Publications by Dr. Murli
Active Dry Yeast - 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.
Antimicrobial Agents - Food is essential for survival. Since the beginning, people have been interested in preserving food for later consumption. Overtime, many methods of food preservation have been tried. These include heating, freezing, drying, fermenting, and adding chemical preservatives. In recent years, the use of chemical preservatives has increased.
Apple Wine - Making fruit wines can be economically rewarding. A certain segment of the population enjoys these wines. A winemaker can produce high quality fruit wines as a specialty product and benefit from this existing niche in the marketplace.
Botrytis cinerea in Winemaking - 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.
Cold Stabilization by Contact Process - 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.
Copper Sulfate Trial - Hydrogen sulfide and other “sulfide-like” off aromas are commonly observed problems during fermentation. Sometimes these off odors are not very conspicuous and tend to mask the fresh and fruity aromas that one expects to find at the end of a sound fermentation.
Dangers of Oxidation in Table Wines - Missouri vintners produce some of the finest white table wines from French hybrid cultivars. Vignoles, Seyval, Vidal, and Cayuga White are the leading grape varieties used in premium white wine production. In 1992, Missouri wines received 240 awards in 17 wine competitions.
Determining Residual Sugar Using a Hydrometer - Many winemakers use a brix hydrometer having a scale of +5.0 to -5.0 to estimate the residual sugar content and evaluate the completion of fermentation. Although this is not an accurate method to determine residual sugar content in a wine, it does serve as an indicator of the progress of the fermentation.
Ethyl Carbamate Content in Wines - Ethyl carbamate is known for its carcinogenic effect on some laboratory animals; it has not been conclusively proven to be a carcinogen for human beings. Because of the suspicion that ethyl carbamate may pose a health risk, a considerable amount of research has been done.
Harvest Preparation - The harvest season is just around the corner. This is the busiest and the most critical period of the year. Organizing the crush and careful planning of this work is essential for a successful and trouble-free vintage. We will consider several topics to help you with the upcoming vintage.
Importance of Cleaning and Sanitation in the Winery - 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 sanitation.
Lactic Acid Bacteria and Wine Spoilage - Lactic acid bacteria (LAB) are responsible for many fermented foods such as sauerkraut, pickles and yogurt. They have also been isolated from wines at various states of vinification. In wines they are responsible for malolactic fermentation (MLF) which can be beneficial in some cases and undesirable in others.
Methods for Tartrate Stabilization of Wine - In the last issue (Jan/Feb, 1994) of Vineyard and Vintage View, the formation and precipitation of potassium bitartrate (KHT) was explained. In this issue, various methods of stabilizing wine, with respect to KHT, will be discussed.
Nitrogen Metabolism During Fermentation - Nitrogenous compounds play an important role in winemaking. They serve as nutrients for the growth and metabolic activity of the yeast during fermentation; and as proteins, they also influence wine stability, particularly in white wine.
Oak Aging of Red Wine - Maturation and aging can be considered as a group of reactions and series of changes that occur in wine during storage and lead to wine improvement. Boulton et al (1996) suggested that wine aging should not be viewed as a single procedure and a single event but rather a family of changes. They further suggested a distinction between the term maturation and aging.
Oak Wood Composition - Significant variation occurs in the composition of oak heartwood. There are many factors that contribute to this variation. These include: differences within a tree, age of the tree, rate of growth, soil and climate of the region, and more importantly, the genetic differences between various species.
pH and Protein Instability - Wine proteins are derived primarily from grapes and autolyzed yeast. They consist of several (protein) fractions which appear to be the subunits of denatured grape enzymes. Their molecular weight varies from 20,000 to 40,000 Daltons. The polypeptides with molecular weights of less than 10,000 are mostly derived from yeast autolysis. The isoelectric point (PI) of wine protein fractions have been reported to be in the range of 2.5 - 8.7.
Port Production - What does the word port mean? Usually people will think of a glass of sweet red wine. Most will know that it has been fortified. Very simply, that is exactly what port is; usually a red wine that tastes sweet, that has had brandy added to it. However, port is much more than this simplistic definition. It is my desire to instill enthusiasm for the drink and educate as to its production.
Post Fermentation Handling of Wines - Fermentation transforms the must into a young wine. Proper handling of young wines is very critical because mistakes made at this early stage can irreversibly damage the wine quality.
Preparing Standard Sodium Hydroxide Solution - In a wine laboratory, analyzing wine for TA, VA and S02 involves the use of a sodium hydroxide (NaOH) reagent. Winemakers usually buy sodium hydroxide solution of a known concentration (usually 0.1 Normal).
Problem Fermentation and Yeast Hulls - Premature cessation of an alcoholic fermentation, commonly known as a stuck fermentation, is a serious winemaking problem. Restarting a stuck fermentation is often difficult and time consuming, but more importantly, it creates a favorable condition for the growth and activity of spoilage microorganisms.
Protein Instability and Bentonite Fining - Turbidity or cloudiness in wine is one of the important problems known to occur in commercial table wines. Often the cloudiness in wine results from microbial activity. However, sometimes it is caused by proteins which are heat sensitive and unstable.
Racking - 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.
Racking 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.
Red Wine Production - The basic procedure of red wine production is outlined in the diagram. An important point in making red wine is that the fermenting must consists of juice skins and seeds. As a result, the composition of red wine is determines by the constituents extracted from skins and seeds in addition to those present in the juice.
Some Issues in Malolactic Fermentation - Reduction and Flavor Modification -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.
Sorbic Acid - A. W. Van Hoffman was the first to isolate sorbic acid from the berries of the mountain ash tree in the year 1859. The antimicrobial (preservative) properties of sorbic acid were recognized in the 1940's. In the late 1940's and 1950's it became commercially available.
Sources of Winemaking Information - All types of information on enology.
Sugar Addition Table - Many winemakers sweeten their wines by adding cane sugar which is usually done just prior to bottling. The extent of sweetening depends on the style of wine. The amount of sugar in wine is often expressed in terms of percent and calculated accordingly.
Titratable Acidity - 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).
Treatment for Removal of H2S - Copper sulfate trial. The first step in copper treatment is to experimentally determine the amount of copper needed for the wine treatment. This can be achieved by following the procedure given below.
Use of Inert Gases - Nitrogen and carbon dioxide are the most commonly used inert gases in the wine industry today. In some cases a mixture of these two gases in varying proportions is also used. The use of a particular gas depends on the type of wine and intended purpose.
Vinification of Botrytised Mus - In the previous issue of this publication, changes in fruit composition caused by Botrytis cinerea were discussed. These changes pose special vinification problems to a winemaker. In this issue these problems and how they can be handled will be discussed.
White Wine Production - A significant number of wineries in Missouri and other states are engaged in small-scale wine production. Some of the wineries are recent commercial ventures while many others have chosen to stay small due to the limitations of time and other resources. Regardless of the scale of production, the wineries must make high quality wines consistently in order to succeed in the business.
Wine Aeration and Its Adverse Effects - Prolonged contact with air is detrimental to wine quality. Certain wines, such as sherry and madeira, are exposed to air during the course of their production. On the other hand, premium table wines are produced with minimum or limited air exposure.
Wine Aging- 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.
Wine Corks- 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.
Wines From Cherries and Soft Fruits - Cherries grow best in a moderately cool climate. They are consumed fresh as well as processed for juice and other products such as wine. Sweet cherries are mostly grown in Oregon, Washington, and California because of the semi-arid climate. Lack of rain at harvest prevents cracking and rotting of the fruit.
Wine Yeast- It is often said that a "wine is made in the vineyard" or "you can't make a silk purse out of a sow's ear." These comments emphasize the point that good quality fruit is needed for good quality wine. Although the importance of quality grapes in making superior wine cannot be denied, it is equally important to realize that it is one of the critical components but not the only component necessary to make good wine. There are many other factors that are vital to wine quality, otherwise, how can one explain poor quality wine from high quality grapes?
Wooden Cooperage - Wooden barrels have been used in winemaking since the pre-Christian era. In early days, barrels were used for fermentation, storage, and transportation of wine. The winemakers realized that storage of wine in barrels improved wine quality.
Yeast Autolysis- The term autolysis literally means 'self-destruction'. It represents self-degradation of the cellular constituents of a cell by its own enzymes following the death of the cell.
Yeast Autolysis - The term autolysis literally means 'self-destruction'. It represents self-degradation of the cellular constituents of a cell by its own enzymes following the death of the cell. In the process of autolysis, the medium (wine) is enriched by the compounds released as a result of the degradation of intracellular constituents. These yeast constituents have an important influence on the sensory properties and biological stability of wine.