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July 2017 WINES&VINES 55 PRACTICAL WINERY & VINEYARD WINEMAKING Another important consideration for spon- taneous fermentation is pH, as high pH can influence the microbial population and its proliferation in the must. Many spoilage bac- teria are favored by high pH, especially some heterofermentative lactic acid bacteria (LAB). Other aspects related to must composition (such as the availability of amino acids, specific lipids, vitamins and minerals) require further study. What we do know is that the nutrient requirements of many non-Saccharomyces yeasts are different than the traditional wine yeast strains of S. cerevisiae. The most important (and simple) measure- ment to take is Brix, which will inform deci- sion-making for or against a spontaneous fermentation. Choosing to continue with spon- taneous fermentation of high-Brix must is not out of the question, but sequential inoculation with a commercial starter culture after an initial fermentation period is a safe recourse. Skin contact: Skin contact is standard practice for red wines. For spontaneous fer- mentation of a white wine, it may be benefi- cial to allow some time for native yeast population to infuse the must after pressing. Instead of sloshing a concentrated bucket of yeast paste into a tank, you are now relying on a film of yeast on grape skins to be re- leased into the juice. A short incubation period (one or two hours) at 40° F after de- stemming and before pressing may increase the transfer of native species yeast from grape skins to must. Know your microbes Although this is not a feasible objective at present, consider this aspect when looking to the future: Not all winemakers have the privilege of knowing exactly which species of yeast and bacteria dwell in their vineyards, as these analyses are costly and require spe- cialist services. Microbial populations also fluctuate over time and differ between vin- tages; they are strongly influenced by viticul- tural practices, especially vineyard sprays, regions and sub-regions. 7 Cost-effective routine microbial diagnos- tics are on the horizon and primed to be a potentially transformational technology in the wine industry. Imagine being able to drop a sample of your crushed juice in a microflu- idics chamber and out pops a list of the dominant microbial species in the juice. This would undoubtedly help to inform the deci- sion whether or not to inoculate with a com- mercial strain as well as which fermentation strategy would enhance the impacts of de- sired strains present in the juice. Far from science fiction, this technology is primed to make its appearance in the next 10 years. Keep a record of the outcomes (successful or not, problems experienced, etc.) of sponta- neous fermentations conducted from your vineyards across different vintages to deter- mine the suitability of your microbial terroir for spontaneous fermentation. Remember to practice good cellar hygiene to minimize the risk of unfavorable species influencing the outcomes of spontaneous fermentations in your cellar. Good cellar hygiene also limits primary inoculation to grape skin-borne yeast. Patience required The species of non-Saccharomyces yeast that are naturally present on grapes at the highest numbers belong mainly to the apiculate yeast A short incubation period at 40° F after destemming and before pressing white wine grapes may increase the transfer of native species yeast from grape skins to must. Fill your bottle selection with... Fill your bottle selection with... a a c w i n e . c o m a a c w i n e . c o m All American Containers Local Inventor y | S uperior S election | E xper t Advice Windsor, CA • San Leandro, CA • Kalama, WA