Of the three main genus of lactic acid bacteria found in wine, Pediococcus is one of the least well characterized. Despite it commonly being found in wines around the world, it is still difficult to answer the simple question ‘what impact will it have on my wine?’ Unlike say Brettanomyces, whose spoilage potential is well described, the spoilage risk that Pediococcus poses and the nature of the spoilage is poorly understood. The most documented spoilage phenomenon caused by Pediococcus spp. is the production of extra-cellular polysaccharides (β-glucans) that leads to ‘ropiness’ in wines. While this type of spoilage is fairly dramatic and detrimental to wine quality, it is also rare (I have never myself seen a ropy wine so if anyone has or has a photo of a ropy wine please contact me). If Pediococcus infection does cause wine spoilage issues it is likely to be in less dramatic fashion than the production of viscous, oily, mucous-like β– glucan strands in your wine. Other spoilage products such as diacetyl and biogenic amines can be produced by Pediococcus but the conditions under which these compounds are produced and the abilities of different strains and species to cause spoilage is not well understood. For example, previous research on Pediococcus in my lab demonstrated that under the same conditions some Pediococcus isolates produced >15 mg/L diacetyl while others produced < 1 mg/L. Furthermore, none of the isolates produced significant amounts of biogenic amines despite all strains growing to very high populations in the wine. There is also conflicting findings on the sensory impact these bacteria may have on a wine with some studies noting that wines infected with pediococci are not always considered spoiled and wines from which pediococci were isolated from were considered to be of high quality by winemakers. Research in my lab supported these findings as a sensory panel rated many of the Pediococcus infected wines higher for desirable descriptors such as ‘floral’, ‘overall fruit’, and ‘red fruit’ aromas than the control wine.
Clearly, there is a range of potential impacts that the growth of Pediococcus in wine can cause but our lack of knowledge concerning the specific impact of pediococci on wine quality makes it difficult to assess risk associated with this bacteria. Furthermore, factors such as warmer growing seasons leading to higher pH grapes and winemakers looking to reduce the use of sulfur dioxide will likely mean an increase in the isolation of pediococci from wines. Because of this, my lab will be starting a new research project this Fall aimed at characterizing the sensory impact of Pediococcus spp. on different wines as well as conditions that promote or reduce formation of biogenic amines. Results from this research will help winemakers better assess spoilage risk associated with pediococci and take appropriate steps. Furthermore, assessing the impact of Pediococcus isolates on the sensory properties of different wines will aid winemakers in diagnosing wine spoilage by pediococci. To aid us in this study, my lab is soliciting wine samples from industry that may contain Pediococcus. Sample origin will be kept confidential and Pediococcus isolates will become part of a culture collection at OSU for use in this study. Please contact me at james.osborne@oregonstate.edu for more information about this research and/or to provide wine samples. — By Dr. James Osborne, Professor and Enology Extension Specialist, Dept. Food Science & Technology, OSU
