What a harvest date tells you and why many bottles leave it off

Pick up most bottles of olive oil and you will find a date telling you when to finish it. Few of them say when the olives came off the tree. That missing date is the one Dan Flynn of the UC Davis Olive Center tells shoppers to look for. He also says most oil does not carry one, and that the better producers tend to print it. Once you know why it matters and why it goes missing, you can compare bottles.

What the date tells you

The plainest thing it gives you is a starting point. A harvest date is when the olives were picked, and UC Davis points out that a best-by date does not give you the same information. The same guide says time, oxygen and light can turn oil rancid. That makes its age worth knowing before you pay.

With that starting point, you can do some simple arithmetic. UC Davis advises using oil within 15 to 18 months of the harvest, and choosing the most recent harvest you can find. An oil picked in November 2025 reaches that window between February and May 2027. Flynn adds that a bottle bought within the year of harvest may last two years unopened. It will still be better used soon after you buy it, and within a couple of months of opening.

Seasons matter too, because the world has two harvests. UC Davis says most California and European oils are harvested from October to December. Most Southern Hemisphere oils come in from May to July. So in June, a Southern Hemisphere oil from the new crop can be only weeks old. A northern oil from the latest crop is already at least six months old. Neither is a problem.

A month can also hint at style. The International Olive Council's tasting method describes pungency as a bite in the throat. It calls that typical of oils made at the start of the crop year, mainly from olives that are still unripe. Its guide for consumer tastings suggests one early harvest oil for its intensity. Next to it goes a delicate oil harvested later, for contrast.

Why many bottles leave it off

The simplest reason is that international rules do not ask for it. The labelling section of the International Olive Council trade standard sets out what a bottle sold to consumers must show. The list includes the product name, country of origin, a lot mark and a best-before date. A harvest date is not on it. Cobram Estate, an olive oil producer, also describes harvest dating as optional and says it is rarely seen.

Blending is the second reason, and the industry says so itself. The North American Olive Oil Association, a trade group, says many oils are blends from different harvests and that listing several dates would confuse people. It requires the brands that belong to it to show a best-if-used-by date instead. European law points at the same limit from the other side. Regulation 29/2012, in the version kept in UK law, lets a bottle show a harvest year only if all of the contents come from that harvest.

People disagree about what that absence means. The trade group argues that a harvest date is an incomplete guide to shelf life, since it says nothing about bottling. It says a best-by date from a reputable producer can account for more. That includes the olive variety, how fast the olives were milled and how the oil was handled. Its example is that Coratina olives keep longer while Arbequina olives are more delicate. Cobram Estate, which has its own oil to sell, takes a harder line. It says brands often blend years to freshen old oil. It also says a best-by date can be a generic two years from bottling, and that an oil could be over a year old by the time it is bottled.

The date tells you age and little else. It cannot show how the oil was stored after picking. That is why Flynn's advice pairs the most recent harvest year with containers that protect the oil from light and bottles that are neither dusty nor shopworn.

How to use it at the shelf

A few habits will get you most of the way, whether or not the bottle you are holding has a date on it.

• Read the form of the date. The European rule shows a harvest as a marketing year or as a month and year. The month is when the oil was extracted from the olives.
• Count forward from the harvest. Fifteen to 18 months is the UC Davis window, and the most recent harvest on the shelf is the one it recommends.
• Check where the oil was made, which Flynn says matters more than where it was packaged.
• Look at the packaging. UC Davis says dark glass, metal tins and bag-in-box containers help block light. Clear plastic offers less protection.
• Buy a size you will use within weeks or a few months of opening. UC Davis warns that a bargain bottle loses its value if much of it goes stale.
• Look for a seal if there is no date. The California Olive Oil Council says its program verifies that a sealed oil comes from the most recent harvest and only from California olives.

If you get the chance to taste before buying, take it. Flynn's last test is to taste and smell the oil. You want a suggestion of freshness and no off-flavors, and a printed date can only point you toward that. Once you get it home, he says to keep it in a cool, dark place. Oil left in the light or near heat loses freshness more quickly.