Quiz - Options for Winemaking

Question 1

Wine is made up of an array of different compounds, some of which come directly from the grapes and others which have been formed during the fermentation process or added as part of other winemaking procedures.

Identify the seven main groups that these compounds can be roughly split into.

Answer 1

1. Water
2. Alcohol
3. Acids
4. Wine aromatics
5. Residual sugars
6. Glycerol
7. Phenolics

Question 2

The EU has a set of classifications for still wines. This means that wines are classified by the use of different labeling terms. Name the labeling terms in different languages to the English definition.

Answer 2

Dry – Trocken, Sec

Medium dry - Halbtrocken, Demi-sec

Medium sweet – Lieblich, Moelleux

Sweet – Süß, doux

Question 3

Name the main aromatic and non-aromatic compounds that can be found in wine.

Answer 3

Aromas from grapes - Methoxypyrazines and Rotundone

Aromas created by fermentation due to the presence of aroma precursors in grape must - Thiols and Terpenes

Aromas originating from fermentation and its by-products - Esters, Acetaldehyde and Diacetyl

Aromas from other sources - Vanillin and Eucalyptol

Question 4

What is the main aim of the interventions made during modern/conventional winemaking?

Answer 4

The aim is to produce stable wines which reliably show their fruit character and have no faults.

Question 5

How much SO2 can be added to organic wines in the EU and the USA?

Answer 5

In organic wine production in the EU, the addition of SO2 (Potassium metabisulfite) to wines to stabilize them is permitted in regulated amounts (between 100 and 400 mg/l depending on wine style).

In the USA, the addition of SO2 is forbidden in organic viticulture and the amount of naturally-occurring SO2 must be below 10 mg/l.

Question 6

Name an unwanted aroma compound as a result of oxidation

Answer 6

Acetaldehyde – occurs in wines due to the oxidation of ethanol

Question 7

What is the word for the headspace of air between the wine and the top of vessel?

Answer 7

ullage

Question 8

Which inert gases are often used to flush out oxygen, or fill the empty headspace of wine vessels?

Answer 8

• Carbon dioxide
• Nitrogen
• Argon

Question 9

Grape growers may choose to transport grapes to the winery in large hoppers/bins.
What is added before transport to avoid microbial spoilage and minimize oxygen contact?

Answer 9

SO2

Question 10

Briefly describe the options that are available to a winemaker when it comes to sorting the grapes for quality wines.

How might these options differ to those used on inexpensive wines?

Answer 10

The options for the winemaker are as follows:

• Prior to harvest, any diseased, damaged and unripe fruit can be removed by hand in the vineyard or at harvest time, if picked by hand.
• On arrival in the winery sorting the grapes on a table or conveyor table that vibrates can be carried out by hand.
• Optical sorting has a high cost but can be carried out either on a machine harvester or in the cellar. The criteria for the grapes are set by the winemaker and the machine scans the berries, rejecting any berries that do not fit the criteria.
• Sorting is generally only carried out on quality wines as it is expensive. If sorting is carried out on inexpensive wines it may be at harvest time and only if the grapes are handpicked.

Question 11

What type of press would be most appropriate for making high quality wines?

Answer 11

Pneumatic press

• Pneumatic presses can be programmed to exert different amounts of pressure
• The amount of time the skins spend in contact with the juice can be altered.
• Oxidation can be managed more efficiently by the use of inert gases before pressing.

Question 12

The process of enrichment usually takes place before or during fermentation, and the aim is to increase the alcoholic content of the final wine. List 5 forms of enrichment:

Answer 12

• Vacuum evaporation – water in the must evaporates in vacuum at temperatures of 20°C
• Cryoextraction – freezing the must or even final wine, and removing ice from it
• Reverse osmosis with cross flow filtration
• Chaptalisation (addition of dry sugar)
• Addition of RCGM (rectified concentrated grape must)

Question 13

Grapes (particularly those grown in hot climates) often dramatically drop in acidity when ripening. Different acids are frequently added during processing to raise the acidity levels. Which acids are typically added?

Answer 13

Malic acid - not as frequently used as it can be turned into lactic acid by malolactic conversion.

Tartaric acid - often used to mimic the acidity in grapes

Citric acid - not permitted to be used for the purposes of acidification in the EU

Lactic acid - usually tastes less harsh than the other acids

Question 14

Where does the need to deacidify arise and how is it done?

Answer 14

In contrast to hot climates, the grapes grown in cold climates often contain high levels of acidity. This often occurs when grapes have to be picked before they are fully ripe due to poor weather.

Wine makers can choose to deacidify by adding calcium carbonate (chalk) or potassium carbonate - both of these methods deacidify by forming tartrates in the wine.

A more modern version that requires considerable investment is deacidifying by ion exchange.

Question 15

What is the term for the cost-effective method of exposing wine to oxygen by bubbling oxygen through the wine?

Answer 15

Micro-oxygenation

Micro-oxygenation is generally carried out in stainless steel tanks for a number of months post alcoholic fermentation. Initially, micro-oxygenation was generally used on inexpensive and mid-priced wines; however, a growing number of wineries producing premium and super-premium wines are now using the technique.

Question 16

Wines are often matured in stable conditions to control the rate of oxidation. Briefly describe how a winemaker may moderate these conditions. Remember to include details on the optimal conditions for maturation and the adverse effect experienced if these conditions are altered.

Answer 16

• Temperature plays a key role in the rate of oxidation. The recommended temperature for white wine maturation is 8-12ºC (46-54ºF) and for red wines 12-16ºC (54-61ºF). These cooler temperatures ensure the rate of oxidation is slow, constant and stable which slows down the maturation rate.
• With warmer temperatures the rate of oxidation increases which leads to undesirable aromas and flavor profiles in the wine.
• If wines are matured in barrel, humidity is a key factor and should be kept above 70% to control the rate of evaporation. Increased evaporation rates affect the volume of wine in barrel.

Question 17

Briefly detail the basic production processes which are usually undertaken when making an oak barrel intended for wine maturation. Give details on why these production processes are completed and what effect they have on the wine.

Answer 17

• Depending on the origin of the oak, the process of making the staves is very different. For American oak, the wood is sawn which is a cheaper process as more staves can be produced from a log; for European oak, the staves are split.
• The staves need to be seasoned, preferably outside, to reduce humidity levels, reduce the bitter flavors and increase some desired aroma compounds (e.g. cloves) in the wood.
• The staves are then heated so they can be bent into shape which also impacts the tannin and aroma compounds in the oak. The temperature and length of ‘toasting’, as the heating process is referred to, will vary from light-, medium- or heavy-toasted.
• Aromas of spice, caramel, roasted nuts, char and smoke are imparted from the ‘toasting’ process. The level of toasting will impart more or less of these aromas to a wine.

Question 18

What is the term for the process when the yeast cells will very slowly die post-fermentation and start to break down?

Answer 18

autolysis

Wine is often matured on these dead yeast cells since they contribute flavors, body and texture to the wine.

Question 19

The term ‘blending’ is often used in winemaking specifically for which of the following processes?

Blending is putting grapes together from different …

Answer 19

• vessels
• treatments in the winery
• grape varieties
• grape growers
• vintages
• locations, vineyards, regions or countries

Question 20

Explain the seven main reasons for blending wines.

A winemaker may choose to blend for more than one of these reasons; give brief details on why each of the reasons may be required.

Answer 20

• Balance can be many things in a wine including acidity i.e. blending high acid grapes with lower acid grapes, blending high sugar grapes with lower sugar grapes, blending different grape varieties that add different aromas and characteristics to the overall wine i.e. Cabernet Sauvignon blended with Merlot.
• Consistency is key for certain wine styles i.e Sherry and non-vintage Champagne but also for inexpensive large volume still wines. The consumer wants a guarantee of quality and consistency of flavor when they buy these wine styles; vintage variation is not an option.
• Style can be tied in with consistency, certain wine styles have a perceived style which is expected each year, irrespective of vintage variation.
• Complexity can be increased by blending different varietals and different wines that may have been treated differently in the cellar, increasing the range of flavors in the finished wine.
• Minimizing faults is only when the fault is minimal to start with i.e. higher than accepted levels of volatile acidity (VA) blended with a wine with no perceived VA.
• Volume can be increased by blending with grapes, must or wine that has been bought in from another producer.
• Price can be maintained by blending more expensive varietals with less expensive varietals, Chardonnay has a higher market value and will get more money if sold as such even if it is blended with a lesser (inexpensive) grape variety like Semillon.

Question 21

Fining speeds up the process of the precipitation of suspended material in the wine with the use of a fining agent.

Briefly define the most common fining agents and their primary uses.

Answer 21

Removal of unstable proteins:
* Bentonite - Clay which absorbs unstable proteins/colloidal coloring matter. Doesn’t affect flavor and texture of wine much but leads to some colour loss in red wines. Produces large amounts of sediment.

Removal of phenolics that contribute undesirable color and bitterness
Egg white - Used in fresh or powdered form. Mainly used for high-quality red wines to gently remove harsh tannins and clarify wine.

Gelatin - Removes bitterness and astringency in red wine and browning in white wine pressings. Can strip flavor and character, and create protein haze forming later.

Casein - A milk-derived protein that removes browning from white wines and clarifies wines to some extent.

Isinglass - Clarifies white wines, giving them a bright appearance. Can form a protein haze and produce a fishy smell if overused.

Vegetable protein products - Derived from potato or legumes and suitable for vegan-friendly wines.

PVPP - An insoluble plastic in powder form that removes browning and astringency from oxidized white wine. It is rarely used on red wines, but can reduce astringency and brighten the color.

Removal of color and off-odors.
Charcoal - Removes brown colours and some off-odors. Over-fining can easily remove desirable aromas and flavors.

Question 22

Filtration is the most common way of clarifying wine. The wine is passed through a filter medium to eliminate the solids in the wine. Describe the most common types of filtration:

Answer 22

The following types of filtration exist:

Depth Filters

- Diatomaceous earth:
Uses pure, inert silica also known as Kieselguhr. Comes in a range of particle sizes, so can remove large or small yeast particles. Must be disposed of responsibly, which carries a cost.

- Sheet filters:
The wine is passed through layers of filtering material. Requires investment initially but the cost of upkeep is low.

Surface Filters

- Membrane filters:
They catch particles that will not go through the pore size of the filter, which are often smaller than 1 micron. For the same reason, wine must be pre-filtered first to avoid blockage. The initial investment is small, but the cartridges are expensive. Often done just pre-bottling.

- Cross-flow filters:
Wine passes through the filter while uniquely cleaning the surface of the filter as it works. Solid particles cannot pass through the filter. No parts or equipment need to be replaced, but the machinery is expensive.

Question 23

Tartrates are deposits of crystals, usually formed from potassium bitartrate and sometimes calcium tartrate. Although these crystals are harmless, they are often regarded as a fault.

Therefore, many wineries try and prevent them via which methods?

Answer 23

Cold stabilization: The wine is held at -4°C (25°F) for around eight days; this causes the tartrates to form before bottling so they can be filtered out. Colloids must be removed by fining before this process as they could prevent the crystals from forming at this stage. This process only removes the more common potassium bitartrate, not calcium tartrate.

Contact process: This is a quicker, continuous, more reliable, and cheaper method. Potassium bitrartrate is added to the wine and speeds up the start of the crystallization process. Wine is usually cooled to around 0°C (32°F) and after one or two hours the resulting crystals are filtered out.

Electrodialysis: This process uses a charged membrane to remove selected ions. It removes both potassium and calcium ions and, to a smaller extent, tartrate ions.

Ion exchange: This process does not remove tartrates but replaces potassium and calcium ions with hydrogen or sodium ions (as they will not drop out of solution).

Carboxymethylcellulose (CMC): This cellulose is extracted from wood and prevents tartrates from developing to a visible size. Often used on inexpensive white and rosé wines, but is not suitable for red wines. It is much cheaper than chilling.

Metatartaric acid: Adding this compound prevents the growth of potassium bitartrate and calcium tartrate crystals. However, the compound is unstable, and its positive effect is lost over time, especially when wine is stored at high temperatures.

Question 24

Describe the most common wine faults.

Answer 24

Re-fermentation in bottle:
Visible bubbles or spritz in wine, accompanied by cloudiness.

Tartrates:
Formation of colorless or white crystals in the bottom of bottle that can be mistaken for fragments of glass.

Cork taint:
Wine has a mouldy, wet cardboard smell, which also reduces the fruit character and finishes short on the palate.

Volatile acidity:
Wine has a pungent smell of nail varnish and/or vinegar.

Oxidation:
The wine is prematurely brown in color, with a loss of primary fruit and caramel aromas.

Light strike:
Wine can smell like dirty drains.

Brettanomyces:
Wine can have a range of off-aromas from animal, sticking plaster or farmyard smells.

Reduction:
Wine has sulfur-like odors similar to onion or rotten eggs.

Question 25

Briefly describe the optimum conditions for maturing premium German Riesling. Make sure you cover the following areas and describe why other options have not been chosen:

• Packaging/closures
• Effect of oxidation
• Storage and storage conditions

Answer 25

This wine will develop positively in bottle for many years, so the ingress of oxygen needs to be slow and controlled. Glass bottles will be the choice of packaging as they are impermeable.

The choice of closure will be assessed based on its oxygen transmission rate (OTR); different closures including natural/technical corks and screwcaps, have different rates. The most likely choice will be a high-quality cork allowing a slow ingress of oxygen over a period. This small amount of oxygen will have a positive impact on the aroma and flavor profile of the wine.

The recommended environment for ageing wine in bottle is a cool dark room with a constant temperature of between 10-15ºC/50-59ºF and humidity levels of approximately 70%. The wine bottles should be stored on their sides to protect the corks from drying out.

Question 26

Imagine you are shipping a high volume, inexpensive red wine from Australia to England. Briefly assess the pros and cons of bulk shipping versus shipping in bottle for this wine.

Answer 26

Pros of Bulk:
* More environmentally friendly as containers can carry more wine equivalent than if shipped in bottle, reducing the carbon footprint of the wine.
* Cheaper to ship in bulk due to less weight, as mentioned above.
* There’s less temperature fluctuation, which means there’s a lower chance of spoilage.
* The shelf life of the wine is extended as it’s calculated from point of bottling. This means the wine stays fresh for longer.
* The quality of the wine (checks for spoilage) can be checked at the point of origin and destination. Adjustments to the wine can also be made to the wine at the destination if required.

Cons of Bulk:
* There’s a loss of employment opportunities in the country of origin as bottling isn’t required.
* Only commercially viable for large producers.
* Only suited to certain wine styles.

Pros of Bottle:
* The marketing and branding of the bottle can be totally controlled at the origin.
* The quality can be controlled by the producer.

Cons of Bottle:
* Costs more as the weight is much higher for bottles.
* There is a greater impact on the environment due to inefficiency of shipping/quantity that can be transported.
* Wine can be damaged due to fluctuating temperatures in transit.
* Labels and packaging can be damaged.
* The shelf life of the wine will be decreased as it was bottled at source before shipping.
* Given that the wine is inexpensive, the associated relative costs of shipping in bottle are higher.