Lab 3: Food Preseveration: Canning, Freezing, Drying Flashcards
which people need to watch out for canned foods?
People who are on a sodium or carbohydrate restricted diet (hypertension or diabetes)
What are the main causes of deterioration in foods?
Microbial growth, enzyme action, and insect damage
During canning, what is ‘processing’?
Heating jars of food to temperatures high enough to destroy microorganisms and enzymes.
Processing drives air out of jars, and as the jar cools, an airtight vaccuum seal forms.
T or F: Canned foods are shelf stable in a cool, dark room for an indefinite period of time
F: Can keep at room temperature
What is one spoilage organism that home canners should worry about? Why?
Colstridium botulinum.
They are destroyed at high temperatures, but they form hardy spores, that produce a deadly toxin.
How can these hardy spores be destroyed?
Processing in a pressure canner at a temperature of 116C.
What kind of foods need to be processed in a pressure canner
Low acid foods: Meat, vegetables and foods in oil (pesto, garlic in oil or flavoured oils)
They must be processed at a minimum of 116C to kill of the spores
Where should pesto, garlic in oil or flavoured oils be kept? For how long?
In a refrigerator, for 3 weeks
What are some high acid canned foods?
Jams, jellies, marmalades, fruits, fruit preserves, pickles, etc.
What is carrageenan?
A seaweed from the North Atlantic ocean, it has a powerful gelling agent.
What is carrageenan used for?
jams, ice cream, sherbets, condensed milk, instant soup, cakes, cookies and candies. (Acts as a stabilizer, thickens or gels)
T or F: freezer jams don’t require processing. Why?
T.
Freezing (-18C) halts bacteria growth
How do freezer jams differ from regular jams?
Artificial sweeteners can be used, (b/c they are not exposed to high temperatures)
Who would benefit from eating freezer jams?
People who wish to restrict their calorie or sugar intake, people who are diabetic or on weight loss diets
How do low sugar preserves differ from regular jams?
Concentrated fruit juices and artificial sweeteners can be used to reduce/modify CHO content. Spices, herbs or flavourings can increase the flavour.
What kind of fruit is prone to color loss in canning? What can be done?
Lightly colored fruit.
Place in a colour protection solution prior to canning and 5-7 ml lemon juice/ 250 ml canning liquid can be added to prevent discolouration
How does freezing preserve foods?
Halts the growth of surface microorganisms and slow enzyme activity
What occurs when food is frozen slowly? What happens when you thaw the food?
The water in the food form ice crystals which puncture the cell walls. Upon thawing there is drip (loss of liquid)
What occurs when food is frozen rapidly? What happens when you thaw the food?
Allows for formation of small ice crystals. This reduces the drip
How can rapid freezing be achieved?
cool food before freezing in small portions
How does freezer burn occur? How can you prevent freezer burned food?
Occurs doe to the cool, dry air
Packaging should be air tight
Where is thawing the safest? __h /kg of food
Fridge. 10h/kg of food
What are some steps for successful freezing?
SELECT foods of high quality
PREPARE foods quickly and w/ great care
BLANCHING helps preserve color, inactivates surface enzymes, easier to remove skins
PACKAGE in odourless, tasteless, vapour and moisture proof freezer bags
FREEZE at -18C
THAW foods carefully and use immediately
How does drying food preserve?
Uses heat to evaporate water from food. Lack of moisture limits microbial growth.
Why is it important to blanch foods before drying? What are some ways to prevent discolouration?
blanching: breaks skin to allow moisture to escape
Treatment Solutions and Methods:
- Sodium bisulphate solution, salt solution, citric acid or ascorbic acid solution.
- Lemon, lime, orange, pineapple juice
- Jello powder, spices (ex. cinnamon), honey
How should dried foods be stored?
At room temperature in a cool, dark, dry place
Briefly describe how you would rehydrate dried vegetables. When cooking with dried vegetables, when would you salt?
Soak in the fridge for several hours. Add salt near the end of cooking
How much moisture may be left in dried foods?
6-10%
Where is pectin normally found?
In fruit, acts as the cement to hold the cell walls of fruit together. More concentrate in the skin and cores of the fruit.
T or F: Fruit that contain less pectin are more suitable for jam and jelly recipes. Why?
F: fruit that contain more pectin are better for jams and jellies
Because they contain more natural pectin to help gel the jellies and jams.
How can we tell when a jam is ready? (3)
Which one of the 3 is used for jellies?
- The temperature test: Use a candy thermometer. should be 4 C above boiling water temp
- The plate test: Should gel on a frozen plate
- The spoon test (for jellies): the jelly should join as they drop or drop as a sheet, when a cold metal spoon is placed in the jelly.
Commercial pectin is made from
extracting pectin from apple pomace (residue once juice is extracted) or citrus products.
available in powder or liquid form
When using the standard commercial pectin, the product is designed to be used with enough sugar so that the final sugar concentration of the jelly is ___
60%
In little to no sugar jams, what kind of pectin is in there?
This pectin forms a gel without sugar in the presence of divalent ions, like calcium. Contains locust bean gum and xantham gum. An artificial sweetener can be used.
