A 100g tub of Bentonite by Young's.
Bentonite is a naturally occurring clay used to aid the clearing of cloudy wines. As it swells up in liquid it absorbs proteins in the wine, dragging them down to the bottom thus helping to clear. Best used at the start of fermentation.
Dosage: 1 level teaspoonful per gallon. Mix vigorously in 1/2 cup of wine/water and allow to stand for 15-30 minutes to disperse. Stir again, add to your vessel and swirl.
Keep the lid tightly closed in between uses, store in a dry place.