DRY ICE/WET ICE EXPERIMENT FOR COOLER PACKS in the BWCAW

April 14. 2011

DRY ICE/WET ICE EXPERIMENT FOR COOLER PACKS
IN THE BOUNDARY WATERS

Submitted by Michael Termini and Brian Codd
With the great assistance from Piragis Northwoods Outfitters


While we have a bit of experience as canoeists, hunters and campers, this is our first trip to the Boundary Waters.  Over the last year, we have read all of the books and studied the maps, selected our route and then selected our outfitter, Piragis Northwoods Outfitters for our partial outfitting and their advice.

When we have time, after a hard day in the wild, we enjoy a gourmet meal on a par with a fine restaurant, complete with all of the complexity of a great meal.  We have found that we are going to consume 2500 – 3500 calories a day no matter what we eat in order to replenish the body stores expended in the day of travel.  We are willing to carry a little more weight in packs for another pot or two to make those great calories!  So for us, the excitement of the Boundary Waters is only enhanced by the gourmet meals we hope to be enjoying at the end of each day.  But, with the lack of refrigeration for a 5 day trip on the BW, the new challenge was how to do it.

In addition to the general question of how to create refrigeration for 5 days, there was also the issue of the bears and whether a bear cooler was the way to go or whether it was better to hang a pack.

To help answer these questions and figure out what was best for us, our friends at Piragis Northwoods Company and Drew Brockett graciously agreed to let us borrow their big Cooke Cooler Pack and a 30L bear barrel for a couple of weeks during the off season to conduct our experiments and try and figure this out.

This article is a summary of our experiments.  We hope this information helps you plan the refrigeration aspects of your trip.

In reading all of the books on food in the BW, we note that many people enjoy a frozen steak on Day 1 of the trip and let it thaw during their first day of travel and then switch to non-refrigerated foods.  The question we wanted to answer was whether using a combination of dry ice with frozen blocks of wet ice would give us refrigeration for 5 days so we could enjoy more complicated high end meals.   

Wet ice in a frozen block in an insulated cooler will last about 18 hours depending on the ambient temperature outside the cooler and how often the cooler is vented through the day.  Without a different solution, this would mean that we would be consuming traditional BW foods from the second day out.

Dry ice has a temperature of 109 degrees below zero.  So the theory we wanted to test out was whether we could use the colder temperature of dry ice to extend the life of wet ice and maintain an effective freezer/cooler for the duration of the trip.

The short answer to the question is yes, as long as you are willing to make the tradeoff in a bit of extra weight for your trip in portaging. 

We conducted 2 experiments.  For the first experiment we used both the bear cooler and the Cooke Cooler Pack.  For the second experiment, we used only the Cooke Cooler Pack. 

For the containers for wet ice, the thinner plastic of a milk container suggested the possible risk of an accidental puncture.  The gallon containers from canola oil or juice containers are stronger than traditional milk containers and are not significant in the overall weight difference, so the thicker containers became the preferred container.

When freezing these containers, remember that water expands when it freezes, so leave 3 fingers or so open at the top to permit freezing expansion.  It took about 5 hours for the containers to freeze, but we elected to allow them to freeze a full 24 hours.

We purchased 8 lbs of dry ice ($1.29 lb) and then split the ice into 2 four pound blocks.

The dry ice was wrapped in newspaper and placed at the bottom of the 30L Bear Barrel and the Cooke Cooler Pack.  The dry ice was then straddled with the frozen containers of wet ice.  So each cooler then had 4 lbs of dry ice, and 12 pounds of wet ice.  Figuring 1.5 – 2 lbs of food per man per day for the 5 days, 9 pounds of meat was then added to the containers, with 3 lbs of chicken, 3lb pork tenderloin and 3 lbs of turkey tenderloin.  We also packed assorted vegetables like salad in a bag, celery, cauliflower and leeks.  This was not meal planning per se but just to get a sense of the how the different densities of different proteins and vegetables would respond in this environment.

Bear Barrel
Day #1 - Sealed the container at 3:00 pm.

Day #2 – At 12 noon on Day 2, the smaller pieces of dry ice had subliminated (evaporated).   By 4:00 p.m. the wet ice was thawing and meats were beginning to thaw.

As Drew at Piragis reminded us, the Bear Barrel is only an uninsulated barrel.  It does have the option of a cooler pack that can fit inside.  The cooler pack is about the size of what you might think of a small picnic basket ice pack and we did not think the pack would suit our needs so we did not use the inner pack in this experiment.

Cooke Cooler Pack
Day #1 - Sealed the pack at 3:00 pm.

Day #2 – At 5:00 p.m. on Day 2, the smaller pieces of dry ice had completely subliminated (evaporated).   The wet ice had thawed about ½ way in containers. 

The chicken was still rock hard frozen.  The meats were very cold but also beginning to thaw.  The vegetables were still all very cold.

So 4 lbs of dry ice lasted almost 24 hours and the additional with 12 lbs of wet ice in the Cooke Cooler, lasted another full day for a total of 2 full days of refrigeration.  The frozen chicken would have taken another half day to thaw.

LESSONS LEARNED:  


There were a few mistakes made in this overall set up for Experiment #1. 

The dry ice was not sealed tight enough.  These packs were maintained in my house at 72 degrees to try to duplicate the expected ambient temperature in the BW, and they were moved around a bit as they shared the kitchen space with the family so the packs were jostled as they will be in the bush. The dry ice came loose from the newspaper envelope in the bear barrel and appeared to subliminate faster.

During this first experiment we found a dry ice web site that recommended that the best way to use dry ice for cooling is to place the dry ice on the bottom of the container with the food items on top.  However, for freezing, the recommended placement process is to place all frozen items on the bottom of the pack and then place the dry ice on top.

Conclusion: 

The Bear Barrel will work well for shorter periods being able to use the cooler pack to fit inside and with a need for a smaller volume of material.

The Cooke Cooler Pack will work well for creating both a freezer and frig, but needs more dry ice to make it for the longer period.

Experiment #2

For Experiment #2, only the larger Cooke Cooler Pack was used.

Based on the first experiment and the new information, we wanted to see if we could create two separate compartments within the cooler pack.  In this way, there would be the freezer half on the bottom section of the cooler allowing the dry ice to sit on top of the frozen items and allow the heavier cold air to sink and the top half of the cooler to act as a refrigerator.

The first issue then became safety and the ability to handle the dry ice during the period that it was subliminating.  With a temperature of -109 degrees F, the worst thing that could happen would be a burn to someone’s hand the first 2 days of the trip. 

To create a safe barrier, we used an 8” x 8” flattened but still put together cardboard box, (but any stiff cardboard will work for this set up).  The interior of the cooler pack was then traced on the cardboard and cut the cardboard to fit as a flat partition into the pack.  We then sealed 3 sides of the cardboard “envelope” with 2 layers of duct tape.  Inserted into the cardboard envelope was 11 pounds of dry ice in a single layer and again double sealed the opening.  The result was a simple and cheap but safe way to handle the dry ice without fear of being burned getting in and out of the freezer.

Knowing we would be getting in and out of the cooler, we labeled the cardboard with directions of top, front and back to indicate the easiest way to make the partition fit back into place.  In this way, whoever is taking items out of the freezer could minimize the amount of time that the bag was left open to the air.

The cooler pack was then packed with all of the frozen items at the bottom of the bag with the wet ice and then placed dry ice partition on top.  In the freezer section, it was loaded with a 3 lb pork loin, a 2 lb turkey loin, a whole 3 lb chicken, 1lb lamb stew meat, 1 lb pork chops and 1 lb ground beef, along with 1 gal wet ice block and 1 quart ice block.

Loaded on top in the refrigerator section were lettuce, milk, butter, celery and leeks.

Through this process we checked the temperature and the contents of the load in the approximate times of meal times to duplicate the opening and closing of the cooler bag in the bush.

Day 1

9:00 a.m. Loaded the cooler pack.

4:00 p.m. Dry ice envelope had shifted out of whack and tilted.  All still frozen and cold, but lost the effect of the freezer vs. frig.  Need to repack tighter.  Also, make sure the milk top is tight in case load shifts during portages.  Repacked load.

Day 2

6:00 a.m.  Dry ice has subliminated by 3/4s.  All items in freezer compartment remain frozen and cold on top.

4:00 p.m.  Dry ice was fully subliminated but still very cold in freezer section and bottom of cardboard envelope has ice on it.  All frozen items were frozen and refrigerator remained very cold.


Day 3

7:00 a.m.  Dry ice had fully subliminated and envelope was no longer cold.  Wet ice remained frozen.
Pork chops beginning to thaw, but still frozen.
Ground pork fully thawed
Lamb stew meat still frozen but beginning to thaw.
Whole Chicken- still rock hard frozen.
Pork Tenderloin – very cold but almost thaw.
Turkey Tenderloin – cold but thawed.

In the refrigerator:
The celery was ruined.  It was totally wilted and looked like it got freezer burn.
Lettuce- one package became totally wilted and a second package of lettuce remained cold.
Milk had lost some temperature from the prior day.

Repositioned all items and now treating the entire cooler pack as a refrigerator and repacking with wet ice.

6:30 p.m.
All items still very cold.  The refrigerator is maintaining the temperature.
Chicken still frozen but beginning to thaw.
Wet ice still has ½ ice so it is maintaining the cold temp in the refrigerator.

9:00 pm
The second bag of lettuce went to totally wilted.  It may have been placed too close to the frozen items and just got too cold. 
All other items are still very cold. 
Whole chicken is thawing but cooler remains very cold.
Milk is still cold. 

Day 4 - 8:00 a.m.

All items still remain very cold. 
Wet ice has melted in quart container but still cold. 
Wet ice in gallon container has almost melted but still very cold. 
Chicken is thawing but still very cold and has a ways to go. 
Milk remains very cold.

5:00 p.m.
All items are still cold, but all but chicken has thawed.  Milk is still cold.
Melted ice water is still very cold.



Day 5 – 8:00 a.m.
Chicken is thawing but still very cold; would need to be consumed today.
Water and milk are dropping in temperature so need to be consumed.


Lessons Learned:

Keeping the bottom layer packed well so that the dry ice envelope says in place on top. There is sensitivity to getting in and getting out of the cooler quickly to maintain the temperature.  But taking a few extra minutes to repack and reposition items in the pack to maintain the freezer/refrigerator integrity will be well served.

Create a barrier between the more fragile greens like celery and lettuce from both the dry ice envelope and even the wet ice.  They do not need as much of the cooler temperature to keep them fresh and the more harsh cold ruins them.

One item we are sure we will miss is ice water.  We will have to resist the temptation to drink the ice water in the cooler as it is clearly maintaining the cold temperature inside the cooler.

As far as a boost for refrigeration, the whole chicken should be viewed as “your friend”.    Not unlike the big turkey that takes 5 days to thaw in the refrigerator at Thanksgiving, the chicken as a whole carcass is really an additional solid block of ice that has served to maintain the temperature as the last item to thaw in this overall process.  We will likely plan the chicken as the 4th day dinner meal and then have dry cured meats like ham on the 5th day.

Based on all of the information gained in these experiments, we will definitely take on a bit of extra weight to be able to enjoy a freezer/refrigerator combo in order to prepare more complicated meals.