Ch. 13: General Winemaking Options

Question 1

Oxidation

Answer 1

Exposure to oxygen has a significant effect on wine style and quality. The effects can be positive or negative depending on the wine style, grape varietal, timing and amount of exposure.

The general effects of oxygen exposure are a loss of fruitiness, aromas of nuttiness or apple which may or may not be desired, gold or brown colors in white wine.

Phenolic compounds in red wine have an anti-oxidative effect, and so can tolerate higher amounts of oxygen.

Lack of enough oxygen in winemaking and storage can lead to overly reductive aromas, which are considered to be wine faults.

Controlled exposure to oxygen can be positive to many wines. In red winemaking, oxygen stabilizes color, adds complexity (aromas such as mushroom, leather, toffee, coffee, and dried fruits).

Oxygen promotes yeast and bacterial growth, so needs to be monitored carefully.

Question 2

Sulfur dioxide

Answer 2

A preservative that can be applied in gas, liquid, or solid form, and is regulated by law as it is considered a toxic substance. The term sulfites needs to be added to a wine label if the wine contains over 10mg /L.

It is generally added to the grapes after they are picked, and may then be added at various times in the winemaking process and usually at bottling.

The timing and amount of SO2 determines its effectiveness. For example, adding larger amounts when the grapes are crushed, at the end of MLF, and at bottling is more effective than adding small amounts throughout the winemaking process.

While sensible amounts are often necessary to prevent faulty wine, too much SO2 can dull the flavors.

Question 3

anti-oxidant

Answer 3

Reduces the effect of oxidation by reacting to oxidative outputs and inhibiting oxidative enzymes.

Question 4

anti-microbial

Answer 4

Inhibits the development of microbes such as yeast and bacteria.

Question 5

Bound SO2

Answer 5

The portion of SO2 that reacts to the compounds in the liquid. It is ineffective against oxidation and microbes.

Question 6

Free SO2

Answer 6

The proportion of SO2 that is not bound. Most of the free SO2 is inactive and a small proportion is molecular CO2, the most effective against oxidation and microbes.

Question 7

Grape Transport

Answer 7

Grapes are vulnerable to microbial infection and oxidation when transported to the winery. Hot temperatures increase these risks, so wineries will try and pick when the weather is cooler, or at night. Red grapes are less vulnerable to oxidation due to phenolic compounds, which act as antioxidants.

Other protective measures include adding SO2 (which has antioxidant and antimicrobial properties), Putting grapes in cold storage at the winery, sanitizing harvesting equipment, and collecting and transporting grapes in small crates to minimize crushing.

Question 8

Grape Reception

Answer 8

On arrival to the winery, the reception of grapes will depend on the volume, Whether they were hand or machine harvested, and the quality of the grapes.

large volumes of grapes that have been machine harvested are usually transported on a conveyer, while hand-harvested grapes are transported in smaller crates, on forklifts or by hand.

The grapes are transported either to the sorting phase or to the destemmer/crusher.

Question 9

Chilling

Answer 9

I the grapes are warm when they reach the winery, they are more at risk from oxidation and spoiling. Therefore, the winemaker may choose to chill the grapes before crushing. Chilling can also help preserve fruity aromas, so is especially helpful for fruit-forward wine styles.

There are two ways to chill grapes: refrigeration and a heat exchanges.

Refrigeration is used for whole bunches of grapes and takes place in a refrigeration unit. It takes time, which may slow processing.

For destemmed or partially crushed grapes, the grapes can be run through a heat exchanger, which is a much faster process.

Both incur costs, which can be reduced by picking the grapes when it’s cooler, or at night.

Question 10

Sorting

Answer 10

The level of grape sorting, or whether sorting will be done at all is dependent on the quality of the grapes, the intended final quality and price, ripeness and health of the fruit, and whether any sorting was done in the vineyard.

Sorting adds costs of labor and time, so for inexpensive wines, likely won’t be done. In poor years or in cool climates, however, a certain level of sorting may be required to remove moldy and underripe grapes.

MOG (material other than grapes) includes twigs, insects, and leaves, may still need to be removed in good years when the grapes are in perfect condition.

Question 11

Optical sorting

Answer 11

A high tech, high cost option for sorting which uses digital imaging and software to scan individual grapes. Any grapes that don’t conform to the winemakers sample, as well as any MOG, are removed.

Due to the high cost of the machine and high level of selection, this option is only used for premium and super premium wines.

Question 12

Destemming

Answer 12

Destemming is automatic for machine-harvested wines as the grapes are shaken from the stems during harvesting. For hand-picked grapes, the destemming is done at the winery. It is done for most white wines and some red wines, as the stems contribute tannins to the wine, undesireable for whites, but desireable for some red wine styles.

If stems are included for the final wine, It is important that they are ripe so as not to impart green, bitter tannins to the wine.

There are some wine varietals and styles that are not destemmed. These include wines where the grapes are fermented as whole clusters, usually Pinot Noir and Burgundy. Wines that are made using carbonic maceration, such as Beaujolais, and wines that are made from grapes that are pressed whole-cluster, like sparking wines.

Question 13

Crushing

Answer 13

Crushing happens at the beginning of the winemaking process, and involves gently crushing the grapes to break the skins and release the juices. It is important not to crush the seeds, as this will impart bitterness to the wine.

Crushing releases the must, which is is a mixture of the juice, pulp, seeds, and skin, or in the case of white wine, the juice.

Question 14

Must

Answer 14

The substance that is being fermented. Typically, in red wines, this includes the juice, pulp, seeds, and skin. In white wines, it is the juice.

Question 15

Pressing

Answer 15

In white wines, pressing takes place before fermentation to remove the skins and seeds which contain tannins and are not desirable in white wine.

In red wine, pressing takes place after after either soaking the juice with the seeds, skin and possible, stems for a chosen amount of time by the winemaker, or after fermentation, depending on the wine style. The skin and seeds impart desirable characteristics to red wines.

In both cases, pressing is done gently enough so that to maximize the release of juice without extracting too many tannins and bitterness from the skins and seeds.

Question 16

Pneumatic press

Answer 16

A cylindrical cage where wine is entered on one side of the cylinder, and compressed air into the bladder. The grapes are gently pressed against the cage, separating the juice and wine from the skins.

Advantages are that the winemaker can control the amount of pressure and extraction, depending on the style and varietal. It can be flushed with inert gas to protect the juice or wine from oxidation. They are common in medium to large scale wineries that can afford the initial investment.

Question 17

Basket press

Answer 17

These are ‘baskets’ in which the grapes are placed, and pressure is exerted from above. The juice or wine runs through gaps in the side of the basket, and is collected in a tray along the bottom and is transferred into another container via pipes. Gentler than Pneumatic, good for sparkling. More suitable for whole bunch pressing.

It generally holds a smaller loads of grapes, lower yields, and is not sealed, so cannot be flushed with inert gas to protect against oxygen. It is also much more labor intensive. These factors make it more suitable for small, premium wineries.

Question 18

Horizontal screw press

Answer 18

Similar to a basket press, though less gentle, and therefore, less popular. The press is mounted horizontally above a tray.

Question 19

Continuous press

Answer 19

Unlike other pressing methods which require grapes to be added to the press in batches, the continuous press adds large volumes of grapes continuously. This allows for quicker pressing of large volumes of grapes, but is less gentle than other methods. It is mostly use for large-volume, inexpensive wines.

Question 20

Must adjustments

Answer 20

Winemakers can make adjustments to the must in order to create balance in the final wine when conditions are less than ideal, and the grapes do not have the right amounts of sugar, acid, tannins or flavors for the desired wine style.

Adjustments include enrichment (increasing alcohol levels), reducing alcohol, acidification, deacidification, and adding tannins.

Question 21

Enrichment

Answer 21

Increases the alcoholic content of the final wine, and is commonly used in cool climates before or during fermentation. It refers to a range of practices, including adding sugar to the must in the form of dry sugar, grape must, or RCGM (rectified concentrated grape must), and concentrating the must through reverse osmosis, vacuum extraction, or chilling.

Adding dry sugar in the form of either beet or cane sugar is called chaptalization, and is a common practice.

Another way to enrich the must is by removing water and concentrating the must. This can be done through technological process such as reverse osmosis, vacuum evaporation, or freezing the must and removing the ice. These methods add cost in the form of initial outlay for the equipment and less wine volume.

Question 22

Acidification

Answer 22

The process of increasing acid in the must. This is typically done in warm climates where acid levels drop dramatically as the grapes ripen, and with tartaric acid, although other acids can also be used (malic, citrus, and lactic).

Acidification can happen before, during, or after fermentation, but is generally preferred before fermentation in order to benefit from low pH levels (increase in microbiological stability and SO2 effectiveness), and because it integrates better with the final wine.

Like enrichment, acidifaction is restricted in the EU according to climactic bands.

Question 23

Deacidification

Answer 23

The process of lowering the acid in the must or wine. When considering deacidification, malolactic conversion must also be taken into account as it will contribute to the acid levels of the final wine.

Deacidifaction is carried out by adding calcium carbonate or potassium carbonate, which lower acidity by the formation of tartrates. A high-tech option is also available through ion exchange, but requires a considerable upfront cost for the equipment.

Question 24

Yeast

Answer 24

Yeasts are microscopic fungi which convert sugar into alcohol and affect the aromas and flavors of wine. In order to do this successfully, yeasts need adequate temperatures, nutrients (especially nitrogen), and the absence of oxygen. Oxygen is needed at the beginning of the fermentation process to multiply the yeasts, but once the oxygen is used up, fermentation begins.

Besides, alcohol, CO2, and heat, other elements that are released during fermentation include aromas (both via aroma precursors and the yeasts themselves), glycerol, and volatile acidity.

Question 25

Saccharomyces cerevisiae

Answer 25

The most commonly used yeast in winemaking. It can withstand high acid levels, high alcohol levels as the must ferments, and therefore, can reliably ferment the must to dryness. It also is mostly resistant to SO2.

Question 26

Ambient yeast

Answer 26

These are yeasts found in the the vineyard and winery (or wild yeasts). It will include a range of yeast species that will quickly die out once the alcohol reaches 5%, so the dominant yeast that remains is usually Saccharomyces cerevisiae.

Advantages are that they are free, can add complexity and aroma compounds, can create unique flavors and aromas particular to the vineyard, can be used in the marketing of wine.

Disadvantages are that fermentation may be slower, leading to the build-up of volatile acids, spoilage organisms, and bacteria, leading to off flavors. An increased risk of stuck fermentation, and lack of consistency.

Question 27

Cultured yeast

Answer 27

Sometimes called commercial yeasts, are yeast strains that have been selected and grown in a lab, and are usually strains of Saccharomyces cerevisiae.

Advantages include reliable, fast fermentation to dryness; lower levels of volatility and decreased risk of spoilage; consistency in the final wine; and control of the flavors and aromas of the final wine by using specific yeast strains to produce desired effects. For example, neutral yeast strains may be used for sparkling wines while other strains may be used to boost the desired aromas of a dry white wine like Sauvignon Blanc.

Disadvantages include the claim that cultured yeasts create a sameness in wine flavors, and the added costs.

Question 28

Malolactic Conversion

Answer 28

The process of converting malic acid to lactic acid by lactic acid bacteria. It also creates CO2 and warmth.

Ideal conditions include warm temperatures (74 - 72 F), moderate pH levels (3.3-3.5), and low levels of SO2. The opposite conditions (temperatures under 59 degrees F, low pH and moderate levels of SO2) inhibit or stop the process.

Red wines regularly go through MLF. For white wines, it is the winemakers choice.

Outcomes for the wine include lower acidity, higher pH, softer texture, better microbial stability (prevents the wine from spontaneously going through MLF at the wrong time), slight loss of fruit flavors, increase in buttery notes, increase on volatile acidity.

Question 29

Reverse osmosis

Answer 29

Post-fermentation must adjustment. The most common way to removal of alcohol. It works by filtering out alcohol and water from the wine, distilling that solution, and adding the water back into the wine. The equipment is costly.

Question 30

Spinning cone

Answer 30

Post-fermentation must adjustment to remove alcohol. Works by first extracting volatile aroma compounds from the wine. Then removing the desired amount of alcohol. Then blending the aroma compounds back into the wine. The technology is only viable for large volumes of wine.