must temperature) as temperature shock kills great numbers of yeast cells. For example, adding yeast to a must at 60 F/ 15 C kills about half the cell population.

With barrel fermentation there are a number of considerations that can influence aroma and flavor, like the fermentation temperature as well as barrel pretreatment, the age of the barrels, the timing of the fill, and whether the fermentation is produced by yeast only or by a mixed culture.

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