Ask Pablo: Which Favorite Holiday Pie Is The Greenest to Bake?

Dear Pablo: With the holidays approaching, I am wondering which pie is the greenest -- pumpkin, apple, or pecan?

For many of us pie is one of the best things about the holidays. With so many pies to choose from, why not figure out which one will have the lowest impact on the environment? Will is be the silky pumpkin pie; the old American standard, apple pie; or the delicious pecan pie? I just hope it's my favorite!

Life cycle assessment is a tool for assessing the environmental impact of things or actions. It can be applied either in absolute terms, like determining the "carbon footprint" of a bottle of wine; or in relative terms, like deciding which pie has a lower environmental impact. In this case the carbon footprint of a pie would provide little value unless you were buying greenhouse gas offset credits to counteract your pie's impact. Instead, we want to understand the relative impact; we want to know which of the three pies has the lowest environmental impact.

What Is The Impact Of Pie Ingredients

Other than their namesake ingredients, our pies are more or less made with the same ingredients, flour, sugar, eggs, and butter. Flour is made from wheat that is irrigated and cultivated with large machinery, and sugar is made from sugarcane, whose waste is burned in the fields. Eggs are produced in sometimes inhumane conditions, and butter is made from cows that may be given growth hormones or unnecessary antibiotics and are responsible for up to 50% of the earth's methane emissions.

Yet none of this matters when comparing our three pies, because these variables will be more or less the same, regardless of the pie. For you nit-picky bakers out there, let's just assume that the apple pie has no lattice on top so that all pies use the same amount of dough.

What Is The Impact Of Your Trip To The Store?

Believe it or not, the largest contribution to greenhouse gas emissions from most of your purchases is from your trip to the store. This is especially true if you make the trip for only a single item. May this serve as a reminder to borrow that stick of butter from a neighbor before jumping in the car.

It may seem counter-intuitive that those giant trucks on the highway are more efficient but they carry a much larger load. A truck can carry a kilogram of product over 100 miles with little more than 30 grams of greenhouse gas emissions while the same trip in your car might emit up to 50 kilograms. That's 1667 times more! But it begins to make sense when you think about that 2,000 pounds of steel are being driven around town to transport a single gallon of organic 2% milk.

The point here is that your trip to the store matters, but in comparing our three pies it doesn't matter because you have to go to the store no matter which pie you choose (assuming that you don't have any of the ingredients already).

What Is The Impact Of Baking Pie?

In your kitchen you may be softening your butter in the microwave, blending ingredients in a food processor, and you are definitely baking your pie in an oven. All of these appliances use energy and created a little bit of environmental damage as a result of their manufacturing. Of course, none of this matters for our comparison because you will be using your appliance regardless of the pie that you choose.

What Is The Impact Of The Main Pie Ingredient?

Finally we have arrived at the crux! The main differentiator between the three pies is, of course, their namesake ingredient; pumpkins, apples, and pecans. For this part I will turn to one of my favorite sources on environmental impacts and energy use in agricultural, the UC Davis Cost and Return Studies.

What Is The Impact Of Pumpkins?

An average yield for a pumpkin patch is around 15,000 pounds per acre. To achieve this yield the farmer must use:
    205 gallons of diesel for far equipment,
  • 800 pounds of blood meal,
  • 5 tons of compost,
  • 667 pounds of phosphate,
  • 400 pounds of oyster shell lime,
  • 50 pounds of potassium sulfate,
  • 7,200 feet of 6' wide plastic sheeting,
  • 2 pints of Neemix insecticide, and
  • 5.25 acre-feet of water (~1,700,000 gallons).

What Is The Impact Of Apples?

An Apple orchard yields about 9 tons per acre, 2.7 tons of premium apples, 4.5 tons of standard apples, and 1.8 of "utility" apples. The farmer uses:
  • 16 gallons of gasoline,
  • 87 gallons of diesel,
  • 10 pounds of boron,
  • 21 pounds of calcium nitrate,
  • 3 acre-feet of water (~1,000,000 gallons), and
  • almost 10 gallons of various herbicide, fungicides, and pesticides.

What Is The Impact Of Pecans

Pecans yield 1,700 pounds per acre. The farmer will use:
  • 9 gallons of gasoline,
  • 20 gallons of diesel,
  • several pints of herbicide and acaracide,
  • 150 pounds of nitrogen fertilizer,
  • 24 pounds of urea,
  • 48 pounds of zinc sulfate, and
  • 4.67 acre-feet of water (~1,500,000 gallons).

Which Pie Is It Going To Be?

At first glance it may appear that the pecans have the lowest environmental impact, the least amount of fuel use, low fertilizer use and low biocide use as well. If we were looking at the impact per acre this might be a correct conclusion but pecans yield relatively little per acre and therefore the impact per unit of pecans is much higher.

Comparing pumpkins and apples is a little tougher. While Apples use more biocides, they yield slightly more and use less water, fertilizer, and fuel. And here we see one of the problems of a "apples to oranges" comparison. Unless we know the exact biocides being used on the apples and their relative impacts, we can't conclusively say that apples are better, but all other indicators point towards a win for that old American standard, and my personal favorite, the apple pie.

There are a few more things to consider. An apple pie weighs about twice as much and a slice is typically bigger. Since pumpkin and pecan pies are sweeter, the servings aren't as big. In life cycle assessment you look at the impact of a product per "functional unit." So far, we have looked at the three ingredients based on a common unit of mass. We can also look at the functional unit as one slice. Since the apple pie slice is likely to be bigger, its greenhouse gas emissions per slice are going to be roughly the same as its two competitors. We could also look at the functional unit as 100 calories of pie. If you want to do that, go right ahead, but I think that would be too depressing.

Still wondering what the carbon footprint of a pie is? Well, a true life cycle assessment would take weeks to perform properly but, relying on my professional experience, I would guess between 5 and 12 pounds of greenhouse gas emissions per pie.

Ask Pablo: Which Favorite Holiday Pie Is The Greenest to Bake?
Which holiday pie is greenest? Pumpkin, apple, or pecan? Find out in this week's Ask Pablo!

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