Introduction

The winemaking community worldwide continues to be a study of philosophical contrasts. On the one hand, there are those winemakers and wineries that emphasize the scientific segment of winemaking through adoption of new research findings and technologies. On the other hand, others prefer to embrace Old World traditions and thereby accentuate the artistic aspects associated with wine production. In writing this book, the objective was not to debate the relative merits and deficiencies of either...

Identification of Wine Microorganisms

Biologists use a system of identification based on the degree of physical and physiological similarity between organisms known as taxonomy. Early attempts at classification involved comparison of observable phenotypic features such as cell shape (morphology), as well as use of a variety of often crudely prepared sugar and nitrogen substrates. From these evolved extensive diagnostic schemes for identification, which still initially rely on cell and colony morphology. Today, other phenotypic...

Taxonomy

To distinguish yeasts that can produce ascospores from those that do not, mycologists use a dual taxonomy for classification. Unfortunately, the nomenclature for anamorph teleomorph combinations is frequently different. Examples of sexual asexual or teleomorph anamorph yeasts include Dekkera Brettanomyces, Metschnikowia pulcherrima Candida pulcher-rima, Hanseniaspora uvarum Kloeckera apiculata, and Torulaspora delbrueckii Candida colliculosa. Some yeasts only exist in the anamorphic form...

Carbon and Nitrogen

Microorganisms require sources of utilizable carbon and nitrogen for growth and metabolism. By changing the medium composition through selective exclusion or inclusion of ingredients, specific microorganisms or groups of microorganisms can be isolated from an otherwise diverse population. This is true even when the microorganism(s) of interest are present in relatively low populations. An example would be the use of lysine agar in which the amino acid lysine represents the sole utilizable...

Timing of Inoculation

When MLF starter cultures are used in the winery, the winemaker will be faced with the decision as to the timing of bacterial inoculation. Although cultures can be inoculated simultaneously with yeast or early in the alcoholic fermentation, some winemakers inoculate after completion of the alcoholic fermentation (Webb and Ingraham, 1960 Kunkee, 1967b 1974 Henick-Kling, 1993 Pompilio, 1993). In the survey of Fugelsang and Zoecklein (1993), 41 of red wine producers added starters during the...

Film Yeasts

The visual manifestation of oxidative yeast activity is the formation of a film, sometimes referred to as mycoderma. The film results from repeated budding of mother and daughter cells that, rather than separating, remain attached, forming chains that branch and rebranch to eventually cover the surface of the wine (Section 1.2.2.4). Initially, the yeasts can appear as floating flowers. If allowed to continue, growth may rapidly develop into a thick pellicle, which appears mold-like. Baldwin...

Asexual Reproduction

Psudomycelia Microscopy

Budding represents the most frequently encountered form of reproduction and, in the case of wet mounts from juice or fermenting wine, the only form that will be seen. Budding of the mother cell initially yields a bud and, eventually, a daughter cell after separation. Under optimal conditions, a single mother cell may bud many times during the cultivation period. However, under the restrictive conditions of fermentation, a single yeast will bud only three to four times. Here, the availability of...

Fermentation Problems 851 Sluggish Stuck Fermentations

A vinification problem of tremendous economic importance encountered by winemakers is slow alcoholic fermentation rates, especially in the case of fermentation of high-sugar musts (Alexandre and Charpentier, 1998 Bisson, 1999 Bisson and Butzke, 2000). Premature cessation of yeast growth and fermentation results in a wine with unfermented sugars and an ethanol concentration lower than expected (Fleet and Heard, 1993). The problem may manifest itself as sluggish activity during middle and later...

Spoilage Microorganisms 1121 Acetobacter

Control of Acetobacter in wines should be initially accomplished by limiting populations entering the winery on fruit and by implementing and maintaining an adequate sanitation program Chapter 9 . Because mold- damaged fruit will have higher populations of acetic acid bacteria than sound fruit Section 6.5.1 , use of the former can lead to increased Aceto-bacter infections in wines during post-fermentation storage. Therefore, the risk of pass-through infections can be reduced by maintaining...

Sulfur Dioxide

Allowable Sewer

Sulfur dioxide is widely recognized in both the wine and food industries for its antioxidative and antimicrobial properties. The current legal limit for SO2 in wines in the United States is 350 mg L, a concentration well above levels normally used by winemakers. Nevertheless, wines that contain greater than 10 mg L must disclose this information on the label. Because SO2 is a metabolite of yeasts during fermentation Section 1.5.2 , wines will usually contain some sulfite even though additions...