Grapes contain significant amounts of organic acids. The major organic acids in the must are tartaric, malic, and citric. Of these three acids, tartaric and malic acids account for over 90% of the total acid constituents of the juice (Amerine and Joslyn 1950). During ripening, the tartrate and malate content of the fruit decrease. This is accompanied by a steady increase in pH. Due to variation in buffer capacity, there is no direct relationship between titratable acidity and pH. In general, however, higher acid levels in fruit are often associated with lower pH values and vice versa. Thus the acids of the fruit have a significant bearing on pH. They also play a significant role in taste, color, and microbial stability of the juice.
Wine aging refers to a group of reactions that tend to improve the taste and flavor of a wine over time. The term wine 'maturation' refers to changes in wine after fermentation and before bottling. During this period, the wine is subjected to various treatments, such as malolactic fermentation, clarification, stabilization, and bulk storage.
Although there is some historical evidence suggesting that cork was used as a stopper about 2,000 years ago, its use became more prevalent with the introduction of glass bottles in the 17th century. In recent years, other alternatives such as capsules and plastic stoppers have been introduced as closures for wine bottles. However, cork still remains the principal closure of choice for premium wines.
When a fermentation ceases, the suspended particles settle rapidly and form a sediment. The sediment, referred to as lees, usually consists of macerated grape tissue, dead yeast cells and yeast autolysis products. The young wine is separated from the lees by transferring the wine to another container, leaving the lees behind. This process is called racking.
Grape juice/must can be fermented by the yeasts present on grapes and in the winery. This kind of fermentation is often called natural or spontaneous fermentation. Some winemakers rely on spontaneous (uninoculated) fermentation to gain flavor complexity and, consequently, higher wine quality. In some cases high quality wines have been produced from uninoculated fermentations; however, the practice is not without risk.
Botrytis cinerea is a mold responsible for fruit rot in many fruit plants. Grapes are susceptible to this fungus. Generally it causes bunch rot commonly known as botrytis rot or grey rot. It also creates conditions favorable for the growth of other spoilage organisms. Botrytis and a mix of other microorganisms including yeast, mold, and bacteria are involved in miscellaneous fruit rots.
Grape juice and/or wine can be considered as a supersaturated solution of KHT. Under certain conditions such as low temperature storage, the dissolved KHT becomes insoluble and small crystals settle to the bottom in the form of a sediment. In a supersaturated solution (e.g., wine) the crystallization process occurs in two stages. In the first stage, also referred to as nuclei or seed crystals are formed. It is important to note that for nucleation to occur in a supersaturated solution the concentration of KHT must reach a critical level.
Cleaning and sanitation is crucial to producing quality wine. Over the past couple of years several new wineries have been started in the state. It is important that the wineries have a good understanding of cellar hygiene. Beginning in this publication we will be offering information on this subject in a series of articles. The first article deals with the significance of cleaning and
Lactic acid bacteria (LAB) play an important role in winemaking. They are involved in malolactic fermentation (MLF), which is also called secondary fermentation. Malolactic fermentation causes acid reduction, flavor modification and also contributes to microbiological stability.