Cider Words: Light Struck

The impact of light on cider.
The impact of light on cider.

Does light pose a risk to hard cider? Beer is bottled in amber bottles to prevent what is called light struck or skunky beer. This occurs when photosensitive iso-alpha acids form 3-methyl-2-butane-1-thiol (MBT). MBT has a skunk odor. If hard cider includes hops, it can form this fault as well when exposed to light. However, even traditional cider can be light-struck. The difference is that it has more impact on color and while aroma can be impacted, the odor fault is usually of boiled vegetables versus skunky. This is because for cider, like wine, one of the main compounds that are sensitive to light is riboflavin, also called vitamin B2. The fermentation process usually consumes most vitamins found in apple juice but some residual B vitamins can be found and B2 is one of those. Other compounds are also impacted by light exposure, including free SO2, phenolic compounds, and the Fe(III):Fe(II) ratio(1). The light accelerates the natural aging process found in wine. Another interesting aspect is that light is usually associated with heat, which also accelerates aging.

Amber bottles are the best way to minimize light struck conditions. They have been found to be more effective in reducing or delaying color and aroma changes when compared to green, blue, or clear bottles. However, the best solution is to avoid light. Kegs and the bag-in-a-box containers often found in England are great options that completely block light. Avoiding light is best because darker color containers, like amber bottles, absorb and retain more heat than clear containers. Avoiding sunlight which has UV light and heat is a good idea to reduce the potential negative influence that can be caused by photosensitivity and heat. The other component that is often needed to induce light struck conditions is oxygen. Most of these light struck reactions found in wine are oxidative. They need oxygen to occur. For wine, oxygen is often supplied through the cork or barrels used to store wine but it can also be added during processing or absorbed through plastic containers. This highlights another good reason to limit the exposure your cider has to oxygen.

So, traditional cider can suffer from being light struck but, the impact will often be a change in the color of the cider or some cooked vegetables aromas versus the skunk aroma found in beer.

(1) H. Lan and associates, Effects of light exposure on chemical and sensory properties of storing Meili Rose wine in colored bottles, Food Chemistry 345, 2021

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