Store cold-pressed oil cool, dark, with the headspace minimised or inert-gas flushed, in an inert container, and with a first-in-first-out discipline. For highly unsaturated oils such as flaxseed and walnut, refrigerated storage is a condition of the stated shelf life rather than a way of extending it.
Why it works this way
Four factors drive deterioration and each has a direct storage answer.
Oxygen is the reactant in oxidative rancidity. Every square centimetre of oil surface in contact with air is a reaction site, so a part-used drum degrades far faster than a full one. Nitrogen flushing at filling and again after part-use is the effective control.
Light, particularly in the ultraviolet and blue range, initiates the free radical chain. Dark glass, an opaque container or an outer carton removes it. Clear packaging under retail lighting has a measurable cost in shelf life.
Temperature accelerates every reaction involved. Excursions are cumulative and irreversible: an oil that spent a week on a warm dock has spent part of its life, and no subsequent chilling recovers it.
Catalytic metals, chiefly copper and iron, accelerate oxidation strongly at trace levels. Food-grade stainless steel, lined drums and inert plastics are the standard; an unlined metal container is a defect.
Unrefined oils also carry residual moisture and fine particulate from the press, both of which promote hydrolytic breakdown. Proper settling or filtration before storage is part of the storage regime, not a separate quality step.
What follows in practice
Write the storage temperature into the specification alongside the shelf life, require the production date on the certificate, and require a peroxide value at shipment rather than only at packing. Cold-pressed seed oils covers the parameters, and what peroxide value measures explains why the number needs a date beside it.