September 01, 2021

Exploring Diversity of Cider Profiles Through the Selection of New Yeast Strains

This article is an extract of a technical article written by the Fermentis team, click here to discover the full article and data.

Introduction

Although the global cider market has been constantly growing over the past 15 years, the growth rate has progressively slowed down in the last 5 years. We see from the last data published (AICV) that the significant increase of consumption observed between 2005 and 2015, from 13.5 million hectoliters (MhL) to 24 MhLs, -- mainly driven by new regions such as here in North America, Australasia, and Africa versus older markets such as West Europe and Latin America --progressively flattened out to reach about 26 MhLs in 2019. 

In this context, cidermakers are facing competitive challenges and need to find new ways to boost their market by standing apart from each other. Among the main diversification tools are the choice of the raw materials and the recipe; but also the selection of the yeast strain. The conditions applied to carry out the fermentation can drastically affect cider organoleptic profiles. In this way, Fermentis team selected four new yeast strains to help cidermakers in this creative endeavor.

Criteria for Yeast Selection

Have you said Cider?

What could be considered as a “cider” is actually very variable depending on the countries and the substrates: 100% apples, types of apples, addition of other fruits such as pears, usage of juice, concentrates, and external sugars. Because the of the variety of recipes and mix of ingredients, a standard study is almost impossible.

Fermentis analysis was based on 4 major recipes that could embrace the main problems faced by cidermakers around the world: types of apples used, source and quantity of sugars, completion or voluntary stop of fermentation (to eventually leave some residual sugars), and fermentation temperature. Main cider styles studied included:

  • Traditional French Sweet Cider
  • Traditional English Dry Cider
  • French Dry Cider for distillation
  • American Dry Hard Cider

Fermentis Cider Yeast Trials

All fermentations have been carried out at the experimental cellar of the Institut Français des Productions Cidricoles (IFPC), French research institute specialized in cidermaking; in 15L glass vessels, with a standardized oxygen rate addition (1.5mg/L) and under inert atmosphere (N2).

Strain characterization

From the traditional French sweet cider to the American hard dry cider, the fermentation conditions became increasingly difficult even though nutrition and temperature were adjusted. It was interesting to try different yeast strains through all these recipes in order to select the most diverse and interesting ones. From more than 20 strains evaluated at the beginning of the process, Fermentis has specifically selected four of them:

You’ll find here below some information to help you to pick the right yeast for your next cider.

Let’s talk first about robustness of the strains. Some conditions are more stressful than other for yeast strains and these conditions depend of the cider you want to produce, i.e. high sugar concentration (and content in the most difficult to assimilate fermentable sugars, i.e. fructose), low pH, nutrient deficiency, low temperature. Fermentis has clearly identified that the strain SafCider™ TF-6 stands apart from the other strains as it was not able to finish the fermentation and typically left ~25 g/L of sugars, among which fructose was a major part. This feature was observed in most of all matrices meaning that, generally speaking, this strain is more adapted when you’re looking for a sweet cider with roundness in mouth.

Analytical profile

All basic analytical parameters at the end of the fermentation have been determined by the Fermentis team. Among the most interesting ones, the acidity profile is of particular interest as it reflects the metabolic behavior of the strain that could have a real impact on the organoleptic profile.

Most significant with SafCider™ AB-1 and maybe not as much with the other strains, we could see that some strains are able to consume the major organic acid present in apples, i.e. the malic acid, in significant amount through the malo-ethanolic pathway; and thus decreasing the total acidity and its feeling.

To the  contrary, some strains, such as SafCider™ AC-4, are preserving this acidity and maintain a crispy feeling. Moreover, the ability of strains to produce acetic acid during fermentation from the glycolysis pathway can also affect the aromatic profile, degrading its quality at too high concentration (vinegar flavors). For this attribute, all strains were selected for their low production with always the SafCider™ TF-6 being a “clean” strain towards deviations like SO2 and acetaldehyde production as well.

Fermentis Chart

Aromatic profile

In addition to higher alcohols, two major types of aromatic compounds are produced by yeast strains during fermentation and have a significant impact on the aromatic profile of all beverages:

  1.  the acetate esters, whose most famous and abundant one is the isoamyl acetate with its distinctive banana and candy notes and which is recognized as an overall aroma enhancer; and
  2. the ethyl esters, whose most abundant ones are the linear chain ethyl esters from 4 to 10 carbons (C4-butanoate, C6-hexanoate, C8-octanoate and C10-decanoate) and which confer more discrete but more complex floral and fruity characters. Huge differences in the release of these compounds can drastically affect the flavor perceptions of beverages, the same applying for ciders.

The production of these compounds is really variable depending the recipe and the yeast strain used allowing to cidermaker to adjust the aromatic profile they are looking for.

  • Except for the English cider, SafCider™ TF-6 showed higher production of isoamyl acetate than others. This will impact flavor but also aromatic intensity.
  • SafCider™ AC-4 showed particularly high but quite stable ethyl esters production (driven by ethyl octanoate – fruity/floral), hypothesizing a reliable complexity in the flavors.
  • SafCider™ AB-1 and particularly SafCider™ AS-2 increased their ester production along with the “difficulty” (dryness is more difficult to reach for the yeast than sweetness) of the recipe with SafCider™ AB-1 being on the low values, more respecting the raw material.

Sensory Analysis on French Sweet Cider

Relying on the expertise of IFPC and their trained taste panel specializing in French traditional sweet ciders, professional tastings have been carried out on French cider experiments, both stopped with around ~30 g/L of residual sugars (called “Brut” ciders in French). The specificity of this tasting was to assess first the global fruitiness of the ciders with two major descriptors:

  1. "Fruity/Floral” corresponding to fresh fruit (apple, pear, banana…) feeling; and
  2. “Cooked fruits” related to ripe or processed fruits (like compote), aromas that are not necessarily looked for but adding complexity to the final cider.

After this evaluation, tasters were asked to detail fresh and cooked fruit notes to identify the aromatic drivers for each strain and to evaluate off-flavors as well, such as phenolic and sulfur aromas. Finally, a simple evaluation of the basic tastes was done: sweet, acid, bitter and astringent.

From these tastings, SafCider™ TF-6 (especially) and SafCider™ AS-2 were scored as the highest in fresh but also cooked fruits, whereas SafCider™ AC-4 was judged less expressive and predominantly oriented towards freshness; and SafCider™ AB-1 was more discrete.

Obviously, sensory characterization of all ciders was driven by detection of apple notes, but SafCider™ TF-6 scored high for most of the fruits, especially banana-pear and red fruits. SafCider™ AS-2 and SafCider™ AC-4 respectively exhibited more citrus and floral notes, whereas SafCider™ AB-1 was mainly centered on apple.

Conclusion

Yeast strains have a huge impact on cider profiles, not only in terms of fermentation performances and analytics, but also from a sensory perception. Cidermakers can experiment with them to achieve their final product target. Fermentis focused its research on the selection of valuable strains dedicated for ciders.