Chemistry Questions

Also called selected yeast or commercial yeast, this is a strain selected in a laboratory and grown in volumes suitable for scale.

-Adding dry sugar-Adding grape must-Adding grape concentrate or rectified concentrated grape must (RCGM)-Concentration through reverse osmosis, vacuum extraction, or chilling

Advantages-Reliable, fast fermentation to dryness-Low levels of volatile acidity and less risk to spoilage-Consistency-Large selection of strains available to choose from Disadvantages-Some believe it creates similarity of fruit expression (i.e., industrial wine)-Adds to costs of commercial product

In white winemaking, grapes are almost always pressed to extract juice from the grapes and to separate skins from the juice before fermentation. In red winemaking, the grapes are crushed before fermentation and pressed after the desired number of days on the skins (or at the end of fermentation).

The most popular type of press, also called "air bag presses," the press is made up of a cylindrical cage with a bladder that runs down the side or middle. Grapes are loaded in, the bladder inflates, and the grapes are pushed against grates on the side of the cage, separating juice or wine from skins. These presses can be programmed to exert different amounts of pressure and flushed with inert gas to protect from oxidation.

Crushing occurs at the beginning of the wine making process, where application of sufficient pressure breaks the skins of the grapes, releasing juice and making it available for fermentation.

The combination of grape juice, pulp, skins and seeds that come out of a crusher. For white wines, must may also refer to grape juice that is fermented. In general, "must" typically refers to the substance being fermented.

Common in cooler climates, winemakers may enrich must before or during fermentation to increase alcohol content of the final wine.

Similar to a basket press but mounted horizontally above a rectangular draining tray. It is less gentle than other presses and therefore less popular. It requires batch processing and is more labor intensive.

A greater proportion of free SO2 is in the molecular form at lower pH levels, meaning a greater amount of SO2 is required in musts and wines with higher pH to protect them from oxidation and microbes.

1. Harvesting / transporting at night when temperatures are cooler2. Additional of SO2 at harvest3. Reducing temperature by putting grapes in cold storage at reception4. Sanitizing harvesting equipment5. Transporting grapes in small crates to minimize crushing

Aroma compounds break down in the presence of oxygen, leading to a loss of fruitiness. Additionally, ethanol oxidizes to ethanal (or acetaldehyde), contributing nutty, apple aromas. White wines can become darker, and therefore need greater protection. Phenolic compounds in red wines are more anti-oxidative, and can absorb more oxygen before effects become perceptible.

Oxygen promotes healthy yeast populations, and in some cases, too little can lead to reductive off-flavors. For some white wines, exposing must to oxygen before fermentation can lead to greater oxidation stability and better aging potential. In red wines, oxygen promotes reaction between anthocyanins and tannins, for greater color stability.

-The ripeness and health of the fruit at arrival-The intended final wine quality and price-Whether sorting has been carried out in the vineyard-The physical state of the grapes

1. Avoid ullage in vessels by ensuring vessels are filled to the top, or topped up regularly2. Use inert gases such as nitrogen, carbon dioxide and argon to flush out oxygen from vessels, pipes and machinery (or to fill empty headspace)3. Add sulfur dioxide4. Use impermeable containers5. Keep temperatures cool and constant

1. Anti-oxidation; it reacts with oxygen very slowly, reducing the effects of oxidation.2. Anti-microbial; it inhibits the development of microbes such as yeast and bacteria.

1. Cap management techniques that spray or splash the must or wine2. Small wooden barrels for storage and aging3. Increase the number of rackings or lees stirring4. Allow ullage in the containers5. Pump oxygen through the wine (hyperoxidation, micro-oxygenation, etc.)

1. Removing before picking or at hand-harvesting2. Sorting by hand on a table or moving vibrating belt, before or after destemming3. Optical sorting

When SO2 is added to must or wine and dissolves, reacting with compounds in the liquid. It is ineffective against oxidation and microbes. The rest of the SO2 that does not react is called "free SO2." The majority of free SO2 exists in relatively inactive form, and a small proportion exists as molecular SO2 which is most effective against oxidation and microbes.

Solutions that are basic are also called ___________ solutions.