PLP 150C1 1st Edition Lecture 8Outline of Last Lecture I. CharacteristicsII. King of yeastsIII. Sex lifeIV. Other important yeastsOutline of Current Lecture I. FermentationA. What is it?B. HistoryC. Aerobic vs. anaerobicII. Saccharomyces cerevisiaeIII. Fruit winesCurrent LectureYeasts in fermentation• They’re ubiquitous in nature & vary with many different strains• They vary on the kinds of sugars they ferment.• They vary in the temperature that they can tolerate.• Vary in the amount of acid they can tolerate.• Vary in the amount of alcohol they can tolerate.What is fermentation? The microbial conversion of carbs to alcohol or acids• Alcohol fermentation - sugar to ethanol & CO2.• Lactic acid fermentation with glucose - sugar to lactic acid (no CO2)• Lactic acid fermentation with lactose - lactose to lactate (no CO2)• Heterolactic acid fermentation - sugar to lactate, ethanol & CO2.◦ Those last 3 types are mainly bacterial processes but some yeasts can ferment these ways.Why ferment?• For recreation - probably the first use. Likely came about from natural yeast blooms in containers of fruit juices resulting in a bubbly beverage with a kick.• For preservation - likely a secondary consideration once people realized their fermented drinkdidn’t go bad, unlike fresh juice did.• For flavor - came around after many experiments, selections of strains, & control of the fermentation. History• First evidence of winemaking, 8000 years ago in Asia.• First evidence of mead, 7000 years ago in China.• First evidence of milk fermentation, 3000 years ago in Babylon.• First evidence of bread leavening, 1500 years ago in Egypt.Part 1:• Oxygen is present, so it’s called aerobic. This is the initial rapid process where the yeast is doubling cell counts every 4 hours. Important to build up yeast numbers to fill the fermentation environment. This is respiration.Part 2:• Oxygen isn’t present, so it’s called anaerobic. Slower activity & the yeast focuses on turning sugar into alcohol and CO1, rather than making a bunch of cells. This is fermentation.Many yeasts will ferment to ethanol, but Saccharomyces cerevisiae is the king.• But yeasts aren’t the only organisms that can do it.◦ Zymomonas mobilis is a bacterium that surpasses yeast in some aspects of fermentation. Degrades sugars to make ethanol and CO2, but more restricted ability to use a diversity of sugars. Can only use glucose, fructose and sucrose. Can ferment sugars to make wines and beers.• Biggest advantage of Zymomonas mobilis is making biofuels:• 1. Higher sugar uptake & ethanol yield• 2. Lower biomass production (less cell mass at the end, higher efficiency)• 3. Higher ethanol tolerance• 4. Doesn’t need controlled addition of oxygen during the fermentation• 5. Amenability to greater genetic manipulations.Fruit wines• Also called country wine.• Bananas are really popular in this kind of wine.• Most fruits & berries have potential to make win, but few have the correct balance of sugar, acids, and tannins.◦ Sugars - enough to get the yeast started, and enough to make sufficient alcohol for preservation◦ Acids - enough to prevent too much bacterial growth, but not too much to prevent yeast growth. Enough to contribute to flavor.◦ Tannins - These are antimicrobial at high concentration and aid in preservation. Contribute to flavor.• Most country wines are adjusted in many ways◦ Usually they add sugar.◦ Is usually lacks natural yeast nutrients that are necessary, so they add nitrogen, phosphorus and potassium.• Fruit wines don’t improve with bottle age, meant to be drank within a year of bottling.• Apple & Pear wines:• Perry or pear cider - made from pear juice, high amounts of sugar.• Apple cider - apples & high concentration of tannins. Generally doesn’t contain a lot of sugar.More preserved than