Friday, September 17, 2010

Food Preservation: Part 1

Daring Kitchen's September Challenge has offered a great instruction file on food preservation through canning or freezing. For the entire month, I have been trying to can my own fruit, with some success (and plenty of failure - some Starcraft induced). They offered an amazing and print-friendly guide and recipe here. Below is a summery of what is in the guide.

While canned and preserved food are readily available in markets, there is nothing more satisfying than doing it yourself. It is especially important for those with their own garden, so they can preserve excess fruit or vegetables. Also, it allows you to control the ingredients for those with allergies.

To preserve food is to prevent:
1. The growth bad bacteria or fungus
2. Prevent undesirable enzyme activities
3. Eliminate oxygen and reduce unintentional moisture loss

FAT TOM are key factors in preserving food
Food: Avoid food with low acid, rich in protein (e.g. eggs) because bacterial thrives on these
Acidity: Acidity prevents enzyme activities and bacterial growth.
Temperature: Nothing like a good boil to kill germs. Freezing at -40F or lower can also kill living things alike.
Time: Even if twinky can survive nuclear blast, it will still expire eventually.
Oxygen: Most bacterial needs air (but some do thrive in the absence of oxygen)
Moisture: Bacterial don't thrive without water or in brine (salted) solution

Brief summary of how each food preservation method works.
Preservation MethodAcid Temperature Oxygen Moisture
Freezing   Storing foods at 0F (-17.8C) or lower Airtight packaging  
Boiling Water Canner (high acid foods)/Pressure Canner (low acid ) Some foods can be acidified using vinegar or lemon juice Heats foods to kill bad bugs and neutralize enzymes Jars form a vacuum seal – creates a low oxygen environment
Pickling and Fermentation Food is acidified by using vinegar or natural bacteria creating lactic acid     Brines (salted water) and sugars reduce fresh water
Drying Airtight packaging Removes up to 90% of the moisture
Jam and Jellies Vinegar or Lemon juice, Fruits naturally acidic Cooking, canning or Freezing Canning will create a vacuum seal Sugar reduces water available

Usually, we don't have the industrial strength freezer that is required to prepare sashimi, but most commercial fridge are old enough -17.8C (0F) to keep food preserved for a long time.
1. Rapid freezing creates smaller ice crystals which expands and puncture cell walls.  This can either destroy food or work in your favour by killing germs.
2. Freeze in small portions, in airtight and leak proof container.
3. Freezer burn is drying caused by airs and gaps in the packaging.

Next post I will talk about Boiling Water Canning.

Click here to go to Part 2

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