Chapter 13

Bottling Wine

Pre-Bottling Wine Adjustments

The preparation of wines for bottling involves final filtration, analytical tests of chemical composition, microbiological stabilization, management of dissolved oxygen levels, and carbon dioxide adjustments. The preparation of blends, fining, stabilization, adjustments of acidity, and filtration should not be considered as finishing operations and will generally have been attended to some period before the time of bottling.

Filtration

Depth filtration is optimally effective if done within a 24- hour window prior to surface (i.e., membrane) filtration (Chapter 11). If not done within this time frame, the colloidal material in the filtrate begins to regroup and can cause surface clogging on the membrane. If longer than 24 hours, repeat the filtration through the same grade depth filtration media before filtering through the membrane. Alternatively consider using enzymes to mitigate other clogging factors (i.e., pectins and glucans).

Pre-Bottling Analysis

During a wine's lifespan, a number of parameters change. Common changes from juice to finished wine include removal of the sugars (glucose and fructose) by yeast fermentation, removal of malic acid in reds by bacterial fermentation (malolactic fermentation, MLF), production of ethanol from sugars, change in pH, production of lactic acid by malolactic fermentation, growth of spoilage organisms such as Brettanomyces bruxellensis (commonly referred to as Brett) and the addition of sulfur dioxide as an antioxidant and antibacterial agent.

Alcohol

Primarily due to taxation and labelling considerations, this parameter needs to be accurately known at the bottling and labelling stage of wine production.

Free and Total Sulfur Dioxide

As the major preservative used in wine, this is a critical parameter to check. The free sulfur dioxide level can decrease rapidly and is usually adjusted just prior to bottling so is normally measured then.

Glucose and Fructose

These major sugars can have a large impact on flavor and are the main food source for microbes but their concentration can easily change during the wine life cycle - knowing the accurate level at bottling is therefore considered important.

Malic Acid Concentration

While using paper chromatography to monitor malolactic fermentation is useful, it does not give an accurate reflection of residual malic acid concentration.

Microbial Stability

A wide range of wine faults can be caused by the growth of microorganisms in packaged wine some of which include gas/spritz, haze/deposit, volatility, oxidation, and reduced acidity (Chapter 16). The control of unwanted microorganisms at the time of packaging is therefore very important, so it's prudent to determine the microbiological status of a wine before bottling.

Residual Sugar

Any remaining sugar in the bottle, whether through an arrested fermentation or direct addition, can pose a risk for re-fermentation post-bottling.

Sulfur Dioxide

Bottling provides the last opportunity to adjust free sulfur dioxide to desired levels. Pre-bottling sulfur dioxide levels should be high enough to maintain adequate molecular sulfur dioxide after the bottling process. It is often reported that white wine should maintain a free sulfur dioxide content to achieve 0.8 ppm molecular sulfur dioxide based on wine pH with red wines being maintained at 0.6 ppm molecular relative to wine pH prior to bottling.

Volatile Acidity

The level of volatile acidity (VA) in wine is set by law and varies from country to country. For most states, with California as an exception, the maximum allowable VA for red wines is 1.40 g/L acetic acid (0.14 g/100 mL acetic acid) and for white wines is 1.20 g/L acetic acid (0.12 g/100 mL acetic acid).

Microbiological Stabilization

Typically, microorganisms are controlled by a combination of pH and sulfur dioxide and filtration. However, in the case of sweet wines, an additional treatment may be required due to the higher risk of refermentation if an infection occurs post-sterile filtration.

Sulfur Dioxide

The ability of sulfur dioxide to react with wine oxidants and prevent spoilage makes it indispensable in producing high-quality wines.

Sorbic Acid

Sorbic acid is exclusively used for the conservation of sweet wines to avoid their refermentation; it serves no purpose in dry wines (Section 18.7). The antimicrobial action of sorbic acid is primarily against yeasts and molds. It's action against bacteria appears to be selective. At concentrations used in wine it does not seem to prevent spoilage from either acetic or lactic acid bacteria.

Dimethyl-Carbonate

Dimethyl-carbonate (DMDC) is a sterilant sold under the trade name Velcorin used for yeast inhibition prior to bottling (Section 18.7). Dimethyl-carbonate is usually introduced into the wine on its way to the bottling line by a metering pump that can atomize the material into the wine.

Oxygen Management

Bottling is the last winemaking process during which dissolved oxygen can be added and have a significant negative impact on the aging potential and quality of wine being released to the consumer. Thus, extreme care must be employed in minimizing the amount of oxygen entry at bottling. Oxygen has the potential to dissolve into the wine at every stage of the bottling process. Temperature has an important effect on the oxygen level in wines. It is well known that decreasing wine temperature accelerates oxygen uptake.

Total Package Oxygen

Total package oxygen (TPO) management at bottling is crucial to avoid wine oxidation and is expressed as milligrams per liter (mg/L) or parts per million (ppm). Total package oxygen (TPO) is the sum of dissolved oxygen (DO) in the wine and headspace oxygen (HSO) contents.

Headspace Oxygen

After filling, oxygen in the headspace of the bottle is another source of oxygen absorption. This is due, in part, to the variability of the bottle headspace, which is influenced by such factors as, wine temperature, solubility of gases in the wine, bottle size, and closure. Headspace oxygen usually represents more than 50 percent of the TPO, which makes it the biggest reservoir of oxygen in a bottle. The oxygen trapped in the headspace has a higher partial pressure than the oxygen dissolved in the wine.

Measurement of Dissolved Oxygen

Measurements can be performed in real time using specific equipment for assessing oxygen at critical steps (transfer, filtration, bottling, and storage). These measurements can be performed directly on the transfer lines and in the bottles (dissolved oxygen in the wine and gaseous oxygen in the headspace).

Sparging

Prior to bottling, excess oxygen in wines can be removed by using an inline sparger (Section 17.4). This introduces an inert gas like nitrogen or carbon dioxide through a porous stainless-steel cylinder suspended in the wine. As the wine passes around the sparger, gas bubbles enter the product and displace the dissolved oxygen.

Sources of Dissolved Oxygen

Oxygen can dissolve into the wine at every stage of the bottling process, and it can have an effect on wine composition, shelf life, and consumer acceptance. During bottling, wine undergoes multiple operations: pumping, filtration, filling, and corking or capping.

Carbon Dioxide Adjustments

In certain cases, the carbon dioxide concentration must be increased; in others, it must be decreased. It can be increased by sparging with carbon dioxide; the gas can be injected in the winery piping. The same result can be obtained by placing wine in a partially filled tank, its headspace filled with mixture of a nitrogen and carbon dioxide.

Carbon Dioxide Levels

For each type of wine, there is a corresponding optimal concentration of carbon dioxide. Dry white wines tolerate higher carbon dioxide concentrations. If carbon dioxide levels in white wines are too low, the wine may be perceived as dull and flat.

Measuring Carbon Dioxide

Carbon dioxide analysis is performed before, during, and after bottling to document proper levels. Measuring carbon dioxide in the winery can be done a number of ways but the quickest and easiest of these is to use a Carbodoseur. This very simple device is a graduated glass cylinder with a screw top containing a long glass open-ended impinger tube.

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