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The Science Behind Food Preservation:

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.

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The Science Behind Food Preservation:

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  1. The Science Behind Food Preservation: Dr. Renee Boyer Extension Specialist May 21, 2009

  2. Why Preserve Foods ? • Prevent Spoilage of Foods & Extend Shelf Life • Types of Spoilage: • Microbiological • Molds, yeast, bacteria • Chemical • Enzymatic changes • Physical • Bruising, water loss

  3. 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

  4. What Bacteria Need to Grow • Food • Acidity • Temperature • Time • Oxygen • Moisture FIGHT BAC!

  5. What Bacteria Need to Grow • Food • Acidity • pH = Amount of acidity • Low acid food = pH > 4.6 • Temperature • Time • Oxygen • Moisture

  6. Bacteria Inhibited by pH Most Inhibited Least Inhibited

  7. 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

  8. What Bacteria Need to Grow • Food • Acidity • Temperature • Danger zone = 40°F to 140°F (41°F - 135°F) • Time • Oxygen • Moisture

  9. What Bacteria Need to Grow • Food • Acidity • Temperature • Time • Oxygen • Moisture aw target = 0.85

  10. Food Preservation Goal: Control microbial growth / destroy microorganisms by: • High temperature (Heat) • Low temperature (Cold) • No oxygen • Low pH • Low Aw (water activity)

  11. Methods of Home Food Preservation: • Heat Processing/Canning • Boiling Water Bath • Pressure Canning • Freezing • Drying

  12. Canning = Preservation by Heat • Destroys microorganisms • Inactivates enzymes • Seals container during the process to prevent recontamination

  13. Question #1: Of the growth factors that we discussed, which is the most important to know before proceeding to canning?

  14. Question #2: What is the target organism associated with this?

  15. 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

  16. 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

  17. Question #3: Name one high acid and one low acid food

  18. High Acid Foods (pH < 4.5) Lemons Grapefruit Pineapple Apricots Cherries Figs Plums Raspberries • Apples • Oranges • Peaches • Strawberries • Pears • Sauerkraut, pickles • Blueberries • Rhubarb

  19. 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

  20. Tomatoes: • Usually considered an acid food • Some now known to have a pH slightly above 4.6 • Boiling water bath …MUST be acidified

  21. 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

  22. 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

  23. Time/Temperature Dependency • Food • Acid, salt, sugar, starch, fat • Size of Pieces • Consistency • Convection heating in liquids • Conduction heating in solids

  24. 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!!!

  25. 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

  26. 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

  27. 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

  28. 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

  29. Question #4: True or False: Altitude affects the canning process

  30. 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

  31. 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

  32. 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

  33. 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

  34. Appropriate Jars/Lids

  35. 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

  36. 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

  37. 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

  38. 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)

  39. 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

  40. 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

  41. 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

  42. 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

  43. 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

  44. Importance of temperature: • Frozen foods should be stored below 0°F to prevent deterioration of the product and improve quality Example:

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