Wednesday, August 17, 2011

Reducing the Canning Footprint

I had a minor freak out yesterday when, for a lark, I did a rough estimate of the energy costs of pressure canning.  On a recheck of my calculations I found a major error that put me off by a factor of 1000.  Oops!  After the error was caught I was relieved to find that - provided I started with water brought up to room temperature, and used a bare minimum of water, and ran a full batch through my pressure canner - I could can salsa for about one-sixth of a fossil fuel calorie for every calorie of preserved food.  If you want details about these calculations, find them in the comments.

The larger point is that this got me thinking about the carbon footprint of the food that I preserve.  Obviously, it's more energy intensive than the stuff we eat fresh out of the garden.  Going into freak out mode over what I erroneously believed was an absolute travesty of fossil fuel consumption made me scrutinize the food preservation process as a whole.  How could I whittle down the energy inputs to the food we preserve?  Here's what I came up with:

1. Can local products and minimize use of ingredients shipped from afar.  It makes sense to start with foods that don't have inherently high carbon footprints before they arrive in our kitchens.  Home canned food can only be as energy efficient as the ingredients that go into it.  Obviously, finding a substitute for sugar grown a long way off won't be easy for most people.  But we can opt to make lower-sugar jellies and jams.  It'll be healthier for all of us while also lowering our food miles.  Better still to can what we grow from seeds we start ourselves whenever possible.  Growing your own from seed you save yourself makes you a low carbon footprint rock star.

2.  Switch to re-usable canning lids.  Tattler lids are re-usable indefinitely, and are made from plastic which does not leach BPA - an endocrine disruptor that mimics estrogen.  BPA does no one any favors and is especially bad news for prepubescent children. Re-usable lids will entail a higher upfront cost that may not be feasible for everyone, though I believe it makes good sense both economically and in terms of energy consumption over the long term.  Fossil fuels certainly go into the production of the Tattler re-usable lids and rings, but far more energy goes into the mining of metal for the single-use disposable lids, as well as the BPA-containing plastic lining on those lids.  This is an investment worth working towards incrementally as your budget permits.

3. Prepare large batches so that you max out the capacity of your canner each time you fire it up.  The more food you get out of one run through the canning process, the lower the energy usage per jar.  Check the yields on canning recipes and try to scale up so that you fill your canner each time.  Write margin notes on the recipes you use regarding the accuracy of the stated yields so that you can work more efficiently in the future.  Also, make every effort to ensure that each jar seals successfully.  Each jar that fails to seal and requires reprocessing doubles the energy consumption to preserve that food.

4. Bring the water needed to ambient temperature (or better) before you begin the canning process.  In summer the water that comes out of our tap is roughly 59F/15C.  The canning process takes that water to 212F/100C and beyond.  That's exactly where the bulk of the fossil fuel is consumed - in heating water.  A few hours' worth of foresight can shave off a significant chunk of those fossil fuel calories.  All you need to do is fill the pots you'll need to use in the canning process well ahead of time.  A water bath canner full of 59F water will warm up nicely when placed in the full August sun for several hours.  Even if the pot only sits indoors on a cold stove for a few hours, our kitchen is very rarely less than 73F/23C during the summer months, and often much higher.  If you're more ambitious and better equipped, you could use a camp shower bag to get the water really hot (easily 100F/33C).  It may not seem like these small temperature differentials should make much difference, but heating the water is the major energy cost in the canning process.  Temperature is a measure of energy, and saving energy is the name of the game here.  I know planning ahead isn't the easiest thing in the thick of the summer gardening season, but in this case it's a free and relatively easy way to reduce your energy consumption.

5. As an obvious corollary to the above, use as little hot water as possible when you preserve food.  Leave only the required amount of water in the canner when you're ready to process the filled jars.  Extra water doesn't contribute anything to the process; it only consumes more energy for no purpose.  If you're pressure canning, you can sterilize your jars in the canner with only a few inches of water and preheat the canner in the process.  Just run the pressure canner with the lid on to the point that steam is being produced; you don't need to pressurize it.  Leave the canner closed until you're ready to fill the jars.

6.  If you happen to be blessed with a woodstove to heat your home, and are able to delay some of your canning to the cool months of the year, go for it.  In doing so, you would avoid using any fossil fuel calories at all, and you'd be piggy-backing food preservation on the necessary heating of your home.

Got any other energy-saving tips to do with canning or food preservation?  Please share in the comments!

20 comments:

Kate said...

Some numbers to do with canning:

I ran a batch of salsa through my pressure canner, which holds 16 pints when completely full. The USDA lists "commodity salsa" as having 160 (kilo)calories per pint. Using that figure as a ballpark estimate, I calculate that the value of my batch of salsa is 2560 (kilo)calories.

A calorie is defined as the energy required to raise one milliliter of water by one degree Celsius at sea level. I'm ignoring the altitude for this process since mine is trivial. Starting with a gallon of water at 77F/25C means I need to use roughly 284 kcals to bring that water to 212F/100C. After that the phase change from liquid to vapor requires 2044 kcals per gallon.

Since I estimate that only 10% (at most) of the gallon of water actually boils off as steam, I'll use 10% of 2044 as the additional energy requirements of the canning process. If anyone cares to measure more precisely, I'd love to hear your figures. That gives me an energy requirement of 488 kcals to can 2560 kcals of salsa - when using only one gallon of pre-warmed water at sea level.

That works out to between one-sixth and one-fifth of a fossil fuel calorie per calorie of preserved salsa. If you double the amount of water used, you roughly double the energy consumption.

Of course all these calculations are very rough estimates. The energy figures are for laboratory conditions that will not be reproduced in your kitchen, and they apply ONLY to the canning process, not to any of the embodied energy in the jars, lids, equipment or the food itself.

CTMOM said...

I'd add that you can do batch preserving. I have canned tomatoes, followed by pickles for instance. No additional water usage, the water was still hot, etc. Also, I recycle the metal canning lids so in our home, they are not disposible. : )
CTonabudget.blogspot.com

Tamar@StarvingofftheLand said...

Kate, I love the way you think. I did a similar calculation the last time I made jelly, and it wasn't pretty.

A couple of things. First, if your stove is anything like mine, you've got quite a bit of inefficiency in heating water. When I fire up a burner, I do a lot of heating of the kitchen, rather than the water. Also, you do more than just bring the water to temperature. You keep it there for some period of time. You might be able to get a more accurate estimate by looking at the BTU rating of your burner, and figuring out how long you're running it.

Also, on canning local produce. There have been various estimates of the contribution that food miles make to the overall carbon footprint of the produce, and they're usually in the range of about 10 percent. That 10 percent can easily be made up by efficiency in growing. It's impossible to know how efficiently either your local produce, or produce from afar, has been grown. Sometimes, a green bean from far away has a smaller footprint than a greenbean from your local farm. Maddeningly, we have no way of figuring out when that's true.

I've come to the conclusion that the complexity of the calculation for energy use makes it all but impossible to figure out whether it makes more sense to can or to freeze, to buy local or to buy foreign, or even to try and grow food in a place that requires massive soil amendments to be trucked in.

What we *can* do is simply try to be prudent, waste as little as possible, and never use more when we could use less. Which I think you do better than just about anyone I know.

Anonymous said...

There is also the possibility of using Weck jars: glass bottoms, glass lids, and rubber gaskets. They are suitable for both hwb & pressure canning, and the gaskets are reusable.

(When they eventually do need to be replaced, at least the rubber is harvested from a living tree.)

The come in a wide variety of sizes & styles & I can get at least three layers of jars (500 ml & under) in my canner. (Some styles are very skinny & some are short & flat.)

And they are beautiful. :)

I tend to dehydrate more than can, but for some things (such as meat), I'd rather can than freeze; one-time energy cost.

Also (d'uh), I usually can at night, after work, b/c that's when I'm most likely to have the stretch of time, but CTMom is right - if you can do two (or possibly three) successive batches in one day with the same hot water, the energy spent per jar drops considerably.

saving for travel said...

Thank you for this informative post and great comments so far.

Sft x

Jena said...

Great topic!! You mentioned sugar. I would encourage people to seek out beet sugar versus cane sugar. Here in Michigan many of our neighbors grow sugar beets and the sugar is processed right here as well. It is sold under the names Pioneer and Big Chief. Sure beats that cane sugar crap from South America! :)

timfromohio said...

Wow - great list of suggestions!

For those that use "one time use only" canning lids, you can always use the lids again for freezer jam or freezer tomato sauce - we mark all lids that have been used once in hot water or pressure canning with a black dot or star and then these go into the "freezer-only" stash.

Kate said...

CTmom, good point. I had meant to put that one in, but it slipped my mind. I may add it to my list of suggestions.

Tamar, you're absolutely right about all the other variables that are hard to pin down. This is obviously just a rough estimate. My stove top is a gas range, with four different size burners, all of which can produce flames from tiny to substantial. For me, calculating back from the burner would be pretty difficult. As for efficiency, I agree it's fairly opaque when you are working with purchased food. The vast majority of what I can I had some hand in producing. So at least I have some sense of the energy inputs there. P.S. left you a comment with a video link on your own blog.

Anon, I've never heard of Weck jars. Are those the clamp lid types that are more common in the UK and Europe? I dehydrate some too. Never have run the energy calculations for that though.

SFT, you're quite welcome!

Jena, thanks. I've been opting for organic cane sugar since GM sugar beets were approved in the US. Beets at least are a biennial, so perhaps the GM genes are less likely to spread. But I try really hard to stay away from GM foods, and I figure most sugar beet producers are going to go that route now. In any case, I can't say for sure that beet sugar isn't GM contaminated. Since there is no GM sugar cane yet, I feel more confident about that. But in any case I try to use low-sugar recipes to reduce the food miles.

Tim, thanks. Good tip on re-using the canning lids. I mostly use the lids to indicate which empty canning jars were thoroughly clean before being put back in the pantry area. When it's time to fill them again, I know the ones with lids just need a quick rinse and sterilization. The ones without need more serious attention.

Dmarie said...

I am such a chicken when it comes to really canning foods. I will pour things into jars, let them seal, then stick them in the fridge and use them quickly! if I weren't even MORE afraid of using a pressure canner, I'd probably feel safe eating goods canned that way!! ;)

pelenaka said...

Pressuring canning is my least favorite form of canning so I only do the bare minimum; meats, corn, green beans, carrots. I don't use pressure can my salsa.

I also use an old coal laundry stove on my patio to can with using free firewood. I calculated my cost to be just the lid, water, what ever I couldn't grow or barter for. So generally speaking a quart of stewed tomatoes costs 18¢. Majority of my jars & equipment were either gifted of bought second hand all since been paid off.

Ilene said...

I've always wondered if I actually saved much running a canner with garden produce when it's hot outside and the central air is cooling the house. I don't have a "canning kitchen". I really liked the tip about setting the water out in the hot sun. We have buckets we use in the garden, it would be easy to clean them out enough to hold clean water and heat up a day's worth of canning water. I'm probably not very good about using the bare minimum of water when pressuring because I've always worried about the canner boiling dry.

Glad you mentioned dehydration. I have a walk-in attic with an insulated door between it and the rest of the house. I have not used my electric dehydrator since we moved here. I just place my slices on the dehydrator trays and carry them up to the attic. They're dry and ready to pack up in a day or two.

Oh, and if you need to treat fruit with ascorbic acid, use crushed Vitamin C tablets that are sold as daily supplements. Much cheaper than stuff marketed for that purpose. When crushed, they break down quickly in water.

Jennifer Montero said...

I've tried reusing old jam jars with wax / cellphane lids to process my jam but I was getting a lot of spoilage. I've sourced some Ball jars with replaceable lids so I hope my preserves will stay fresh. Food lost to cutting corners is a waste (the chickens don't think so - they're going to get diabetes from the amount of crabapple jam they're eating)

I'm a freezer advocate. I've already got it running for meat etc and the fuller it is, the more efficient it is. Especially, if like us, you get power cuts throughout winter. Some things freeze better than other, so they get priority.

I use mostly 'free', or homegrown foods for jams and chutneys but I never considered the sugar miles. Has anyone made jam from beet sugar? Any good?

I will also be leaving the water to room temp before I start - good tip! Small but easy to do, and effective. Thanks Kate!

Hazel said...

Jennifer: You've probably made jam from beet sugar.

In the UK, most white sugar is made by either Silver Spoon or Tate and Lyle. Silver Spoon comes from UK (non GM so far) sugar beet whilst Tate and Lyle is made from (fairtrade) sugar cane. I buy either according to where I'm shopping, and have never noticed a difference.

I'm interested that you have such a high spoilage rate with your jam reusing lids. I also reuse regular jam jars for jam and chutney and don't have a problem.

I'm assuming that the standard British advice that it's the same thing as penicillin and therefore good for you is not what you want to hear! (My friends mother, who was positively tight- way beyond frugal- used to tell her to stir it in. At least my mum would scrape the mouldy bit off!)

I think that the dinky wax discs and cellophane covers may make the problem worse, especially if the packet has been opened and left hanging around in a drawer- I did have one year where several jars had mouldy tops. I gave up the wax circles, just making sure I sterilised the lids and it's been fine ever since.

Thanks for an interesting post Kate. DH always says it's the initial heating of water that takes the energy. Prewarming it is is so obvious once you say it. Our central heating boiler is in our utility room and gets quite warm (I use it for yoghurt, drying clothes etc). I bet I could warm it significantly on there.

Kate said...

Dmarie, I guess my intro to canning was trial by fire, because I used a pressure canner before I ever tried the water bath method. I feel safe using it because I know what precautions to take and maintenance to do.

Pelenaka, I would prefer not to pressure can salsa either. But the recipes I've found for water bath salsa add so much acid that I find it unpleasant to eat. If you have a good WBC salsa recipe, please share it! Outdoor free firewood canning sounds awesome. Color me jealous!

Ilene, I try my hardest to can when the temperatures dip a little bit. We're enjoying positively cool weather (for summer) here at the moment - a welcome respite from the heat waves of June and July. Passive dehydration works well if you're in a relatively dry place. Generally our summer humidity is too high for that to work where I am. Thanks for the ascorbic acid tip!

Jennifer, I agree that food lost to spoilage is a crying shame. I've had pretty good luck with these Tattler lids so far. If I had more freezer capacity, I might rely more on that for summer produce. But on the other hand, knowing how things have gone with our one chest freezer, I might just fill up a second one with all sorts of other stuff. As for the differences between beet and cane sugar, as Hazel intimated, they're insignificant and basically undetectable in kitchen practice unless you happen to be a patissiere boiling sugar syrup to the hardball stage or beyond. In that process there are very minor differences. Unless otherwise noted, white sugar commonly sold in the US is now beet sugar, and probably GM.

Hazel, thanks. Sounds like pre-warming on the boiler is the way to go for you then. Our furnace doesn't run in the summer, and even if it did, it's downstairs at the far end of the basement. Quite a deterrent to carrying a heavy pot of water down there. Our houseplan is such that it's less work to carry a pot into the sunlight.

Hazel said...

I didn't know that about the hard boil stage- good job my sweet making ambitions finish at fudge!

My boiler is on for the hot water by the way, just in case you thought I was profligate enough (or England is cold enough!) to have my heating on in August! DH and I have had extensive...debates...about when the timer should be on, and currently there's a compromise with the hot water timer being off in the middle of the day.

In the meantime (ie, until I persuade him I'm right) I make the most of any radiant heat.

Hazel said...
This comment has been removed by a blog administrator.
eatclosetohome said...

Thanks for the data! And I don't know why I'd never thought about pre-heating the water in the sun before - that's simple and effective...simply brilliant. Thanks for the tip.

I will be experimenting in the next couple weeks with a self-contained electric water bath canner. I got it to expand stove capacity at large Preserving Traditions canning events, but I'm curious to see if it's more energy-efficient than canning on the electric stove. The heating element is totally contained, and I assume runs around the sides and bottom, like a crock pot, which will deliver more of the heat directly to the water. It should certainly keep the kitchen cooler. I plan to measure energy usage via the electric meter - not too precise, but will at least give an estimate. My guess is it wouldn't be worth it to get one if you have a stove and canning equip (too much embodied energy, plus shipment from Europe), but we'll see. On the other hand, compared to installing a new stove at the Grange, it's a bargain.
Emily

Kate said...

Hazel, no worries. I wasn't judging your energy usage.

eatclosetohome, anytime! The self-contained canner sounds like a neat gadget, though as you say, probably superfluous for most people with a stovetop. I'll be curious to hear any figures you come up with in comparing its energy usage to other methods of canning.

veronica said...

hello, i am new here. I found your blog when i typed into google"waterbath canning energy use" When my canner is going full blast I cringe to think of the watts powering my electric stove. Thanks for the notes and tips/ Its reassuring. O was wondering about a pressure canner, for things that are usually done in a waterbath...is that more efficient. I don't have one but havedone some research and looked at them in the thrift stores.

Heres an energy tip: I keep my freezer in a small insulated space and the heat from the motor keeps the space warm enough that it is just right (in our northern climate) for fermenting pickles, kimchee, cider vinegar, wine, etc...

Anonymous said...

Note on beet sugar. 99% of beet sugar is now GMO per the National Beet Sugar Growers Assoc.