What exactly are phenolics? Are they tannins? I don’t think there a simple answer. If I told you there are two basics compounds, flavonoid and non-flavonoid types of phenolics, would that clarify it? It didn’t for me but, chemistry wasn’t my favorite subject in school. If I broke down the flavonoids into anthocyanins, flavan-3-ols, and flavonols and non-flavonoids into hydroxybenzoic acids, hydroxycinnamic acids, and stilbenes, is it all clear now? Yes, I felt the same way. That’s partly why I set out to write this article. I needed to better understand this complex yet very important aspect of hard cider. It is what I believe most people name tannin versus phenolic compound. We use the word tannin to describe a compound that imparts bitterness and/or astringency when eaten or drank. But phenolic compounds are more than just tannins and they contribute much more than just some bitterness and astringency. They impact organoleptic characteristics, which include color, clarity, aroma, and mouthfeel. They can also provide positive health benefits given their anti-oxidant and anti-inflammation abilities.
Part of the mystery of phenolic compounds for me is that they aren’t easy to identify and measure. You can look at oxidative browning as an indicator but that would just be part of the total phenolic levels found in an apple or juice. The apple variety as well as the orchard, maceration, and fermenation practices all impact the amount of phenolics you can have in your apple, juice, and ultimately cider. Apple variety is probably the biggest influence regarding what phenolic compounds are present, where they are present, and how much is present. However, the processes used to make cider can have a significant impact as well. Here are some examples of how processes can impact these compounds.
- Fruit Ripeness: Unripe fruit is higher in phenolic compounds than ripe fruit but overripe fruit is also usually even higher. However, using unripe fruit can contribute to haze and have low sugar while overripe fruit can have low yield.
- Maceration: Macerating your fruit after milling or grinding your apples will increase the level of phenolic compounds in the juice. Macerating at higher temperatures and including pectic enzymes will increase it even more.
- Fermentation: Including peels in your fermenter will increase the phenolic compounds in your cider as the peel and the seeds have the highest levels of these compounds in the apple.
- Oxidation: Exposure to oxygen during any phase of the hard cider making process can reduce the level of phenolic compounds in your cider. Many phenolics like to bind with oxygen. It’s what makes many of them beneficial to human health as they are great anti-oxidants.
These are just some examples of how processes can impact phenolics but even these are complex when you look at specific actions. For example, not every kind of phenolic compound is increased during maceration. In some situations, you might increase the anthocyanins but decrease other flavonoids. The total net phenolic compounds will generally be higher. Some reductions occur while other compounds increase. It’s why most research papers I read end with a comment like additional research is needed in this area. Micah Martin in their graduate thesis paper on phenolic compounds(1) presented a wonderful chart breaking down the common phenolic compounds found in apples. It’s one of the first times I have seen these compounds broken down in a way that helps bring some understanding to all these various compounds. Let’s explore the main three types: Phenolic Acids, Flavonoids, and Polyphenolics found in apples.
Phenolic Acids
There are several phenolic acids in apples with hydroxycinnamic acids like caffeic acid and ferulic acid being common. Chlorogenic acid is derived from caffeic and quinic acids. It is one of the more common phenolic acids found in apples. Its highest concentration is generally in the core around the seeds. It is an aromatic ester. It is also known to have antioxidant, free radical-scavenging, antibacterial, and antidiabetic properties, as well as neuroprotective activity(2). As you can see, there are numerous types of phenolic acids and the various derivatives that are produced from them.
Flavonoids
Flavonoids are the second type of phenolic compound commonly found in apples. One of the main compounds is anthocyanins, which contribute color and astringency to cider. They are odorless so they aren’t creating volatile compounds. The peel has large amounts of anthocyanins. Flavan-3-ols are another common flavonoid. These include catechin and epicatechin which are present in the flesh, peel, and core area around the seed. They are also astringent and not bitter. Another common flavonoid is rutin, which is a flavonol commonly found in the flesh and peel. The peel generally has larger amounts. It is derived from quercetin and contributes bitternessand health benefits. These are just a few of the common flavonoids found in apples, which can impact color, bitterness, astringency, and aroma.
Polyphenolics
The most common polyphenolics found in apples are proanthocyanidins. These are chains of flavonoids linked together, especially catechins and epicatechins. They are also the compounds we often call tannins though you might now see how that term is really too generic. They are polymers and also called condensed tannins. Polymers are simply large groups of the same molecules chained together. The condensed term is another reference to these long chains. Instead of having independent catechin or anthocyanin molecules in your hard cider, you have a mass of them chained together creating polyphenolics. Breaking down these polyphenolics will yield the individual modules. These compounds are a key part of plants defenses against predators and disease. They offer anti-inflammatory, anti-oxidative, and other beneficial health properties. They can impact taste and provide astringency and bitterness. They also impact color and aroma.
I admit that phenolic compounds are still a little mind boggling to me. Part of this is because there are so many of them and they impact so many organoleptic aspects of your cider. I find it easy to get confused and can understand why just calling everything tannins could be easier. If you are like me, don’t worry. From the numerous research papers I have read, that confusion isn’t ours alone. The research into this area is just starting to be understood but as I noted before, most papers include the statement that more work is needed in this area. However, I hope this article helps us to start talking about anthocyanins or catechins and polyphenolics and not just tannins.
(1) M.A. Martin, Addition of endogenous tannins for improving the quality of fermented cider and the development of a pomace-derived tannin concentrate, Thesis for Graduate Degree, August 2017
(2) C.M. Castillo-Fraire and associates, NMR structural elucidation of dehydrodimers resulting from oxidation of 5-O-caffeoylquinic acid in an apple juice model solution, Food Chemistry 372, 2022
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Good article. I have been trying to figure this phenolics for a long time and have been similarly confused. That chart was very helpful. Thanks.
I have noticed that bitterness and astringency go down as an apple ripeness but I have not seen it go up as it becomes overripe. Can you do a follow up article on that (ie, which phenolics are going down, which are increasing)?
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I’ve read several papers on fruit ripeness and phenolics compounds. The best is A. Alberti and associates, Impact on chemical profile in apple juice and cider made from unripe, ripe and senescent dessert varieties, Food Science and Technology, 65, 2016.
I touch on this in my post about apple ripeness. As always, the up-down-up cycle of phenolics does depend on the variety. For example, Fuji Suprema didn’t follow this cycle while Gala and Lis Gala did. That was similar results to other papers. For Gala, Hydroxycinnamic acids, Flavonoids, Flavanols, and Flavonols all increases going from ripe to senescent while Dihydrochalcones went down. Lis Gala went up for Hydroxycinnamic acids, Flavonoids, and Flavanols but down for Flavonols and Dihydrochalcones. For Fuji Suprema, only the Flavonols went up. In another paper, Antei, Kulikobvskoye, Melba, and Orlovski Sinai apples all went up in the Dihydrochalcones going from ripe to overripe. Other compounds like Hydroxycinnamic acids, Flavonoids, Flavanols, and Flavonols were mixed depending on the variety. This was a study by O. Laaksonen and associates called the Impact of apple cultivar, ripening stage, fermentation type and yeast strain on phenolic composition of apple ciders. I’ll keep researching and writing about phenolics as I get a better understanding with new paper I find. Thanks for reading and the questions!
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