This looks like the recipe you followed
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Concord Grape Wine
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Makes one gallon.
Ingredients:
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<TD>6 lbs. Fresh Grapes</TD>
<TD>5 pints Water</TD></TR>
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<TD>3 1/4 cup Sugar</TD>
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1 tsp. Pectic Enzyme</TD></TR>
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<TD>1 tsp. Yeast Nutrient</TD>
<TD>1 Campden Tablet, crushed</TD></TR>
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<TD>1 pkg. Wine Yeast</TD>
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Keep your acid tester and hydrometer handy. As with all wild fruit the sugar and acid content varies greatly from year to year and even from one location to another. The recipe above is a general recipe to use which you may have to adjust.
Starting S.G. 1.090-1.095
Acid Level .65%
Directions:
<LI>Wash grapes and remove from stems. Discard modly and badly bruised fruit.
<LI>Put grapes into straining bag.
<LI>Press and squeeze grape juice into primary fermenter. Tie top of straining bag and place in primary fermenter.
<LI>Add all remaining ingredients, except yeast.
<LI>Cover primary fermenter.
<LI>Wait 24 hours, then add yeast and re-cover primary fermenter.
<LI>Stir daily, check S.G. and press pulp lightly to aid extraction.
<LI>When S.G. reaches 1.030 (3-5 days), lightly press juice from bag. Then syphon juice into glass container and attach airlock.
<LI>When S.G. reaches 1.000 (usually about 3 weeks), fermentation is complete. Syphon juice off sediment into clean glass container. Re-attach airlock.
<LI>To aid in clearing, syphon again in 2 months and again, if necessary, before bottling. </LI>
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This would give an ABV of 12-13% depending on the contribution of the grapes themselves, so I don't think you would want to drin the whole gallon in one sitting!