To: Virginia Vintners
From: Bruce Zoecklein
Subject: Reduced Volume Formol Titration for Fermentable N, Bleeding Reds, Influence of Clarification on White Wine Composition
Reduced Volume Formol Titration for Fermentable Nitrogen. We have a reduced volume (10 mL) Formol titration method posted on the Enology-Grape Chemistry web site at www.fst.vt.edu/zoecklein/index.html. This procedure will save a significant amount of time when analyzing juice. From the home page go to Extension, then click On-Line Publications, then Reduced Volume Formol Titration.
Bleeding Reds. If you intend to remove some juice from your red must prior to fermentation remember that the juice you bleed will have a different fermentable nitrogen status. The pulp juice which you remove in bleeding has a relatively high concentration of the amino acid proline, which the yeast cannot use. Therefore, adjustments of fermentable N should be different for a red wine fermentation vs. the bleed juice. For additional details see Enology Notes number # 3 posted on the Enology-Grape Chemistry web site at www.fst.vt.edu/zoecklein/index.html. From the home page go to Extension, then Enology Notes.
Influence of Clarification on White Wine Composition. Clarifying juice
improves wine quality when compared to high solids juice. The question is -
what is the optimum level of non-soluble solids for your wine style? Wines
made from too high a concentration of non-soluble solids often have more color, and fuller structure due to a higher phenolic content. The degree of juice clarity also influences the aroma profile. Insufficiently clarified juice can produce wines with reduced varietal aroma and intensity (and excessive reductive tones), while aromas of excessively clarified juice may be dominated by esters which impart dominating banana, soapy and/or artificial aromas (Ribereau-Gayon et al. 1998).
It is difficult to recommend optimum levels of clarity, due to variations in cultivars and desired styles. However, because juice clarity has such an impact on wine style, it should be measured. This is particularly important if you are attempting a consistent style.
For those that have a nephelometer, the measurement of juice clarity is easy.
Those that do not can simply take a representative sample of juice, place in
a 100 mL graduated cylinder, add a few drops of a strong acid and
refrigerate for a few hours. During that time the vast majority of the non-soluble particles will precipitate from solution, and a rough estimation of the concentration can be made.
Dr. Bruce Zoecklein
Associate Professor and Enology Specialist
Head, Enology-Grape Chemistry Group
Department of Food Science and Technology
Virginia Tech, Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: www.fst.vt.edu/zoecklein/index.html
Phone: (540) 231-5325
Fax: (540) 231-9293