Preventing Sulfur Off-Odors In Cider
Last updated: 2/2022
Applies to: cider producers looking for techniques to prevent the formation of sulfur off-odors (mainly hydrogen sulfide) before and during fermentation.
Why Does This Cider Stink?
Cider has a strong propensity to develop sulfur off-odors which are largely attributable to hydrogen sulfide (H2S). There are several variables and potential sources of these off-odors. This guide has been created to determine critical control points for preventing sulfur off-odors before they develop.
Terms used to describe sulfur off-odors include:
- H2S (Hydrogen Sulfide)
- Rotten Egg
- Burnt Rubber
How are these odors created?
- Elemental sulfur from orchards or storage
- Sulfur dioxide (sulfite) additions to prevent spoilage or oxidation in juice
- Sulfur from sulfur-containing amino acids
- Naturally occurring sulfates in apples
These can all be utilized during yeast metabolism to produce sulfur-containing compounds required for cell growth and function (including amino acids like cysteine and methionine). Sulfites from SO2 additions and elemental sulfur from orchards/storage can also bypass this process and be immediately reduced to hydrogen sulfide1.
If yeast become stressed for nitrogen, there are two path-ways that may generate H2S. First, in the presence of low nitrogen, the pathway that incorporates nitrogen and sulfur into sulfur-containing amino acids (cysteine and methionine) is blocked. The excess S-2 is converted to hydrogen sulfide2. Second, in the presence of low nitrogen, yeast will degrade their own amino acids for nitrogen. When those amino acids also contain sulfur, H2S is released as a by product1. Yeast strains vary in the potential amounts of H2S they will produce in this process.
Preventing Sulfur Off Odors During Fermentation
Fermentation is the stage at which many sulfur off-odors develop. The keys to preventing sulfur off-odors during fermentation compensating appropriately for the juice’s nutritional shortcomings and maintaining a low-stress environment for yeast.
Compensate appropriately for the juice’s nutritional shortcomings
Even in freshly harvested “high YAN” juices, significant supplementation may be necessary. If not working with fresh juice, even more supplementation may be necessary. The method of acquiring apple juice for cider fermentation will have a strong influence over the nutrient content. This can be attributed to two main factors:
- Length of storage: longer storage times (of juice and apples) allow native microflora to consume YAN, leaving juices deficient.
- Degree of clarification: juices that are too turbid are linked to H2S production. Conversely, juices that are too clarified can cause yeast stress as yeast will struggle to stay in suspension. It is recommended to clarify to 50-80 NTU or 1-2% solids.
Fresh Juice may have sufficient YAN if freshly harvested and pressed, or may have low YAN if the apples have been stored prior to pressing. Either way, fresh juice will be very turbid and require some clarification.
Bulk Juice/Stored Juice may be YAN deficient depending on the length of storage. These juices may have also been clarified or may have had a lengthy amount of time to settle, so they may struggle with over-clarification.
Concentrate typically has more YAN than the freshly pressed juice from which it was made3. However, the YAN in the reconstituted juice will heavily depend on the degree of dilution. Additionally, concentrate is intensely clarified during production since it receives multiple enzyme treatments, and over-clarification may be a concern.
As discussed on page 23 of the Cidermaking Handbook, yeast nutrition is more than YAN. The form of nitrogen added (amino acids vs. ammonia) is important. Yeast will also need vitamins, minerals, and sterols. See pages 24 and 30 for information on proper nutrient timing and dosages.
Maintain a low-stress environment for yeast during fermentation
Certain choices can be made during fermentation that can pre-emptively prevent H2S production:
Yeast Selection and Handling
The best practice is to inoculate with a commercial yeast strain. Commercial strains are incredibly reliable when rehydrated appropriately, inoculated at the recommended rate, and their temperature tolerances are respected. These strains have been specifically isolated and tested to withstand fermentation conditions of specified alcohol levels and temperatures without becoming stressed. Furthermore, certain yeasts are verified to be low to no H2S producers (BE FRUITS™, ICV OKAY™, ICV OPALE 2.0™, SENSY™).
We recommend avoiding indigenous fermentations. Indigenous yeasts are often less tolerant of fermentation conditions, may become stressed easily, may struggle to finish fermentation, and may produce a host of undesirable compounds like ethyl acetate. Re-pitching or yeast harvesting can be problematic as well since these yeasts have exhausted enzyme systems and/or contain microbial contaminants.
Avoid Other Environmental Stress
Yeast stress can also be induced during fermentation by high oxygen, low pH, and extreme temperature. Juices with high dissolved oxygen consume YAN more quickly and leave the juice depleted before the end of fermentation, causing yeast stress. pH during fermentation can drop during the first 18-36 hours, and a drop below 3.0 can induce yeast stress. Fermenting at the upper or lower extremes of a yeast’s temperature range will also induce yeast stress.
This article is featured on page 41 of our 2022-2023 Cidermaking Handbook. Download the complete book below.DOWNLOAD PDF
- Zoecklein, B. (2008, February). Managing Sulfur-like Off Odors in Wine. Wine Business Monthly.
- Iland, P., Bruer, D., Bruer, N., Caloghiris, S., Edwards, G., Ewart, A., Ford, C., Markides, A., Sitters, J., & Wilkes, E. (2021). Techniques and methods for chemical, physical and sensory analyses and tests of grapes and wine. Patrick Iland Wine Promotions Pty Ltd.
- Rosend, J., Kaleda, A., Kuldjärv, R., Arju, G., & Nisamedtinov, I. (2020). The effect of apple juice concentration on cider fermentation and properties of the final product. Foods, 9(10), 1401. https://doi.org/10.3390/foods9101401
Last Updated: 2/2022