A bit of preservation – freezing

I hated canning time when I was growing up.  Hot, messy, labor intensive for canning and saltpacking and drying and freezing and…  I suspect I’m going to hate it when I start doing it as an adult, too, but at least I’ve been there before and know a couple of the pitfalls.  And I will be canning and much of the rest of the various types of preservation.  Thing is, doing a bit of refresher among the intertrons taught me that there are a lot of people who don’t understand what’s going on.  And, I’ll admit, a lot who do.  But I thought, well…

Today’s longwinded post is an introduction to preservation with a few bits of more detail.  And to start, what the heck is preservation of food, anyway?  Answer – obvious but important – is to extend the time between harvest and spoilage of food.  Spoilage comes in two versions.  First, and always important, is unhealthy – causing illness and death.  Second, and with an importance that depends on how hungry you are, is “tastes bad”.

You know?  There’s a specific type of preservation that can demonstrate this second easily, because almost everyone in the US has run into it.  The preservation is freezing, and the “taste bad” spoilage is freezer burn.

Freezing food slows down and in some cases stops bacterial activity.  Bacteria are the primary reason food goes bad.  (In some dishes it’s chemical interactions – like oxidation.  We’ll come back to that.)  Frozen food lasts, therefor, but it does not last forever.  And the reason is subtle.  See, even though it’s frozen, the water molecules can sublimate out of the food and into the surrounding atmosphere.  It’s an osmosis kind of thing…  ok, let’s be a bit more descriptive.  Given a wet thing and a dry thing stuck next to each other, the dry thing will pull water from the wet thing till each are more or less equally wet.  This is true whether we’re talking paper towel against a coffee spill, or dry air around a frozen steak.

Now as a bit of an aside, what’s happening to the food that’s losing water is it’s becoming freeze-dried.  This isn’t always a bad thing, but it’s important to remember it tends to affect texture, and tends to not be restorable.  So when you freeze-dry a piece of steak, it begins to look and feel like a piece of leather.  And you aren’t going to be able to turn that leather into a piece of steak ever again.  However, you can use it as a base for something beef flavored – something that breaks down the beef.  Like a stew, perhaps.  Or as lumps in a gravy – as you find in Chipped beef on toast.  Yes, chipped beef is dried beef, and one way to make it is to freeze-dry it.  And freezer burn is freeze dried whatever.  Except….

If you’ve ever tried to eat something that was freezer burned, you almost certainly had another problem besides the texture.  That’s the taste.  It tasted, well, nasty.  The reason is because when the whatever was losing moisture, it wasn’t a one-way street.  Other molecules – molecules with taste – were coming back to the meat.  The moisture loss is something of a two steps foward-one step back process, and that one step can carry other stuff with it.  So you’re also getting the taste of everything ELSE that’s losing moisture.  Not just the food, mind you, but the shelves that have some frost on them and the walls and …  yeah.  Yummm, aluminum flavored beef.  sigh.

And yet (back to the point), the freezer burned stuff is (probably) not going to be unhealthy.  Probably depends on WHAT molecules got brought.  If your shelves are carrying unhealthy chemical surfaces, you might have a problem.  But I digress.  Knowing everything we have above, we have an answer to freezer burn, and in consequence we can make frozen food last LONGER.  There are two things to do, both focused on preventing moisture from leaving (and secondarily from allowing other moisture to come in).  Simply stated, we want to seal against temperature and we want to seal against vapor.

Now temperature needs a bit more discussion.  See, while the moisture will sublimate (go directly from solid to gas without passing through liquid), the speed at which it does varies with temperature.  The closer the surrounding air is to being above freezing the faster the sublimation.  To rephrase, a freezer that’s frequently opened and so averages 28 degrees F will have food go bad faster than the one which sustains 0 degrees F.  We’re not going to buy a new freezer, of course, but we can do a few things.  One is to keep the door closed as much as possible.  Another is to use a temperature holding mass as the wrapping.  Butcher paper works surprisingly well.  So does aluminum foil.  The latter is a lot easier to get.  So wrapping your soon-to-be frozen goods in foil will help delay freezer burn.  But foil’s not very good at stopping vapor.  Fortunately there are other ways.

Good plastic wrap will make a vapor barrier.  By good I mean it seals well and doesn’t ‘breath’.  Again, butcher paper does this due to the surfacing.  Various ziplock bags also work – though they work better if we try to minimize the amount of air in the bag.  Vacuum bags are great at this.  The problem with plastic is it’s a lousy temperature barrier.  Which is the hint to the solution.

Double seal.  Foil AND plastic.  Now, if the food is acidic you should compromise and put the foil on the outside of the plastic as the acid – even at frozen levels – will eat into the aluminum (and transfer taste…).  But with that exception, you get maximum effect by putting the metal against the food and sealing THAT into the plastic.

By the way… if you’re buying a freezer, there are a lot of really good reasons to buy a chest-type instead of a standing freezer.  The two biggest reasons NOT to do so are the difficulty and danger of reaching deep over the side, and the footprint it uses.  But if you’re going to have a lot of food for a long time, remember cold sinks and all the advantages therein.  I have an upright.   It’s not the end of the world.  It’s just something to keep in mind.

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