Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Overview of Problem Fermentations Linda F. Bisson Department of Viticulture and Enology Issues in Fermentation Management, 2011 Problem Fermentations Slow (sluggish) fermentation Stuck (incomplete, arrested) fermentation Off-character production – Hydrogen sulfide – Sulfur volatiles – Acetic acid – Undesired Esters Stuck and Sluggish Fermentations Stuck and Sluggish Fermentations Characterized by failure of yeast to consume sugar Multiple causes Difficult to treat Leads to reduced wine quality Fermentation Profile 5 1 Brix 2 3 4 Time 1: lag time; 2: max fermentation rate; 3: transition point; 4: post-transition fermentation rate; 5: overall time to dryness Fermentation Profile Lag time – Duration? Maximum fermentation rate – Rate value? – Duration? Transition point – At what Brix level? – How sharp? Post-transition fermentation rate – Value relative to max fermentation rate? – Length of time? – Brix/ethanol/nitrogen level at which it occurs? Overall time to dryness Fermentation Capacity Is a Function of: Yeast Biomass Concentration Fermentative Ability of Individual Cells Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient Limitation Nitrogen: most often limiting Phosphate can also be limiting Depending upon circumstances, micronutrient limitation may also be a problem – – – – Pitching yeast Deficiency in vineyard Microbial blooms prior to fermentation Loss during rehydration Causes of Stuck/Sluggish Fermentations Nutrient limitation Ionic imbalance Ionic Imbalance Ratio of K+:H+ Must be at least 25:1 Needs to be adjusted early in fermentation Probably important in building an ethanol tolerant membrane Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient imbalance Substrate inhibition Substrate Inhibition Transporters with a high substrate affinity can get “jammed” at high substrate concentrations F G G FG F Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient imbalance Substrate inhibition Ethanol toxicity Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient imbalance Substrate inhibition Ethanol toxicity Presence of toxic substances Presence of Toxic Substances Toxins may arise from the metabolic activity of other microbes Toxins may arise from metabolic activity of Saccharomyces Toxins may have arisen in vineyard, but are not inhibitory until ethanol has accumulated The Most Common Toxins Acetic acid Higher organic acids (C2 – C4) Medium chain fatty acids/fatty acid esters Acetaldehyde Fungicide/Pesticide residues Higher alcohols Higher aldehydes Killer factors Sulfur dioxide Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient imbalance Substrate inhibition Ethanol toxicity Presence of toxic substances Poor adaptation of strain Poor Adaptation of Strain Strain may not display ethanol tolerance Strain may have high nitrogen/vitamin requirements Strain may be a poor fermentor, but capable of dominating the fermentation Temperature effects Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient imbalance Substrate inhibition Ethanol toxicity Presence of toxic substances Poor adaptation of strain Low pH pH pH is reduced by metabolism of Saccharomyces Low pH musts (below pH 3.0) may drop to an inhibitory level (pH 2.7) Dependent upon K+ concentration Causes of Stuck/Sluggish Fermentations Nutrient limitation Nutrient imbalance Substrate inhibition Ethanol toxicity Presence of toxic substances Poor adaptation of strain Low pH Temperature shock Problem Fermentation Profiles Types of Problem Fermentations 30 Normal Long Lag 25 Becoming Sluggish Sluggish Throughout Brix 20 Abrupt Arrest 15 10 5 0 0 50 100 150 200 -5 Time (hours) 250 300 350 Types of Sluggish Fermentations Long Lag Types of Problem Fermentations 30 Normal Long Lag 25 Becoming Sluggish Sluggish Throughout Brix 20 Abrupt Arrest 15 10 5 0 0 50 100 150 200 -5 Time (hours) 250 300 350 Causes of Long Lag Poor health of starter culture Presence of inhibitors Poor grape quality – Mold infestation – Premature initiation of fermentation Poor Health of Starter Culture Active Dry Yeast: Natural Fermentation: Yeast numbers low Inhibitory microbes present Poor yeast strain present Past expiration date Not hydrated properly Not stored properly Presence of Inhibitors Sulfur dioxide concentration too high Sulfur dioxide added improperly Microbial activity resulting in inhibition Pesticide/fungicide residues on grapes at harvest Temperature of must/juice too high/low Poor Grape Quality Infected grapes: loss of micronutrients Infected grapes: high microbial loads Loss of free oxygen Types of Sluggish Fermentations Long Lag Slow Rate Over Entire Course of Fermentation Types of Problem Fermentations 30 Normal Long Lag 25 Becoming Sluggish Sluggish Throughout Brix 20 Abrupt Arrest 15 10 5 0 0 50 100 150 200 -5 Time (hours) 250 300 350 Causes of Slow Rate Over Entire Time Course Failure to reach maximum cell density Nutrient (growth factor) limitation Strain a poor choice for conditions Inhibitory fermentation conditions: temperature, pH, ionic imbalances Types of Sluggish Fermentations Long Lag Slow Rate Over Entire Course of Fermentation Rapid Rate Becoming Slow Types of Problem Fermentations 30 Normal Long Lag 25 Becoming Sluggish Sluggish Throughout Brix 20 Abrupt Arrest 15 10 5 0 0 50 100 150 200 -5 Time (hours) 250 300 350 Causes of a Decrease in Rate Poor ethanol tolerance Loss of viability Loss of fermentative capacity Nutrient (survival factor) limitation Poor strain Types of Sluggish Fermentations Long Lag Slow Rate Over Entire Course of Fermentation Rapid Rate Becoming Slow Abrupt Stop Types of Problem Fermentations 30 Normal Long Lag 25 Becoming Sluggish Sluggish Throughout Brix 20 Abrupt Arrest 15 10 5 0 0 50 100 150 200 -5 Time (hours) 250 300 350 Causes of an Abrupt Stop Temperature shock Rapid build up of inhibitors: acetic/organic acids pH decreases too much Strain very ethanol sensitive Most Common Causes of Stuck/Sluggish Fermentations Temperature extreme Ethanol intolerance Nutrient deficiency Deficient yeast strain Microbial incompatibility Presence of an inhibitory substance Poor fermentation management decisions Why are stuck fermentations difficult to treat? Cells adapt to adverse conditions by reducing fermentation capacity Biological adaptation difficult to reverse Diagnosis of cause of fermentation problem difficult Conditions that cause stuck fermentations are also conducive to cell death New inocula respond to cell death by arresting activities