A Matter of Color – Why does Zesterra darken with age?

At least a few times a week we get this inquiry — why did my Zesterra® darken since I bought it? This is a perfectly valid question — after all, in most cases, when the color of food or even things like toiletries shifts, it can be a sign of spoilage.

So, does a deeper shade of amber in Zesterra® herald its imminent demise? Luckily, no.

The reason behind that color change comes down to plain chemistry. Because we don’t use preservatives, the all-natural apple flavoring starts to go through a process known as oxidation. Just like when you cut open an apple and it immediately starts to take on a brown hue, so too does the apple flavor in Zesterra®.

But how? Apples contain an enzyme called polyphenol oxidase (also known as PPO), which, when released by damage to the tissue and consequent oxygen exposure, oxidize the polyphenols.

The other part to these inquiries usually involves shelf life. Zesterra has a 5-year shelf life and is incredibly stable — most of us keep a bottle in our trucks or trailers, our tack rooms and in our houses. If it freezes overnight because you forgot it out on the porch, that shouldn’t be a problem. Nor should leaving it in the hot truck for a few days.

Obviously, as with anything, we suggest you exercise common sense. If your Zesterra smells “off” or has become particularly thick or gloppy, it may be time to retire it. These problems are usually associated with contamination so it really shouldn’t be used anyway.

While this is just a quick overview, as always, please don’t ever hesitate to contact us with questions. We pride ourselves on being able to offer you solid answers based on facts and our own personal experiences with our products.

© 2019 Pro Earth Animal Health.

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