ENOLOGY NOTES #1
To: Virginia Vintners
From: Bruce Zoecklein
From: Bruce Zoecklein
Subject: Rot degradation of white fruit
This seasons high incidence of rot is causing some obvious problems. Many of you have called for recommendations. The following are some important considerations in white grape processing:
1. Sort as much rot as possible. An incidence level of only 1-3% can negatively influence quality depending on the extent and nature of the rot.
2. Consider whole cluster pressing vs crush and drain. Press lightly or segregate.
3. Cold settle using pectic enzymes and PVPP. The enzymes will help lower the non-soluble solids level. The PVPP will help to bind some of the harsh, low molecular weight phenols which have been extracted do to the rot. Use up to 4 pounds/1000 gal PVPP or 48 gram/hL.
4. Do not add an excessive concentration of sulfur dioxide. Too much sulfur dioxide (greater than about 25 mg/L) will inhibit phenol polymerization and inhibit pectic enzyme activity. Sulfur dioxide will not inhibit most microorganisms at this stage.
5. After cold settling add a source(s) of fermentable nitrogen. Rot organisms, Kloeckera spp. in particular can deplete both fermentable N and thiamine. Use Fermaid K , Superfood and /or other proprietary products followed by DAP after the fermentation has metabolized 2 degrees Brix.
6. Use a vigorous yeast grown aerobically and a higher than normal inoculation volume (5% vs your standard 3).
7. Ferment at an warmer than normal temperature, particularly if you notice some ethyl acetate character in the juice or early fermentation.
If you have already fermented a white wine produced from unclean fruit , examine the wine carefully for both structure (harsh and bitter tannins) and off or spoilage aromas. If you have phenol harshness or bitterness establish fining trials using PVPP immediately. This fining agent works only on very young wines. Aroma problems I suggest that you give me a call and we can discuss. These also should be corrected sooner rather than later.
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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