Not too long ago, I read a post online discussing the relationship between social wasps and fermentation (ultimately) in wine. The first thing that I thought, being the ecologist that I am, was “Wow, this is really cool! I need to read the source article and present it on my blog!” My own Masters research focused on nutrition in bees (actually, my exact thesis was “Ecological and Evolutionary Shifts in Pollen Chemistry and Their Implications for Pollinators”), so finding an article related to not only wine but distantly-related wasps as well was extremely exciting for me (I know, I know, I am a huge nerd).
The basis of the research I will present to you today, which was recently published in the Proceeding of the National Academy of Science (PNAS), is that it is still unclear how the yeast, S. cerevisiae (the “wine yeast”) actually spreads around different environments. In fact, studies have shown that before the grapes have matured, there almost no S. cerevisiae present, however approximately 25% of ripe grapes that have been damaged have these cells present.
It is known that S. cerevisiae is not transferred from place to place via the air; thereby some other mechanisms must be in place in order to explain its movement from winery to winery and environment to environment. Some studies have suggested that migratory birds may place a role in this movement; however, since it has been shown that yeast cells do not survive longer than 12 hours in bird guts, it’s unlikely that birds would be a major player in this process. As a result of this, it is suggested that perhaps insects play a role in the movement of yeasts from environment to environment.
Some studies have suggested that social wasps may be a vector for this movement of yeasts from one place to the next, since it has been shown that bees and wasps harbor yeasts in their hives in the fall and throughout the winter. The authors of this study suggest that social wasps may be an ideal vector for this movement of yeast as a result of their relatively complex life cycle. Nests are established in the spring by females, who recently emerged from overwintering (“hibernating”, if you will). The female then feed their young by regurgitating, which the authors suggest is a possible mechanism for transferring yeasts from one generation to the next. Wasp populations are also known to peak around the same time as grape maturation, and it is known that wasps do feed on the grapes themselves. Some wasps are even equipped with mouth parts that are specifically designed to pierce tough surfaces, potentially such as the skins of grapes.
The two main questions that the authors of this study asked were: 1) Can S. cerevisiae cells complete an annual life cycle through transgenerational transfer in social wasps?; and 2) Do social wasps harbor specific yeast strains in their bodies, or do they move different strains about different environments depending upon what is present and where?
What did they find?
Methods: I’m sparing you the nitty gritty details of the methods, as many of them are extremely technical in nature. I will say that the sample size was ample for proper statistical analysis, and upon brief review, everything sounds good to me! In general, the guts of wasps were harvested and examined for the presence of different yeasts, and also technical genetic analyses were performed to identify the yeasts and other organisms present in these guts. If you want to know specific details, please ask me and I’ll do my best to try and find the answer for you!
- 17 S. cerevisiae strains were found in the guts of 61 wasps (4% of the microbial gut community).
- The frequency of the species of yeasts changed depending upon the season.
- Saccharomycodes species of yeasts (including S. cerevisiae) were found to have the strongest relationship between time of collection and yeast presence, specifically when the grapes were ripe.
- In contrast to other species whose presence fluctuated depending upon season, S. cerevisiae strains were almost always present in the guts of wasps.
What about these S. cerevisiae strains found in wasp guts?
- 10 of the strains found were related to wine strains, 3 were related to bread strains, 1 was related to a mix of African beer, palm wine, and laboratory strains, and 1 was related to African palm wine strains.
- The strains isolated from the wasp guts belonged primarily to strains related to those from European grapes and wines.
- The strains of yeast used in wine fermentation at a local winery (in Italy) were found to be genetically different than the yeast strains found in the guts of wasps in nearby vineyards.
- This suggests that wasps may promote yeast biodiversity.
- S. cerevisiae and other yeasts were found in the digestive tract of larvae and newborn workers.
- This suggests wasps are able to “pass down” naturally collected yeast strains to the next generation by way of regurgitation of food.
What do these results mean, and why are they important?
It has been well established that grapes can undergo natural fermentation, even without inoculation of S. cerevisiae in the winery/laboratory. This suggests that there must be yeast present on the grapes in order to achieve this, however, since there is no yeast present on unripe grapes, how do they establish a yeast colony to perform this natural fermentation? According to this paper, the answer may very well come from the wasps. Since S. cerevisiae is continually present in the guts of wasps, and wasps feed on grapes when they have reached a point of ripeness, it is logical to surmise that the act of the wasps piercing the grapes to feed results in a transfer of natural yeasts from gut to grape, thereby facilitating the natural fermentation process in the grape.
Basically, without wasps, natural fermentation cannot start in grapes!
This study also found that overwintering (“hibernating”) females carried yeast cells in their guts and then passed them along to their young in the spring, the process by which is theoretically a continually perpetuating process generation after generation.
In regards to yeast genetics, the study did not find any yeast strains that are native to animal species in the guts of wasps. In fact, the yeast strains the genetic analysis of the yeast strains found in gut wasps reveal that the strains are directly related to wine, grapes, bread, and oak yeast strains.
Finally, the results of this study found that the yeast strains found in the guts of wasps, grapes, and winery of a particular vineyard are very similar to strains coming from other environmental and/or geographical locations. This indicates that social wasps may play a large role in maintaining the genetic and ecological diversity of yeasts. This result is extremely important in regards to conservation efforts, as the conservation of this genetic diversity of yeasts has potential importance within the whole wine industry as well as other fermented product industries.
The authors suggest that any change to the environment that results in the destruction or degradation of yeast genetic diversity may have a large negative impact on the overall quality of wine or other fermented products. To maintain genetic diversity in yeasts and thus increase the complexity and quality of wines, we must make concerted efforts to maintain the diversity of social wasps, and to protect their habitats to the best of our ability.
Overall, I thought this was a really fascinating study, and completely opened my eyes to a “new” part of viticulture and enology that I was not otherwise in tune with. We’ve known that grapes start their own natural fermentation process before beginning the artificial fermentation process in the winery, which contributes to the overall complexity and quality of the finished wine. What I didn’t know was how this natural yeast even occurred on the grapes to begin with. I just assumed the yeasts were just always there, and was unaware that the grapes are pretty much “yeastless” until they have ripened.
This study has opened my eyes to the fact that insects, specifically social wasps, may play a huge role in the initial inoculation of natural yeasts into the grape, which jump starts the fermentation process prior to fermentation in the winery which results in an overall increase in wine complexity and possibly quality. Looks like we have the wasp to thank for much of the complexity in our wines, and that’s pretty amazing if you ask me!
I’d love to hear what you all think about this topic! Please feel free to leave your comments!
Source: Steffani, I., Dapporto, L., Legras, J-L., Calabretta, A., Di Paola, M., De Filippo, C., Viola, R., Capretti, r., Capretti, P., Polsinelli, M., Turillazzi, S., and Cavalieri, D. 2012. Role of social wasps in Saccharomyces cerevisiae ecology and evolution. Proceedings of the National Academy of Sciences (Microbiology). Online before print. DOI 10.1073/pnas.1208362109