Bee Pollen as a Yeast Nutrient

As with grape wine, the fermentation and maturation process of mead can vary considerably due to multiple factors. Yeast has specific nutrient requirements for reproduction, with nitrogen (particularly yeast-assimilable nitrogen; YAN) being one of the most important. Other major factors that influence mead fermentation are low pH and low mineral content (lighter honey).

If these factors are not properly managed through the use of various supplements, the results could be a prolonged or stuck fermentation. For this post, I will focus on the efficacy of using bee pollen as a primary supplement of YAN, as well as other vitamins and minerals, required for a successful fermentation. Specifically, I will summarize some of the results of a research paper titled Influence of pollen addition on mead elaboration: Physicochemical and sensory characteristics.

Bee pollen is one of the several products that are collected from beehives. Honey and beeswax are by far the most popular, but bee pollen, royal jelly, and propolis also have many uses. Pollen is gathered as bees forage for nectar and is packed into balls (bee pollen) within the hive. This bee pollen is about 40% protein on average and serves as the primary protein source for bees. Bee pollen also proves to be an important supplement in improving the fermentation process of mead.

Here are some highlights from the study mentioned above:

Methods

Commercial honey (at 75 Brix) was diluted with water until a honey of 20-22 Brix was obtained. Acidity was corrected to 3.6. Potassium metabisulfite was added to prevent lactic acid bacterial growth. The diluted honey was divided into 5 L fermentation tanks and commercially produced pollen was added in concentrations of 10, 20, 30, 40 and 50g/L, for each treatment. A control with no pollen added was also included. After addition of pollen, turbidity and yeast-assimilable nitrogen (YAN) of the honey must was measured.

The honey musts were inoculated with a wine yeast strain of S. cerevisiae (ENSIS-LE5) at a dose of 15g/hL and incubated at 25C. Density and biomass were measured throughout fermentation. At the completion of fermentation, the meads were cold stabilized at 6C for one week, and then treated with gelatin (4g/hL) and bentonite (40g/hL). Lastly, meads were filtered and bottled. All treatments were performed in triplicate.

The following were measured for all mead treatments: nitrogen, amino acids, Beaumé degree, pH, total acidity, sulfurous anhydride, YAN, alcohol content, volatile acidity, residual sugars, and finally, major and minor aromatic compounds. To simplify the aromatic profile of meads, the authors calculated an odor activity value (OAV) for each mead, calculated as the ratio between the concentration of each compound and its perception threshold. An OAV greater than 1 were considered contributors to the aromatic profile of the mead.

Sensory evaluations of the different treatment meads were also performed. The panel consisted of 10 panelists, between the ages of 30 and 50 (4 women and 6 men), who all had wine tasting experience and were trained in the evaluation of honey meads. Each panelist evaluated visual characteristics (turbidity and color), aroma characteristics (quality and intensity), and taste characteristics (quality and intensity). General acceptability was also determined.

Results

Honey Must

• The addition of pollen corresponded to a probable increase in the alcohol content of the mead
• Total acidity and tartaric acid were increased by pollen addition
• pH remained constant
• The increase of acidity was due to weak acids
• The addition of pollen increased the total polyphenol index by 0.130 absorbance units per gram of pollen
• Brown and yellow colors of the must were enhanced
• The addition of pollen increased the turbidity and YAN levels
• According to the authors, pollen is a major source of YAN and could be used to enrich nitrogen-poor media
• Each 10g/L of pollen added provided an average of 70% of the amino acids that were already present in 1L of honey must
• YAN levels in the 40g/L and 50g/L (pollen) meads were above 140mg/L, which is the minimum amount necessary for completing fermentation in grape musts
• These results indicate that pollen provides a good supply of amino acids for completing honey must fermentation

Fermentation Kinetics

• In all treatments, when fermentation was complete, residuals sugars were less than 0.6g/L
• In the control mead (no pollen added), fermentation lasted 6 weeks, indicating that honey alone is deficient in nutrients required for yeast fermentation
• Compared to the control mead, fermentations supplemented with pollen showed a significantly increased fermentation rate, and a reduction in time to reach a maximum rate
• Honey must with more than 30g/L of pollen added showed the highest fermentation rates and the shortest maximum time
• Increases in the fermentation rate were correlated with an increase in YAN levels and turbidity values, which resulted in the overall improvement of fermentation kinetics.
• It is possible that the high polyunsaturated fats found in the pollen may have also contributed to the increased fermentation rate since these compounds are metabolized by yeast cells during the fermentation process.
• The fermentation efficiency of the control mead was approximately 81%
• The addition of pollen improved the fermentation yield and efficiency by more than 7% and 10%, respectively

Physicochemical Characteristics

• The total acidity of the mead decreased with pollen addition
• The final pH increased to more than 4.0 with pollen addition
• The authors suggest this higher pH value might reduce the microbial stability of the meads, thereby justifying the need to adjust the final pH accordingly.
• Volatile acidity increased with pollen addition
• The yellow hue of the mead increased with pollen addition
• Total phenolic index increased with pollen addition
• From these results, it seems that pollen not only increases fermentation kinetics but also improves the overall physiochemical characteristics of the final mead.

Aromatic Characteristics

• Isoamyl alcohols, acetaldehyde, and methanol increased with pollen addition
• There was no correlation between the amount of pollen added and the total minor volatiles present
• The main contributors to the minor volatile component of the meads were alcohols and acids
• All other aromatic families of compounds increased with pollen addition
• Pollen addition significantly increased the proportion of acids in the meads’ aroma, specifically octanoic and hexanoic acids
• The addition of pollen increased the proportion of esters, particularly ethyl succinate and phenyl ethyl acetate, resulting in an increased fruity odor
• The addition of pollen increased the proportion of aldehydes in the mead
• To summarize, the addition of pollen was associated with increased values for all aromatic groups (particularly the fruity and oxidative groups), regardless of the amount of pollen added to the must.
• Meads with 20 and 30g/L pollen added showed the highest contribution to the fruity aroma, and lowest contribution to the oxidative aromas.

Sensory Characteristics

• The most acceptable meads were the 30 and 40g/L meads, which showed the highest flavor and aroma ratings.
• The most significant difference between all the meads was the color. With increasing pollen added, the more the mead changed from a pale yellow to an amber color.

• Aroma notes:

  • The control wine had floral notes, as well as vinegar-like characteristics, which decreased acceptability.
  • The 10g/L pollen mead had notes of “medicinal” and “floral”
  • The 20 and 30g/L pollen meads had notes of almond, dried fruit, apple, caramel, and sweets, with a bit of pineapple on the nose.
  • The 40g/L pollen mead had the strongest notes of honey
  • The 50g/L pollen mead had notes of toast, bitter almond, and honey
  • Mouthfeel increased as pollen addition increased

• Flavor notes:

  • The 40 and 50g/L meads were noted for sweetness, with honey and floral flavors
  • The 30g/L meads were noted for sourness
  • The 20g/L meads had hints of bitterness

In Conclusion

According to the authors of this study, the results show that pollen can be a good activator of alcoholic fermentation in mead, which results in an improvement in fermentation kinetics and improved physiochemical and sensory characteristics of the finished wine. Based on their analysis, they came to the conclusion that the optimal dose of pollen to the honey must is 30g/L. This allows optimization of the fermentation process, while not using an overly excessive amount of the resource.

Personally, I have experimented with bee pollen for mead fermentation in the past and now utilize Fermaid O as a yeast nutrient. As I delve deeper into research behind supplementing with bee pollen, I will certainly start to replace some of those Fermaid O additions with pollen to see how it changes the final product.

SOURCE: Roldán, A., van Muiswinkel, G.C.J., Lasanta, C., Palacios, V., and Caro, I. 2011. Influence of pollen addition on mead elaboration: Physiochemical and sensory characteristics. Food Chemistry 126: 574-582.

Doi: 10.1016/j.foodchem.2010.11.045