Apple Appreciation 101
The overall flavor of an apple is dependent on the balance sweetness and sourness with a touch of bitter, the presence or absence of volatile aromatic compounds and some polyphenolic compounds contributing to astringent mouthfeels.
The most common sensory information that you will see regarding apples is their ratio of sweetness to sourness. All apples contain both of these basic tastes in varying degree. The best depiction that I’ve found of this is a visual called the Spectrum of Apple Flavors from the Sage Fruit Company, which places common apple varieties along a continuum from sweet to tart. For instance, most sweet/least tart are Fuji apples and most tart/least sweet and Granny Smith apples. Honeycrisp, my personal favorite is slightly more tart than sweet. It is also important to know that sweetness does not always correlate to the actual sugar content in the apple, which is usually measured by something called Brix (an interesting aside on Brix is that my local Wegmans grocery store sometimes markets their fruit by sharing the Brix levels). So, you can have an apple with a high sugar content (or high Brix) that is also very sour. And sour taste suppresses our perception of sweet taste. This is referred to as a basic taste interaction. Another example of a basic taste interaction is putting sugar in coffee to make it less bitter. The coffee still contains just as many bitter compounds, but we don’t perceive them as much since sweetness suppresses bitterness. So, to sum this up: when considering eating quality of apples, the relationship of sugars to total acids is often more informative than the sugar or acid contents separately.
The types of sugars in ripe apples are mainly sucrose, glucose, and fructose in the approximate ratio 1:1:2. Apples tasting of honey often have more than the usual amount of fructose. This is seen in Golden Delicious apples that are fresh and ripe. It should be noted that fructose, known as fruit sugar, is over 1.5 times sweeter than sucrose (the chemical name for white sugar). Some volatile aromatic compounds can also contribute to a honey flavor and may enhance perceived sweetness. We’ll talk more about these compounds in just a bit.
Now, the main acid found in apples is known as malic acid. Malic acid is also found in wine, rhubarb, and grapes. It is sometimes used as an added flavoring agent to impart a tart taste to foods. The name malic is based on “malum,” the Latin word for apple. Apples also contain acetic acid, also known as Vitamin C. This is why apples are a good source of vitamin C.
The other basic taste found in apples is bitter. We normally don’t think of apples as bitter, but they are slightly bitter. Bitter taste in apples comes from a wide range of polyphenolic compounds. Polyphenols are a class of health promoting plant based chemicals. Tannins, one type of polyphenols in apples, are also found in wine, especially red wine. Tannins provide bitterness as well as what is known as astringent mouthfeel, which is a drying or puckering sensation in the mouth. Bitterness and astringency may sound like a bad thing, but in small amounts they contribute to the tasty complexity of the apple eating experience. Bitterness and astringency is often strongest in or just below the skin. This may be why many people like to peel their apples. But remember, these bitter producing compounds are also extremely good for you!
Now, the most interesting nuances of an apple’s flavor comes from the volatile aromatics released when smelling and chewing. Classes of these compounds include: esters (fruity), alcohols (fruity or earthy), aldehydes (appley and slightly grassy), and ethers and terpenes (perfumey). There are over 200 distinct volatile aromatic compounds responsible for the subtlety of flavor within apples. For instance, the four most predominate compounds that contribute to the flavor of a gala apples are methylbutyl acetate, butyl acetate, hexyl acetate and butanol. The contributions of these singular chemicals as is relates to perceived flavor is not always straightforward but often an interplay of many.
Some of these compounds contribute to flavors such as honey, earthy, floral, spicy, pear-like, fennel, strawberry, raspberry, melon, blackcurrant, green grassy, grape, banana, and violets. Some of the flavors are characteristic of specific apple varieties. But unfortunately the level of reporting regarding specific flavors in apples is not well documented and most apple tasting guides will focus on sweet vs. tart and levels of crispness and juiciness. Some say that the Pink Lady variety has banana aromatics and the Cortland variety can by spicy and floral-like. And these various flavors can be fleeting based on the freshness and storage condition of the apples. My advice: take a bite, close your eyes and savor the flavor. What flavors do you perceive.? In fact, some experts suggest using a wine aroma wheel to provide guidance as to the wide array of flavors that can be perceived in apples.
The composition of volatile flavor components changes with maturation and ripening. When apples become overripe, flavors may be produced through enzymatic reactions forming free radicals. Off-odors and -flavors appear typically towards the end storage life and include acetaldehydes, ethanol and reaction products from fungal activity. Apples generally will start to take on moldy and fermented flavors while desirable flavors tend to go away.
When it comes to eating enjoyment, texture is equally important to flavor. There is almost nothing worse than biting into an apple that looks delicious and crispy on the outside only to get a big mouthful of grainy, tasteless, sawdust. This phenomenon is known as “mealiness”. Mealiness is when the “glue” holding the apple’s cells together gets weak. When this happens, a bite of apple will just disintegrate into individual cells when we chew instead of holding firmly together. To test for mealiness, try tapping the side of the apple: good ones will sound hollow while mealy ones will sound dense and dull. Mealiness happens when apples are old or improperly stored.
In addition to mealiness, experts evaluate apples on the following textural criteria:
- Hardness = the amount of force needed to bit into the apple. Hardness is also referred to as firmness. A good continuum for hardness would be McIntosh apples (very soft) to granny smith (very hard/firm). Generally speaking, harder/firmer apples hold up better in pies while softer apples are good for making applesauce.
- Crispy = hard but easily breakable; brittle, firm and fresh; not soft or wilted. Honeycrisp apples are probably the best example here.
- Juiciness = the amount of good tasting flavorful liquid in the mouth when chewing
- Sogginess = the amount of waterlike flavorless liquid in the mouth when chewing (I often find Red Delicious apples from my local gas station mini-mart to be soggy)
- Toughness of Peel = the amount of peel left in the mouth after 8 chew with molars
- Starchy = apples in which the carbohydrate has not fully converted to sugar. Try eating corn starch straight up to fully understand what the phenomena feels like in the mouth.
Some tasting tips:
- Refrigerate Your Apples—But Don’t Eat Them Cold: Some fruit, including apples, release a gas called ethylene when ripening. Sticking apples in your fridge halts this process. To keep apples crisp—and texture is a key factor for enjoyment—refrigerate them. Volatile aromatic compounds are easier to perceive at room temperature so leave them out for an hour or two before enjoying.
- Don’t Judge an Apple by Its Skin: You might not like the way an apple looks but you might like the taste. Also, certain colors of skin may sway your opinion on how it tastes. So a yellow apple could have a grape flavor and a red apple can have green grassy flavors.
- Fall is a great time to host an apples tasting party: Cut up several apples and blind code them so you don’t know the breed.