On a selling website locally there is an item which consists of a pair of demijohn's and some bits and pieces of wine equipment. This includes wine finnings; pectic enzyme; wine tannin; sodium metabisulphate. They are clearly old chemicals and my question is, do they have a useful life at top efficacy and then stop or do they keep going fully effective? I realize that each will age differently. Some will have a use by date should I bin them or use them?
additive age, too old?
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I try not to keep stuff more than one season (year) and typically get what I need around late summer / early fall, just before harvest. All of the items you mentioned, I replace yearly, except tannin. Additionally, many of the chems have an expiration date on them, which I consider as well.
A generalized statement, a chemical that absorbed moisture has a short shelf life an example is potassium sorbate. a chemical that has a high oxidation or reduction potential has a short shelf life, an example is nitrogen flushed potato chips or alcohol in wine. Flavors also readily break down.
most chemicals which are used in wine making are very stable. Ex tannin if it reacts it wants to combine with protein which is not in the plastic bottle, or metabisulphite which wants to ionize in water eventually creating free SO2 (ie you don’t smell SO2 when you open the bottle) or enzymes which are dry/ combined with bovine serum albumin (dehydration and hydration are risk factors)
In the food industry code dates that are in the two year range are picked in part to get you to buy fresh and partly CYA in case there are bad storage conditions as 130F car trunk. Things that have one to two week (bag lettuce/ milk) or three month (chips) actually have some property that is likely to spoil.
most chemicals which are used in wine making are very stable. Ex tannin if it reacts it wants to combine with protein which is not in the plastic bottle, or metabisulphite which wants to ionize in water eventually creating free SO2 (ie you don’t smell SO2 when you open the bottle) or enzymes which are dry/ combined with bovine serum albumin (dehydration and hydration are risk factors)
In the food industry code dates that are in the two year range are picked in part to get you to buy fresh and partly CYA in case there are bad storage conditions as 130F car trunk. Things that have one to two week (bag lettuce/ milk) or three month (chips) actually have some property that is likely to spoil.
Bin them. If you do not know the age, it's not worth risking a batch of wine on an additive with an unknown age.
Bentonite doesn't have a limit, AFAIK -- it's clay, and if it's still powdered, it's good. Tannin is also probably good if it's not clumped. K-meta is an easy one -- make up a gallon of K-meta water (3 Tbsp K-meta, 1 Tbsp acid), take a sniff, and if it rips your lungs out, it's good.
All jokes aside, sniff K-meta VERY cautiously!!! I run a fan when touching my wines to dissipate the fumes.
Everything else? I buy as I need and/or replace it annually. In general I buy in small enough quantities to use things up within a year, which eliminates the question.
YES!! , , , 
