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Discover the science behind food preservation with Dr. Renee Boyer, where you'll learn about spoilage types, microbiological factors, and essential preservation methods. Explore the importance of acidity levels, target organisms, and high/low acid foods to ensure safe and effective preservation techniques. Unveil the secrets of canning, freezing, and drying foods to extend shelf life and maintain food quality. Learn the time/temperature dependencies and essential tips for successful food preservation.
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The Science Behind Food Preservation: Dr. Renee Boyer Extension Specialist May 21, 2009
Why Preserve Foods ? • Prevent Spoilage of Foods & Extend Shelf Life • Types of Spoilage: • Microbiological • Molds, yeast, bacteria • Chemical • Enzymatic changes • Physical • Bruising, water loss
Microbiological Food Spoilage: • Microorganisms can get onto a food product from anywhere in the environment… • People, animals, dirt, insects, other surfaces Spoilage microorganism: cause food to spoil NOT pathogenic!! Pathogens: make you sick
What Bacteria Need to Grow • Food • Acidity • Temperature • Time • Oxygen • Moisture FIGHT BAC!
What Bacteria Need to Grow • Food • Acidity • pH = Amount of acidity • Low acid food = pH > 4.6 • Temperature • Time • Oxygen • Moisture
Bacteria Inhibited by pH Most Inhibited Least Inhibited
What Bacteria Need to Grow • Food • Acidity • Temperature • Time • Oxygen • Moisture Aerobic: most spoilage organisms Facultatively anaerobic: 5% Oxygen pathogens Anaerobic: No Oxygen Clostridium botulinum
What Bacteria Need to Grow • Food • Acidity • Temperature • Danger zone = 40°F to 140°F (41°F - 135°F) • Time • Oxygen • Moisture
What Bacteria Need to Grow • Food • Acidity • Temperature • Time • Oxygen • Moisture aw target = 0.85
Food Preservation Goal: Control microbial growth / destroy microorganisms by: • High temperature (Heat) • Low temperature (Cold) • No oxygen • Low pH • Low Aw (water activity)
Methods of Home Food Preservation: • Heat Processing/Canning • Boiling Water Bath • Pressure Canning • Freezing • Drying
Canning = Preservation by Heat • Destroys microorganisms • Inactivates enzymes • Seals container during the process to prevent recontamination
Question #1: Of the growth factors that we discussed, which is the most important to know before proceeding to canning?
Question #2: What is the target organism associated with this?
Acidity: the most important factor! • Clostridium botulinum • Spore-former: spores ubiquitous in the environment • Can’t make you sick • Infant botulism • ONLY: Under anaerobic conditions (commonly created during preservation), spores germinated into vegetative cells • Vegetative cells produce toxin
Botulism: • Ingestion of toxin in foods • Neurotoxin • Causes paralysis and death if medical attention isn’t found quickly • Very rare in U.S. now • Primarily associated w/ improperly home canned
Question #3: Name one high acid and one low acid food
High Acid Foods (pH < 4.5) Lemons Grapefruit Pineapple Apricots Cherries Figs Plums Raspberries • Apples • Oranges • Peaches • Strawberries • Pears • Sauerkraut, pickles • Blueberries • Rhubarb
Low Acid Foods (pH > 4.5) • Meat, fish • Carrots • Green beans • Potatoes • Peas • Cabbage • Corn • Squash • Pumpkin • Okra • Turnips • Snap Beans • Sweet potatoes • Onions • Oysters • Ripe olives
Tomatoes: • Usually considered an acid food • Some now known to have a pH slightly above 4.6 • Boiling water bath …MUST be acidified
Canning Foods • Low acid foods: • pH >4.6 • Processing Pressure canner! • High acid foods: • pH <4.6 • Boiling water bath • Acidified foods: • pH is decreased to <4.6 by adding acid • Pickling, salsas, tomatoes! • Boiling water bath
Destruction of Spores in Low Acid foods: • Spores are very difficult to destroy at boiling temperatures • Boiling water bath: 212°F • 7 – 11 hours depending on the food • Pressure canning: 240 – 250°F (10-15 psi) • 20 – 100 minutes depending on the food
Time/Temperature Dependency • Food • Acid, salt, sugar, starch, fat • Size of Pieces • Consistency • Convection heating in liquids • Conduction heating in solids
Time/Temperature Dependency • Combination of both • Fullness of pack • Container size and material • Initial temperature of food • Microorganisms presen • WHEN CANNING ALWAYS USE A RECIPE FROM A REPUTABLE SOURCE!!!
What are reputable sources? • National Center for Home Food Preservation • http://www.uga.edu/nchfp/ • USDA Complete Guide to Home Canning • http://www.uga.edu/nchfp/publications/publications_usda.html • Ball Blue Book
Methods of canning NOT recommended: • Open-kettle canning • Processing in conventional ovens, microwaves, dishwashers • Do no prevent all spoilage risks • Steam canners • Do not heat as effectively • Canning at pressures greater than 15 • Use of glass caps or one piece zinc/porcelain-lined caps • Failure to seal properly
Boiling water bath canning: • Large covered cooking pot with a rack • Must be deep enough to cover 1 inch above jars • Processes foods at boiling temp. (212°F) • Acid / acidified foods • Heat destroys m/o that spoil acid foods
Pressure Canning: • Heavy pot, lid can be sealed: fitted w/ vent and pressure dial or weighted gauge • Processes foods at 240°F (10-11 pds pressure) • ONLY safe way to process low acid foods
Question #4: True or False: Altitude affects the canning process
The Effects of Altitude: • Water boils at lower temperatures as altitude increases. • Lower temps are less effective, so: • Boiling water bath: processing time increased • Pressure canning: pressure increased • Altitudes in WV vary greatly: Morgantown: 960 ft Beckley: 2421 ft
Weighted –vs- Dial gauge: Weighted gauges: Dial Gauges: 0-2000ft: 11 lbs pressure Over 2000ft: corrections must be made Ex: 2001ft-4000: 12 lbs 4001 – 6000: 13 lbs • 0-1000ft: 10 lbs pressure • Over 1000ft: must be operated at 15 lbs pressure
Ensuring Quality: • Use only high quality foods, free of bruises and blemishes • Can/preserve w/in 6-12 hours of harvest • Hot pack (especially acid foods) • Helps to remove air from the food • Keeps food from floating in jar • Increases the vacuum seal • Helps food maintain color during storage
Importance of headspace: • Jams/jellies: ¼ inch • Fruits / tomatoes: (boiling water bath): ½ inch • Low acid: 1-1 ¼ inch • Needed for expansion of the food • Higher the temperature, the greater the expansion • Forming vacuum in cooling jars
Important notes: Fruit • Some recipes call for ascorbic acid dip • Apples, pears, nectarines, apricots, peaches etc…. • Pure powdered form • Vitamin C tablets • Commercially prepared mixes • This dip prevents the fruit from browning while preparing jars
Important notes: Pickling • Pickled foods are acidified, therefore they can be heat processed in a boiling water bath • Prevents spoilage organisms and inactive enzymes • Fermentation • Dill pickles/saurkraut – 3 weeks • Refrigerated dill pickles – 1 weeks • Quick process – not fermented
Important notes: Pickling • Level of acidity should not be altered • Recipe MUST be followed • Use canning/pickling salt • Other salt has non-caking material added which can make brine cloudy
Important notes: Jams and Jellies • Ingredients • Fruit, pectin, acid, and sugar • Pectin • Form a gel when in the right combination of acid and sugar • All fruits contain some pectin • Fully ripened fruit has less pectin (when not adding pectin, ¼ fruit should be under-ripe)
Important notes: Jams and Jellies • Acidity • Too much – gel won’t set • Too little – gel with lose liquid • Low acid fruits must have lemon juice added • Commercial pectins contain acid to help w/ gelling • Reduced sugar • Must be made w/ low-methoxy pectin (requires addition of calcium to gel) • Typically need to be processed longer
Jams/Jellies and Mold • Low water activity + acidity typically prevents most spoilage • Except: MOLDS • Mycotoxins have been found in jellies/ jams which have surface mold growth • Known to cause cancer • PROCESS in boiling water bath • 5 minutes • Do not use paraffin or wax seals
Freezing: Easiest, most convenient quickest methods Freezing is the safest method, but may not produce the best quality Does not sterilize foods Retards the growth of m/o and slows down chemical changes that affect the quality of the foods
Control of Enzymatic Spoilage: • Enzymes are slowed down considerably, but not eliminated during freezing. • For best quality: • Vegetables: Blanched • Quick treatment in boiling water (2-3 min) inactivates enzymes prior to freezing • Fruits: Ascorbic acid is added • Vit. C, lemon juice, citric acid added to prevent browning before freezing
Changes during freezing: • Water in food freezes and expands • Ice crystals formed cause cell water to rupture rendering the product softer when defrosted. • Quicker freezing decrease amount of cell wall rupture • Rapid freezing: many small ice crystals form • Slow freezing: few large ice crystals • Most commercial products are frozen VERY rapidly in blast freezers
Importance of temperature: • Frozen foods should be stored below 0°F to prevent deterioration of the product and improve quality Example: