Impact of Processing Decisions
Impact of Alcoholic Fermentation Decisions
The successful progression of the malolactic fermentation depends in large part upon decisions made during the alcoholic fermentation. Some yeast strains are more inhibitory of the lactic acid bacteria than other strains either because they make more inhibitory compounds or are less likely to lyse and release nutrients post-fermentation. If the malolactic conversion is desired then a yeast strain known to be compatible with the malolactic fermentation should be used. Sulfite use and timing of sulfite addition can also have an impact upon the malolactic conversion. Use of high levels of sulfite early in fermentation can lead to the formation of bound forms of sulfite that retain the sulfite in the fermentation but that are just as inhibitory to the bacteria as free sulfite. In this case the carbon dioxide produced during fermentation will not drive off the sulfite and it will remain in solution and retain its inhibitory potential for the bacteria. Nutrient addition practices can also impact the lactic acid bacteria. If macronutrients are used to stimulate yeast growth the yeast may deplete the micronutrients present in the juice and thereby prevent growth of the lactic acid bacteria. Another important variable is fermentation temperature. Warmer fermentation temperatures favor the bacteria but growth of the bacteria is held in check by the growth of the yeast. If the temperature becomes inhibitory for the yeast the bacteria can bloom, although this generally leads to problems with the yeast fermentation. Acidity and pH adjustment practices can also impact the progression of the malolactic fermentation.
The level of rot in the clusters at harvest is also an important aspect. The lactic acid bacteria do not bloom under these conditions to the same extent as the acetic acid bacteria but will show some growth and will then be present in higher numbers at the start of fermentation. Fruit held in the vineyard longer (late harvest fruit) shows higher levels of surface lactobacilli that fruit harvested at lower Brix levels, so the time of harvest can impact populations of lactic acid bacteria. Finally, as with the yeast, sanitation practices, or more correctly the lack of sanitation practices, can lead to high populations of lactic acid bacteria on the surfaces of winery equipment and in barrel rooms.