apple pie

Apple pie – It’s all about the apple (science)!

There are tons and tons of recipes for apple pie (such as our Dutch one). They use different crusts, different ingredient ratios, maybe some additional add-ons. There’s so much to choose from.

However, most of these recipes fail to mention that the success (or failure) of your apple pie largely depends on one major thing: the apple you’re using! Is it tart, sweet or bland in flavour? Is it firm or soft, does it fall apart easily? The properties of your apples will, more than anything else, determine how your apple pie turns out (especially if you tend to fill you apple pie with loads of fruit).

So how do you choose your apples? It brings us into the world of apple growing, analysis and of course baking. Yes, we did an apple baking experiment to help you out (hence the strangely cut pie on the top of this post…). Hopefully this will all help you choose your apples wisely.

Apple varieties

Apples grow in quite moderate climates. They can withstand (and thrive with) temperatures below zero during winter, but can’t withstand long hot summers. The Netherlands is a great country for growing apples, but is small compared to the world’s largest producers, China, the US and Turkey. Within these countries certain regions make up for the majority of the apple production. Within the US that’s the northwest and northeast, within Turkey that’s roughly the south west.

As such, if you live in one of those apples producing regions, you may find anywhere from 1 to many apple varieties in your local stores. Within the Netherlands, apples are one of the few fruits of which there are many varieties in the supermarket. There might be two banana types (organic & conventional), two pear varieties and two oranges, alongside 8 different types of apples!

In a Caribbean country this is very different. Apples don’t grow well in these more tropical climates, instead you might find several varieties of mangos!

So why all those apple varieties? Naturally, apples, just like most fruits, have naturally evolved in a lot of different varieties. Unlike staple crops such as wheat, potatoes, etc. Most fruits weren’t primed for being just one variety. Instead, their smaller scale production and more temperamental behaviour kept more of that variety in place, resulting in over 700 different species.

apples
Just a few of the apple varieties out there

Different types of apple classifications

There are a lot of ways to group all these different apple varieties. To mention just a few:

  • Growing/harvest period: whether they ripen early into fall, or later in the year (most apples ripen in the fall on the Northern hemisphere).
  • Growing area: some apples prefer cold climes, whereas others prefer slightly warmer climates
  • Taste: sweet vs. sour
  • Colour: apples can be yellow, green, red and just about any colour in between
  • Usage: do you eat them fresh, or are they best put to use in a pie or sauce or even a cider?
  • Storage: whether you can keep them for long in storage, e.g. using controlled atmosphere which impacts the ‘breathing’ of apples

You will see these being used individually, but also in combination with one another (e.g. a sweet, late harvest long storage apple).

apple pie slice - bland harder apples
This apple variety did not turn soft. Instead, it kept its shape and still had a decent bite to it.

Analyzing apples

Most of the analysis of apples is actually done by the farmers (or researchers on farms), while the apples are still on the tree. These analyses focus on determining whether the apple is ripe enough for picking.

The types of analyses they’d commonly do are:

  • Colour: the colour of a fruit tells a farmer a lot about it’s ripeness, as apples ripen, they lose their green colour (chlorophyll), to what extent depends on the apple variety
  • Size: the size of the apple dpeends on growing conditions, but also has an impact on the structure and chemical composition of the apple
  • Firmness: it’s hard to measure firmness well and various tools exist out there, but it’s very important because it will drastically impact the eating (and generally baking) experience
  • Soluble solids content or Brix: measures for the amount of sugar (and some other components) in your apples
  • Dry matter content: this is the amount of material in an apple excluding the moisture content
  • Acidity: using the pH-value scale
  • Starch content: pretty simple tests using iodine exist for determining the starch content in apples. As apples ripen more starch is converted into sugars, so the amount remaining is a good indication for its ripeness.

Baking with apples

When discussing apple cider production, we discussed how to choose apples for your cider. So now that we know what types of apples there are and what you can analyze, what do you really need? How would you go ahead if you want to bake with your apples?

What happens when baking apple pie

A lot happens in the oven when you bake an apple pie. The crust of course cooks and sets, but let’s not look into that for now. Let’s focus on the apples.

During baking a pie the temperature of your apples increases considerably. The cells in an apple can’t withstand this heat. Instead, cell walls will soften and break down (as happens to kale leaves). The cells and their cell walls though are what make an apple firm and crisp (because of turgor), they keep the tension on the apple and the moisture inside. Once they break down the contents of these cells gets released and they loose this crispness. Hence the softening of the apples! Some varieties break down more than others when heated.

Because of these cells breaking down, and fluids being released some of the acidity may get lost as well (we see that for pears as well). All these molecules can float around and react with others so the flavour profile changes. Not only that, moisture evaporates. Unless you’ve completely covered your pie with dough, that moisture will leave the pie and making the apples slightly dried.In a lot of cases you actually want some of this drying to happen to prevent an overly soggy and wet filling!

slice of apple pie winesap
This apple variety (winesap) breaks down partiallyand softens while baking, slumping down creating a delicious center filling.

As is, unfortunately, often the case, the scientific literature on this topic is virtually non-existent. No research is available on the tartness or sweetness of apples and how it develops in the oven, how well they break down in the oven and how to measure this well. (If you know a student/researcher looking for a cool project, give them a hint and have them read this post! If you’re that researcher, reach out!).

Desired baking apple properties

So, we instead have to rely on cooking lore, generic tips and tricks. Trying to make it somewhat scientific, let’s look what we’re looking for in a good baking apple (we’re sticking with pie for now).

  1. Structure: the apples should turn soft in the oven, but you don’t want it to turn to mush! The strength of the internal structure is of importance here.
    Notice how pears are quite similar to apples in structure, but still make a very different texture?
  2. Flavour: the two main flavours tested for apples are sweetness (aka sugar content) and acidity (aka pH-value). If you’re baking an apple the quite intense heat treatment can result in a loss of flavour and tanginess because of a loss of cell structure. However, you want some of this freshness maintained. This is why generally quite sour apples are recommended for baking.

Testing apples

Since there is no one chart that will give you the sweetness, acidity and firmness of your apples for proper selection, you’ll have to go by the advice on which apples are best to use. This is a good initial strategy. However, if you’re planning to bake a lot of apple pies (let’s say you’re a professional baker) some more testing would be smart to do.

An easy way to test how an apple withstands the heat is to take a few slices of the apple, pack them in some aluminium foil (so they don’t dry out) and put them in a pre-heat oven (180C / 350F) for about 10-15 minutes. The structure they have turning out, is going to be like the one in your pie. It’s best to test a few apples per variety so you have some idea of consistency between apples (you could otherwise just happen to have selected an outlier).

Once you’ve selected your variety, write down why you chose it and do some additional tests with other varieties as you come across them. There might just be an even better one out there!

Choosing your apples

After all that theory it’s time to get back to our apple pie again. We prefer an apple pie with a strong apple flavour, a nice tartness and some acidity to it. It shouldn’t be bland, nor sweet. Generally, great apples we’ve used in the past are Jonagold, Goudreinet, Elstar and Winesap. We actually tested two of them (Jonagold & Winesap) in the apple pie below, along with a generic apple.

  • The generic apple had a bland flavour to start with. It didn’t taste that great just so, so we kind of hoped (foolishly) that baking it might cover up its weaknesses. Well, it did not, this way by far the most flavourless apple pie ever. Despite the extra lemon juice that we added to give it a boost it just wasn’t a good apple pie. What’s more, it didn’t break down at all in the oven. We didn’t want the apple to turn to mush, but this was the other extreme. Overall grade: 2 out of 10.
  • Jonagold is a good fresh, slightly acidic apple to start with, a pleasant eat. It also worked well in the apple pie. It was nice and fresh, had some zing to it and made a good apple pie. Overall grade: 8 out of 10.
  • Winesap: this is quite an acidic apple, if you enjoy somewhat acidic apples, this is yours, but for quite a few it might be a bit too much as is. However, in the apple pie it outperformed every other apple easily. It was fresh, vibrant, just soft enough, delicious. Overall grad: 10 out of 10.

We haven’t tested every single apple out there. Generally though, recommendations online would also advise using the following varieties for your apple pie: Rome beauty, Newton Pippin, Bramley, Prairie spy or a Honeycrisp. There are a lot more, and if you’re in doubt. Just test the apple out and you’ll know!

So, going forward, just use any apple pie recipe that looks decent and spend your time and effort to where it really matters: choosing the right apple!

apple pie
Wondering why the apple pie is cut in a somewhat peculiar way? We created three sections that each contain a different apple variety. Using the dough to mark the areas. We then cut one piece from each section to test!

Sources

Christine Brown, Amy, Understanding food: principles and preparation, 2014, p.306, link

Travers, Sylvia, Dry matter and fruit quality: manipulation in the field and evaluation with NOR spectroscopy, PhD thesis, 2013, link

Herrick, Christina, Why dry matter matters in apples, Nov-4 2014, Growing produce, link

Morroco, Chris, The best apples for baking, Bon Appetit, Sep-21, 2017, link

Quadram institute, Apple facts, link

University of Minnesota, All U of M apple varieties, link

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