Factors Affecting Grape Microflora Moisture/Humidity Insect Vectors and Damage Temperature Vineyard Management Practices Variety of Grape Geography
Environmental Conditions that Affect the Microflora of Must pH - Low Nutrients - high sugar, variable nitrogen Temperature - fermentation creates heat Oxygen - fermentation is low oxygen Inhibitors - pesticides, sulfur, alcohol, acetic acid, etc. Winery Practices - additions, sanitation, stylistic considerations
Fungi found on Grapes Botrytis cinerea – bunch rot Plasmopara viticola – downy mildew Erysiphe necator – powdery mildew Penicillium – green mold Aspergillus – black mold Alternaria – black smut Cladosporium – post-harvest Rhizopus – soft rot
Bacteria in the - VineyardMustLactobacillus Lactococcus Pediococcus Enterococcus Weissella Weissella Gluconobacter GluconobacterAcetobacter PediococcusGluconacetobacter OenococcusLeuconostoc Oenococcus
Yeast in the – VineyardHarvested Grapes ZygosaccharomycesHanseniaspora HanseniasporaMetschnikowia IssatchenkiaCandida Kluyveromyces Metschnikowia Pichia Candida Rhodotorula Sporobolomyces Sporidiobolus
Yeast Found in Must Hanseniaspora uvarum, guilliermondii, opuntiae Metschnikowia pulcherrima Candida zemplinina, glabrata, diversa Pichia anomala, fermentans, guilliermondii Clavispora lusitaniae Zygosaccharomyces bailii Kluveromyces thermotolerans Kazachstania species Issatchenkia occidentalis, orientalis, terricola Saccharomyces cerevisiae
Saccharomyces in the Vineyard Saccharomyces occurs in only about 1 sound berry in 1000 tested In damaged berries that increases to about 1 in 4 berries tested The number of Saccharomyces cells on damaged berries is about 10 4 to 10 5 cfu/ml The total microbial counts in damaged berries is 10 6 to 10 7 cfu/ml
Typical Saccharomyces Growth Curve vs Typical Wine Fermentation Curve
Saccharomyces and Non-Saccharomyces Growth Curves vs Typical Wine Fermentation Curve
How Certain Groups are Selected Natural selection: Low pH High sugar concentration – high osmolarity Other nutrients High phenolic content Low oxygen Alcohol concentration
How Certain Groups are Selected Artificial Selection: Temperature Potassium metabisulfite pH - Tartaric acid Lysozyme Nutrients
What Are Some “Best Practices”? Harvest brix less than 27 o brix Harvest acid content – pH 3.2 to 3.6, TA 0.6 to 0.8 SO 2 added at the crusher Temperatures less than 30 o C Pump overs to manage temperature oxygen levels Addition of nutrients only as needed
Why Do Best Practices Work? What do they control?
Acid Adjustment High acid favors growth of yeasts early in fermentation Most microbes, especially bacteria, are not acid tolerant pH often increases during fermentation which favors the ML fermentation pH greater than 3.6 encourages spoilage lactics Brettanomyces is more tolerant to low pH
Addition of SO 2 Inhibits the growth of spoilage bacteria Inhibits growth of wild yeasts including Brettanomyces Destroys thiamin Inhibits oxidation
Inoculation Directly adds the desirable organism in high numbers
Engineering Practices Adjusting temperature – Cold soaks – Tank temperature, jacketed – Pump overs Adjusting oxygen – Cap Management – Pump overs – Rack and return – Punch down – Stirring or aeration – Micro-ox
Temperature Cold soaks (15-20 o C) encourage growth of non-Saccharomyces yeast early in fermentation Cool temperatures during fermentation inhibit growth of spoilage bacteria and some yeasts Warm temperatures can favor ML bacteria Cool storage temperatures discourage spoilage organisms during storage
Low Oxygen Strict aerobic organisms cannot compete under low oxygen conditions Filamentous fungi Acetic acid bacteria Anaerobic and facultative anaerobes grow under low oxygen Saccharomyces ML bacteria
Risks and Rewards Long hang times of fruit allow for development of desirable flavor and color and adds complexity Over doing it results in higher sugars that can produce too much alcohol that can arrest fermentation, leave residual sugars, and leave nutrients for spoilage organisms Acidity may also suffer and be too low allowing spoilage organism to flourish
Risks and Rewards Cold soaks can allow growth of wild yeasts that produce desired esters and other flavor compounds that add complexity Typically yeasts like Hanseniaspora, Pichia, and Candida occur Wild yeasts can also produce acetic acid and ethyl acetate in large amounts and this can be particularly risky with damaged fruit
Risks and Rewards Low oxygen prevents the growth of strict aerobic organisms like acetic acid bacteria and filamentous fungi Too much oxygen allows a bloom of aerobic organisms that often occur as a film on the surface of the wine Micro-ox done incorrectly in the presence of microbes, for example wood, results in the bloom of atypical microbes in wine
Case Study 1 A winemaker approached Dr. Bisson with a wine that had a mousey taste and low bacteria numbers by microscopic observation. No bacteria were found by plating or QPCR. The wine was filtered and filters plated on both bacterial (MLAB) and yeast (YM and WL) media.
What Is Causing the Contamination? There are many sources of bacterial contamination including: air, dust or soil, grapes, wood, water, and corks. The wines were typical except that the SO 2 level was low to none. The wines showed contamination with many species of bacteria. All of these wines were treated by micro-oxidation in the presence of wood.
What Is Causing the Bacillus Contamination? In bottling lines, Bacillus spores can survive heat treatments that have replaced chemical sanitation measures. Bacillus is a strict aerobe but is typically acid sensitive Ethanol is effective at inducing sporulation in Bacillus
Case Study #2 Wine was returned from the distributor due to high turbidity. Wine had no aroma or flavor defect, only high turbidity in some bottles. Bacteria were visible under the microscope but did not grow on plates and QPCR came back negative.
What was in the wine? Initial plating indicated Bacillus but the Bacillus didn’t look like what we saw under the microscope It might be Bacillus spores Looking further we also found moderately high levels of Staphylococcus pasteuri
The wine The wine was sweetened with added juice. I don’t know if the juice was filtered. Synthetic corks were used. The pH of the wine was high. The bottling line was cleaned with only hot water, bleach was no longer being used.
Best Practices Developed over time because they work How and why they work has not always been understood Significant deviation from the best practices rarely goes well