I’ve just been taught a first-hand lesson in why hardware stores sell 30% acetic acid (vinegar) as weed killer. That’s because regular household-strength (5%) may or may not work.
Here you see a section of my driveway, sprayed yesterday with vinegar (4%). It’s now a mix of dead and clearly undead weeds.
This post is about killing a whole lot of weeds growing up through a long stretch of poorly-maintained asphalt driveway. Options considered include:
Commercial weed killers (Round-Up, Spectracide).
Vinegar
Salt
Mechanical (weed whacker)
Heat.
Propane weed flamer
Electric heat gun
Boiling water
Steam
Solar, up to and including solar oven
This post is just about gathering the facts, trying to make my mind up. I haven’t really tested any of these yet.
Arguably the biggest revelation (to me) is that several of the alternatives (e.g., vinegar, heat) are really no different from using a weed whacker. It took me a while to figure that out, but all they do is take the tops off the weeds, leaving the live roots intact. That’s just a roundabout way of doing what a weed wacker does directly. In which case, it’s hard to argue in favor of some D-I-Y approach, when there’s a tool actually designed for the job.
After a false start with vinegar, I’ve decided to go with heat. Primarily a solar approach, which seems to fit my situation well. It’s an approach that isn’t typically used so there isn’t a lot of information out there on how well it works. It’s plausible that I can amp it up enough to kill the roots. Plus, I already have the materials on hand to try it.
To cut to the chase: Copper versus citric acid. That’s what I’m going to test this year, for control of powdery mildew on cucurbits.
This post shows how I got to this end point, from my original plan of a formal test of several “home remedy” approaches to controlling powdery mildew.
Using citric acid to control powdery mildew was news to me. There are, however, at least two commercially-available mildew-control products that are little more than a dilute solution of citric acid. Roughly one-twentieth the strength of typical commercial lemonade. So that’s surely worth testing. Continue reading G22-039: Powdery mildew products, Amazon search, and a change of plan.
The American penchant for ignoring the rest of the world never ceases to amaze me. And so, after reading my N-hundreth story about U.S. inflation rate — with nary a whisper about the rest of the world — I felt motivated to blog about the elephant in this particular room.
Much of the reporting on U.S. inflation is fundamentally idiotic. It’s noise generated for political advantage, with no content. It’s all about exploiting an opportunity for finger-pointing. It lacks substance because all of that reporting assumes there’s some unique U.S. cause to our unique U.S. inflation.
I was going to invest maybe a whole ten minutes in looking up the current inflation rate in selected countries. But this is the age of the internet. Maybe somebody put all that information in one convenient place.
So that, if for some peculiar reason, you, as an American, actually wanted to know what the inflation rate was in countries other than the U.S.A., you wouldn’t even have to search for it. Just look it up on the Financial Times website.
This takes the drama out of doing this one country at a time, but it gets right down to the bottom line. Here are graphs of the inflation rate in the U.S., North America, Europe, Asia (other than China), and the world as a whole. (I exclude China because they don’t have a credible domestic inflation measure.) These are all taken from the Financial Times website.
Notice anything?
Now it’s time for Occam’s Razor. On the one hand, maybe each of these countries has some unique, specific factors boosting their individual rates of inflation. Simultaneously.
Or, just maybe, something has happened world-wide, to cause prices to rise. But it’s so tough to imagine what could possibly account for an increase in inflation in almost the entire industrialized world. It’s not as if these countries had anything in common over the past couple of years.
In any event, this is why I’ve had my fill of U.S. reporting on inflation. It’s just so damned dumb. The endless blather about why it’s due to this, that, or the other uniquely American factor. The constant drumbeat of whom to blame for it. But mostly, the absolute unwillingness to take five minutes, look around, and note that this is not an American issue, it’s a global phenomenon.
In terms of the number of dollar bills you must surrender to purchase one gallon of gasoline, sure, gas is now at an all-time high within living memory.
But, as an economist, I have to point out that a dollar isn’t a dollar any more. It used to be worth quite a bit more. And because of that, it’s just plain stupid to look at long term price trends — or all time highs — in nominal dollars.
The vacuum sealer is that rare device that serves as both a kitchen appliance and a source of entertainment. Every time I run my new Nesco VS-09, I practically want to applaud when it finishes.
I don’t normally give much thought to air. Until it’s all gone. Then the arithmetic of 15 pounds per square inch leads to the realization that this goofy little countertop appliance generates a literal half-ton of crushing force on a 6″ x 10″ pint-sized bag.
But I digress. I actually bought this for the serious purpose of preserving garden produce. The fact that I find the process and results to be so entertaining is just icing on the (perfectly flat half-inch thick piece of) cake.
In any event, there is a serious purpose to this post. And that is to show that if you have a freezer that’s already running, then freezing your tomatoes is by far the most energy-efficient way to preserve them.The only method that would beat that is solar drying, and I haven’t quite figured out how to do that well in my humid Virginia climate.
Tomatoes as freezer free-riders.
The last thing I need is another kitchen appliance.
But I bought this vacuum sealer anyway, after thinking through all the food preservation I did last year. Of all the pickling, canning, drying, and freezing, by far, the tastiest, most garden-fresh results came from freezing. With drying (dried tomatoes) a close second, due to the intense flavors that produces.
And so, purely from a quality standpoint, for tomatoes to be used in soups and stews, my wife and I agree that freezing is the best option. It preserves that fresh tomato taste. But how does it stack up in terms of energy use?
Freezing gets a bad rap,as a means of home food preservation, for its relatively high energy use. But I think that’s not entirely correct.
If you run a freezer expressly for the purpose of preserving garden produce, then, sure, I’d bet that freezing has a fairly high energy cost. In that case, you’d have to pro-rate the annual electricity use of that freezer over the pounds of produce preserved. (Because, by assumption, you wouldn’t be running that freezer if you weren’t using it to preserve your garden produce.)
Just tossing out some round numbers, based on past experience, I’d bet that a typical 15-cubic-foot chest freezer has enough space to store 300 pounds of produce, and consumes about 300 kilowatt-hours (KWH) of electricity per year.
So, roughly speaking, if you run that freezer because you use it to preserve your produce, you’d consume about 1 KWH of energy for every pound of produce preserved.
By contrast, if you are already running a freezer, and will continue to run it regardless, and you have the space, then freezing your produce only costs you the energy needed to freeze it in the first place. The cost of running the filled freezer doesn’t count, because you’d bear that cost in any case.
My fridge comes with a big freezer. It’s not like I’m planning to unplug that any time soon. And so, I’m perfectly happy to let my frozen garden produce be a free rider here — taking advantage of the fact that the freezer is running, but not being asked to “pay” for it.
In that case, the only additional energy cost is the cost of getting the room-temperature produce down to the 0 F temperature of the freezer. Given that (e.g.) tomatoes are 94% water, that’s more or less the energy required to bring one pound of room temperature water down to 0 F. Including the one BTU per pound required to cool the water, and the 144 BTUs per pound required to convert to ice, that works out to (70 + 144 =) 214 BTUs, or (at 3.4 BTUs per watt-hour) 63 watt-hours. So, if you are just tossing your produce into a freezer that is going to be running in any case, freezing it takes0.063 KWH for every pound of produce preserved.
You might think that’s a bit of a cheat, because one way or the other, you’ll want to peel those tomatoes before you use them. The most typical methods for peeling them involve heat (either boiling water, or holding them in the flame of a gas stove). But — surprise — it’s actually a snap to peel them after they’ve been frozen, per this YouTube video.
Take a look around 47 seconds into that video. My jaw dropped just after the tomato did. I know the term life-changing is overused, so let’s just say this was a tomato-life changing revelation for me. As in, I’m never going blanch and peel a tomato ever again. Arguably, it may actually take less energy to freeze-and-peel than to blanch-and-peel, what with the energy costs required to boil the water and cool the tomato afterwards.
Other preservation methods
I have already tracked the energy costs of preserving by canning or drying, in various earlier posts. Let me bring all of that together in one place, below.
Drying tomatoes in my four-tray Nesco dehydrator consumed 8 KWH of electricity (per Post G21-049). That was in the humid outdoor Virginia summer. I am fairly sure that each tray can hold less than a pound of quarter-inch-thick tomato slices,, but a) I could stack up to 12 trays at a time for drying, and b) those were very “wet” slicing tomatoes, not the paste tomatoes that are normally used for drying. That said, for illustration, let me just assume one pound per tray, four trays, yield 2 KWH for every pound of produce preserved.
Canning tomatoes in a water-bath canner consumes a considerable amount of energy as well. I did the full workup on the energy cost of home canning two years ago, in Post #G22. I had to do that because, as far as I can see, the rigorous research literature on this crucial topic looks like this:
In any case, the all-in energy cost for canning five quarts of pickles, on a gas stove, in an air-conditioned house, was 5528 kilocalories (kcal).
Per the USDA guide to home canning, quarts of pickles require a much shorter processing (boiling) ,time (15 minutes) compared to quarts of tomatoes (45 minutes) in a water-bath canner.
Based on my prior calculation (shown above), I need to add another 800 Kcal to account for that, bringing the total up to 5300 Kcal for 5 quarts (= 10 pounds) of tomatoes. At 1.16 watt-hours per kilocalorie, that works out to be 0.6 KWH for every pound of produce preserved.
I should note that this is a little conservative, because you have to peel the tomatoes first. That’s going to involve a little additional boiling time. But with all the boiling that’s taking place with the canning, I figured that was more-or-less rounding error.
Finally, I can take a rough guess at the energy cost of my crock-pot spaghetti sauce. Crock-pot spaghetti sauce (Post #G21-048) absolutely minimizes the labor input, and is idiot-proof to boot. But it requires processing tomatoes in both a pressure cooker (briefly) and a crock-pot (overnight). For four quarts (eight pounds), the crock-pot portion uses about 4 KWH. But the pressure-cooker portion (20 minutes at pressure) likely used almost as much energy as canning, so for four quarts I need to add one-third of my pickle canning estimate above, which, by the time all the arithmetical dust has settled, adds another 2 KWH. Or a total of 6 KWH for 8 pounds of tomatoes, or 0.75 KWH for every pound of produce preserved.
Edit, fall 2024: In hindsight, that’s much more energy-intensive than a more traditional reduce-it-on-the-stove approach to making tomato sauce. A crock pot is, in fact, a terrible (but idiot-proof) choice if you want to evaporate water out of a sauce. I’ve gone back to making my spaghetti sauce by boiling down tomatoes on the stove, like a normal person. I still briefly pressure-cook, dump in a strainer to remove the liquid, pass the solids though a Foley mill to remove the skins, then reduce. This allows me to use all types of tomatoes, including salad and cherry tomatoes, without having to peel or seed them first.
There’s no additional energy cost for peeling in this method, because the entire batch of tomatoes is run through a Foley mill after pressure-cooking. That takes out the peels and (most of) the seeds.
Let me now produce the nice neat table of energy required for food preservation, all of it expressed in terms of KWH of energy per pound of produce preserved.
All of that comes with some caveats. The canning was done on a gas stove in an air-conditioned house. The drying was done outside, in humid air. I could dry up to twelve trays at once, instead of the four that I already owned. Maybe there’s a little more energy required for the blanch-and-peel step in some methods. And so on.
Nevertheless, the results are so clear as to be undeniable. (So clear that I double-checked that freezer math a couple of times). If you have space in your freezer, and you’re going to run that freezer anyway, by far the most energy-efficient way to preserve tomatoes is to toss them in the freezer. And, per that YouTube video above, peel them as you thaw and use them.
I surely need to mention the one common method that isn’t on the list, solar (or open-air) drying. Plausibly that has zero energy cost, but I have not (yet) figured out how to do that in my humid Virginia climate. I’m already working on how I’m going to improve my simple $18 plastic-tote food dryer (Post #G21-049). The solution might be as easy as “don’t overload it”.
Two minor caveats: COP and GHG sold separately.
Two minor factors make this conclusion somewhat less that complete. Those are coefficient of performance (COP) of a freezer, and the different rate of greenhouse gas (GHG) emissions for natural gas and electricity used in the home. Near as I can tell, neither of these results in any material change in the relative efficiency of the various preservation methods.
First, this calculation isn’t complete because it doesn’t factor in the energy conversion efficiency or coefficient of performance (COP) of refrigerators or freezers. The coefficient of performance for a heat pump is the amount of heat energy it can move, for a given amount of electricity supplied to it. Almost all commercially-used heat pumps have a COP greater than 1.0. That is, they can move more than 1 KWH of heat energy for every KWH of electricity they consume. COPs for modern AC or heat pump units typically run around 2.5 to 3.5 (per the link above).
The estimate above — 0.063 KWH — is the amount of heat that needs to be (re)moved from the interior of the freezer. It will actually take less than 0.063 KWH to do that, because fridges and freezers are just another form of heat pump with a COP greater than one. While Wikipedia (cited above) assures me that they have a COP greater than 1.0, I have yet to find a source that will pin that down further. The best I’ve found is a passing reference to a COP of around 1.0 for a deep freeze unit (per this reference).
The bottom line is that a typical home freezer might use somewhat less than 0.063 KWH to remove 0.063 KWH of heat energy from its interior. But how much less, I can’t find the source that will let me pin that down. I suspect that, given the large temperature differential between interior and exterior, the COP of most freezers isn’t much higher than 1.0 or so.
Finally, KWH is not the same as GHG (greenhouse gases). This only measures energy consumed within the home, and does not differentiate between natural gas and electricity. Fossil-fuel based electrical generation is far from 100% efficient, so the actual amount of fuel consumed (to generate the electricity) is a low multiple of the energy actually delivered to the house. But in addition, electrical generation consists of a mix of generation sources, some of which create greenhouse gases, some of which do not. If the ultimate question is one of carbon footprint, we’d have to modify this calculation, treat electricity and natural gas separately, and then redo it for some assumed electrical generation mix.
That said, when I take a rough cut at the difference between natural gas (burned in a stove) and electricity (produced with a typical U.S. generating mix), I’m not sure that adjusting for each fuel type separately would make much difference.
Natural gas releases 100% of its energy within the home. But a typical natural gas stove is only about 40% efficient. That’s the energy that goes into whatever you are trying to cook, with the rest simply serving to heat up the kitchen. Basically, for every 100 units of C02 produced, you get 40 units of usable energy from your gas stove (Whatever units might mean, in this case).
For electricity, by contrast, the amount of fuel burned at the generating plant is far more than the amount that makes it into your home. But once it gets to your home, I’ve either directly measured 100% of what was consumed, or the theoretical calculation (for freezing) should be close to that. And so, as with natural gas, for every 100 units of C02 produced in generating electricity, you get X units of usable energy in the home.
The problem is that X depends on the generating mix that feeds your particular section of the grid. Even so, let me do the arithmetic for Virginia’s electrical grid.
Last time I checked, Virginia’s electrical grid released 0.7 pounds of CO2 per KWH of electricity delivered. Starting from that, I’m going to compare C02/KWH of usable energy for the Virginia grid versus a 40 percent efficient gas stove.
The EPA shows that burning a therm of natural gas releases an average of 0.0053 metric tons of C02. At 2204 pounds per metric ton, that’s 11.7 pounds of C02 per therm. A therm is 100,000 BTUs, and there are 3.4 BTUs per watt-hour.
Slapping that all together, burning a therm of natural gas produces 11.7 pounds of C02 and 29.4 KWH of (heat) energy, or 0.4 lbs C02 per KWH.
But a natural gas stove is only 40% efficient. A stove has to use (1/.40 =) 2.5x as much natural gas to deliver that usable KWH of heat. The bottom line is that a 40 percent efficient natural gas stove releases 1.0 pounds C02 for every usable KWH of heat delivered in the home.
And so, per KWH of usable energy, in terms of GHG emissions, electricity (in Virginia, at 0.7 lbs C02 per usable KWH) is slightly cleaner than natural gas burned in a (typical) 40 percent efficient stove. But only slightly. So the electrical options actually perform a little bit better than shown in the table above, relative to the gas-stove-intensive canning.
There’s nothing in any of that to change the conclusion that tossing your tomatoes into a freezer that would be running in any case is by far the most energy-efficient way to preserve them.
So, what about that vacuum sealer?
All of the above brings me back to my new toy, the vacuum sealer. If I’m going to freeze my tomatoes, the binding constraint is now the space they take up in the freezer, and secondarily, the length of time they’ll last once frozen. Both of which will be best addressed by vacuum-sealing them.
Most sources suggest that you freeze the tomatoes before vacuum-sealing. But at least one source shows tomato chunks that were vacuum-sealed and then frozen. That’s what I’m now aiming to do, only using whole tomatoes, not chunks. Given the literal tons of force that one of these sealers can generate, I’ll have to use the setting that allows the strength of the vacuum to be controlled manually. In the end, I’m aiming for a freezer stocked with nice, flat, well-preserved packages of energy-efficient frozen tomatoes.
With any luck, we’ll see how that all plays out in a few months.
In my last experiment, I showed how well a Ball (mason) jar worked as frost protection. In the coldest part of the night, the inside of the jar stayed 10 degrees F warmer than the outside. I thought that was exceptional performance for a lightweight uninsulated glass container. My explanation is that the glass traps long-wave infrared. And so, this works for the same reason that my radiant-barrier frost protection works. It prevents the garden bed from radiating heat energy off into space.
Long-wave infrared absorption would explain why glass worked well but polyethylene sheet was a near-total failure. A sheet of ordinary window glass will absorb about 86% of long-wave infrared, and reflect the rest. Polyethylene, by contrast, was reported to be almost completely transparent to infrared.
Accordingly, where a glass jar works well as a garden cloche, I figured that a plastic jar would not. And that’s what I tested last night.
Never let facts get in the way of a good argument.
There’s just one problem: Different plastics have different infrared absorption spectra. And it took me a while to track that down.
Using Wein’s Law, the spectrum of radiation emitted by my 50 F garden subsoil would peak somewhere around:
10 microns (micrometers) wavelength
10,000 nanometers wavelength
1000 waves per centimeter.
Those are three ways of saying the exact same thing.
So I wanted to find out how different plastics behaved with respect to long-wave radiation somewhere in that vicinity. That’s where most of the power from the upwelling long-wave radiation from the garden bed will be concentrated.
I never did find exactly the data that I wanted. But I came close. And, as it turns out, polyethylene’s absolute transparency in that region of the spectrum is the exception among plastics, not the rule.
The chart below show the absorbance spectra of various common plastics, with the long-wave infrared region highlighted. Note that the line for polyethylene is almost completely flat in that region. It absorbs almost no long-wave infrared. But PETE plastic, just below that, in fact absorbs infrared strongly right at the frequency where infrared from the soil will have its peak — wave number of 1000.
The upshot is that when I condemned all plastic for this use, I was too hasty. Avoid polyethylene, for sure. But, assuming the glass choche works as I have described it, PETE plastic ought to work reasonably well. Not as well as glass, but certainly not as poorly as polyethylene.
As an odd little footnote, Mylar plastic — the kind used to make space blankets — is the same stuff as PET/PETE plastic — polyethylene terephthalate.
Results
Below is a photo of a quart Ball jar (right) and the thick-walled PETE jar that I’m going to test. That was as close as I could get to the same size and shape as the Ball jar. FWIW, the PETE jar originally held salad dressing. You can see that it’s much thicker than (e.g.) a typical disposable water bottle or soda bottle.
When I tested that last night — two temperature loggers on a raised garden bed, one covered with the PETE bottle, one un-covered — sure enough, PETE works pretty well. But not as well as glass.
At the very coldest part of the night, the PETE jar provided between 4 and 6 degrees F of protection, or about half the maximum protection observed for the glass jar.
The lesson here is that when I condemned all plastics for use in frost protection, I was too hasty. Polyethylene sheet is a terrible choice, from the standpoint of trapping long-wave infrared. But PETE’s OK. Not quite as good as glass, but pretty close.
As the Town of Vienna rethinks the economic and human impact of its centralized leaf collection, maybe this is an opportunity to rethink the environmental impact as well.
In this post, I suggest something the Town of Vienna might do to reduce the environmental harm of centralized collection and disposal of leaves.
Briefly: Give equal footing to policies of “put your leaves out for collection” and “better yet, don’t do that”. That is, raise awareness that the most environmentally sound way to dispose of leaves is to let them decompose in your yard. At the same time, make sure that citizens are aware of the substantial harm that centralized leaf collection and disposal does to our local population of butterflies and other pollinators. Maybe offer little “rustic butterflies” to match the “rustic hearts” that are all over town, signifying a household that promises not to rake their leaves to the curb every fall. Continue reading Post #1463: The Town of Vienna and leaf collection: What if we put the environment first?
I’ve just been taught a first-hand lesson in why hardware stores sell 30% acetic acid (vinegar) as weed killer. That’s because regular household-strength (5%) may or may not work.
