Cool Food Storage
Keeping food cool, as we all know, extends the storage life. Ideally,
this means reducing food wastage, and hopefully reducing negative
impacts on the landbase.
In keeping things cool, we want to minimize heat gain to our cooler,
maximize heat loss, and maximize heat storage.To minimize heat gain,
we want to keep our cooler in the shade to avoid heat gains from sunlight.
We also want to keep it away from hot objects - obviously, you shouldn’t
put your icebox right next to your wood stove. Keep it in the coolest
place that you can. Insulation around the cooler is important, since
it stops heat from getting in to warm the food.
There are a few different techniques to maximize heat loss. Evaporation
is an excellent way to carry heat away from your cooler, the way that
sweat carries heat away from your skin to cool you down. Modern refrigerators
use a fluid which is evaporated and condensed in pressurized coils,
which is a variation on this basic idea. Heat can also be carried
away by conduction, such as by a cool stream in which jars of food
are placed, or by cool, moist earth underground. Adding ice is another
way to get rid of heat. The ice cools the compartment, and as the
ice melts, the draining trickle carries the heat away.
Maximizing heat storage, within reasonable limits, is important to
moderate temperature variations that happen because of short term
changes in weather, like cool nights and warm days, or because of
the opening of a cooler door. Cold holes and root cellars use the
thermal mass of the earth itself, which absorbs away extra heat.
We will discuss tools which use all of these approaches.
A note on Food Safety
Without regular, industrial refrigeration, people may be confused
about just how safe different sorts of food are.
Smell food to check for spoilage, but remember that food that smells
fine isn’t necessarily safe.
Fruits and Vegetables: Do not generally need to
be refrigerated, but should be kept as cool as possible. Apples and
some other fruits release a gas (ethylene) which causes ripening,
so many fruits and vegetables will keep longer if kept separate from
apples.
Meats: Large, solid, whole pieces of meat from mammals,
like rump roasts will last the longest. Uncured sausage lacks preservatives,
and may spoil. Chopped, raw meats, like hamburger will spoil quickly,
and should be eaten as soon as possible; even if kept relatively cool,
they may spoil in as little as twelve hours.
Dairy: Hard cheeses will last a long time at room
temperature. Soft cheeses like cream cheese will spoil more quickly
– watch for bad flavour or mold. Unrefrigerated milk spoils
quickly, but sour milk can be used for baking, or to make cheeses.
Custard, gravies, creamed foods, chopped meats, poultry and seafood
sandwich fillings are foods which will spoil very quickly when brought
to room temperature.
Canned food which has been frozen may still be edible, if it looks
and smells good. However, do not taste it! Food from cans which are
burst or punctured should not be eaten. If you do eat food from cans
which are suspect but probably safe, you should still boil the food
for at least 10 to 20 minutes to avoid botulism.
Food Safety Notes:
“Safety of Refrigerated Foods After a Power Failure,”
University of Florida Institute of Food and Agricultural Sciences,
1997.
Water Immersion
A “spring house” is a shed or insulated chest built
over or adjacent to a spring or small, cold stream. Inside, the water
flows through a tray, in which you place containers of food to be
kept cold. A similar system could work at the edge of a cold lake
or river - water could be channelled into the tray, or a covered cage
could be securely placed in the water. Watertight jars are very helpful
in this kind of cooler. Shade will also help on sunny days.
Cold Room
A cold room is just a room in your house which is kept as cold as
possible. It should be on the shady side of the house. I have seen
very effective, insulated cold rooms which have vents that are opened
at night to let cold air in, and closed in the day to keep warm air
out. These cold rooms can be as effective as refrigerators most of
the year in cooler climates, and are much more spacious. An example
is illustrated at right.
In-ground Cooling
Root cellars, cold cellars, and cold holes all use the coolness
of the earth.
A cold hole is simply a well-like tunnel dug down into the earth.
The sides can be secured with old metal barrels, stacked on top of
each other with the tops and bottoms removed. The food is put into
a crate or bucket, and lowered on a rope into the hole, which is kept
covered. It can be as little as a few feet deep, or ten or more, as
appropriate. The depth of the water table is a limiting factor.
A cold cellar, also called a root cellar, is a room built into the
ground often part of a house.
Small scale improvised “root cellars” are actually very
easy to make. If you have an old refrigerator, you can remove the
electrical connections (and anything else you might want to salvage
or keep out of the ground) and bury it, back side down, in the ground.
Leave just a few inches and the door above ground. The shelves form
ready-made vegetable storage compartments. For climates with very
cold winters, pile straw, leaves, or other mulches on top of the “cellar”.
Any large containers buried in the ground can serve the same function.
Try barrels, or garbage cans. However, make sure to keep them away
from moisture and puddles, because you don’t want water to seep
in and freeze the crops, or to freeze the container shut. Make sure
that the container has a top which closes tightly enough to keep out
rodents. And put a deep layer of leaves or straw overtop, to insulate
and keep snow off. You may need to put boards, a tarp, or chicken
wire overtop of the insulation to keep it in place.
If you have access to bales of hay or straw, you can make a wire
or metal box on the ground, to keep out rodents, and stack square
bales around it. You can also line the box with styrofoam or other
extra insulation.
Keep storage fruits and vegetables separate, and they will last longer.
Many vegetables can be stored in root cellars including potatoes,
carrots, beets, turnips, salsify and parsnips. Different vegetables
have different temperature and humidity requirements. Please see below.
Asterisk (*) means short term storage only.
Cold and Very Moist:
(0-5ºC / 32-40ºF and 90-95% relative humidity)
Carrots Beets Parsnips
Rutabagas Turnips Celery
Chinese Cabbage Celeriac Leeks
Salsify* Winter Radishes Kohlrabi Collards* Broccoli*
Horseradish* Jerusalem Artichokes
Cold and Moist:
(0-5ºC / 32-40F and 80-90% relative humidity)
Potatoes Cabbage Apples
Oranges Grapefruit Pears
Grapes* (5ºC / 40ºF) Cauliflower*
Cool and Moist:
(5-10ºC / 40-50ºF and 85-90% relative humidity)
Cucumbers* Cantaloupe
Muskmelon Sweet Peppers* (7-13ºC / 45-55ºF)
Watermelon Eggplant* (6-10ºC / 50-60ºF)
Ripe Tomatoes*
Cool and Dry:
(0-10ºC /32-50F and 60-70% relative humidity)
Garlic (keeps best around 50% humidity)
Onions
Green Soybeans in the Pod*
Moderately Warm and Dry:
(6-10ºC / 50-60ºF and 60-70% relative humidity)
Dry Hot Peppers Pumpkins
Sweet Potatoes Winter Squash
Green Tomatoes (as high as 70% humidity)
Root cellar notes:
An excellent resource is “Root Cellaring: Natural Cold Storage
of Fruits and Vegetables” by Mike and Nancy Bubel.
Ice Caves / Ice Houses
In climates where a significant amount of ice forms in the winter,
or even where a decent amount of snow falls, this technique might
be applicable. Ice caves and ice houses are designed to store ice
from winter for use later on.
Ice caves can be dug into the northern side of hills (in the northern
hemisphere), or a very well insulated shed or shack can be built.
In either case, insulation such as straw is put onto the ground and
between the blocks of ice. You may want to provide a drainage channel
of some sort for meltwater, depending on your design and climate conditions.
Historically, ice was usually cut from bodies of water and dragged
to the storage space. If you don’t have access to a body of
water which freezes over with enough ice, you can pile up snow and
walk on it with snowshoes and boots to tramp it down. Try to compress
it as much as possible, and then leave it for a few hours to solidify.
Then cut blocks and store them as with ice. However, the compressed
snow blocks will not last as long because they are much less dense
(any given volume of snow is 90% air), and probably won’t be
as clean as the ice blocks.
Ice Boxes
An ice box is a simple, insulated box or cooler, into which ice
is placed. The ice will last longer if there is a tube to drain water
away from the ice as it melts. The ice usually has a tray or compartment
at the top of the cooler, if possible, since the cold air sinks down.
Vapour Pantry / Pot-in-pot Cooler
These two techniques work by evaporative cooling, the same way that
sweating cools you down.
You can build a simple vapour pantry by using a (preferably waterproof)
container, such as a small cupboard, or a barrel with an access door
cut in the side. Place a tray of water on top of the container. Affix
the edges of several (damp) towels in the tray, and let them hang
over the sides of the container. The water in the tray will be “wicked”
into the towels, keeping them damp.
The pot-in-pot fridge was recently adapted and popularized by Mohammed
Bah Abba. It’s very simple. Place one pot inside a larger pot.
Fill the space in between them with wet sand (which is rewetted regularly),
and cover the top with a wet cloth. If the outside pot is unglazed,
water can evaporate through it more easily.
Both of these techniques will work best in relatively dry and well
ventilated, preferably windy, areas. You can try putting these outside
(but in the shade) so that they are exposed to more wind. Alternatively,
you can put a device working by evaporation in the wall of your house,
so that you can access the food from inside and protect it from scavengers,
but let the wind outside help with the cooling.
You can also use a system with two buckets, one full of water, and
the other full of food. This can be hung from a (shady) tree, with
the water bucket on top. A cloth is draped over both buckets, with
part of it immersed in the water. It works in much the same way as
the first example above.
Salvaged and Modified Refrigerators
It is possible to modify some refrigeration equipment so that it
does not need to run on electricity, but can run directly off of some
other motive force. I have seen a chest freezer which runs (quite
well) with the compressor running off of a water wheel, using no electricity.
However, this wouldn’t be appropriate for most people, so I
won’t go into any more detail here.
There is another type of refrigerator that would be appropriate for
salvaging. The type of fridge used in RVs does not have any moving
parts, and runs on the heat from burning propane or gas. This type
could be modified to run off of a fire created by wood, biodigested
methane, or any other source of sufficient heat. A fridge working
on this principle could even be solar powered.
For information on RV-type refrigerators (ammonia type) see http://www.nh3tech.org/absorption.html
or a book on refrigeration.
Cooling Notes
The Encyclopedia of Country Living, by Carla Emery.
Fieldbook for Canadian Scouting, Boy Scouts of Canada, 1986
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