Definition
A plant extract in which the amount of a pre-chosen marker compound is adjusted to the same value every time. Even the same plant varies in its chemical makeup depending on the soil it grew in, the weather, and when it was harvested. Standardization measures that unevenness against a single yardstick and evens it out.
Why does the same tea taste different from year to year?
Even apples from the same tree differ: the ones that got more sun are sweet, and the ones in the shade are sour. The amount of chemicals a plant holds always rises and falls with the soil, the rainfall, and the season of harvest.
Tea leaves are no different. Even leaves picked from the same field have different amounts of catechins, which give bitterness, and amino acids, which give a savory depth, depending on whether they were picked in spring or summer. So a powder made by simply grinding tea leaves varies a little in composition from one bag to the next.
For people who make drinks and foods, that variation is a headache. If last month's product and this month's product differ in taste and composition, it's hard to sell them under the same name. So a method emerged: after extracting the raw material, you measure one chosen compound and adjust the extract to hit that value. This is the standardization of an extract.
The yardstick: the "marker compound"
A single plant holds hundreds of substances, so you can't even out all of them. Instead, you pick one compound, or a few, that can be measured and that represent the plant, and use them as your yardstick. These are called marker compounds.
Hops, used in beer, are a good example. Hops contain alpha acids, which turn into bitter-tasting compounds when boiled, and the amount varies from year to year. So breweries decide how much hops to add not only by weight but by alpha acid content, and hop extracts are traded at a set alpha acid percentage. Extracts of chili pepper's heat are likewise specified by their capsaicin content.
There are several ways to hit a target content. You separate the compounds with chromatography and measure the amounts, then blend a strong batch with a weak one, or add an excipient (a filler material that adds bulk), until you reach the set value.
Here's a caution. A marker compound is a substance chosen as a yardstick for quality. There's no guarantee that it carries all of the plant's effects, and since only the marker was adjusted, the other substances can still differ from one batch of raw material to the next. That's why standards for medicines, such as the European Pharmacopoeia, reserve the narrow term "standardized extract" for those adjusted to a compound confirmed to be fully responsible for the effect, and classify the rest separately.
To be a bit more precise: concentration ratio and standardization are different things
You sometimes see "10:1 extract" printed on a box. That's a concentration ratio: 10 parts of raw material were used to get 1 part of extract. It only tells you how far the raw material was boiled down.
That number alone doesn't tell you which compounds are in there or how much. The raw material may have held different amounts to begin with, and the solvent used changes which substances come out. And if an excipient is mixed in, the content shifts again even at the same 10:1.
A standardized extract starts from the other end. It doesn't ask how far the raw material was reduced; it fixes what percentage of the finished extract is the marker compound and adjusts to that. So when you read a label, it's more reliable to first check whether the name and content of a marker compound are listed separately, rather than looking at the concentration ratio.
Still, an even content means even quality. It doesn't tell you what the product does in the body. That question has to be answered separately, through research.
Common misconceptions
A 10:1 concentrated extract always has 5 times more active compounds than a 2:1 extract.
10:1 is a concentration ratio: 10 parts of raw material went in and 1 part of extract came out. To know which compounds are actually in it and how much, you need to look at the separately listed marker compound value.
A standardized extract contains every compound of the source plant in the same amount every time.
Only the content of the chosen marker compound is adjusted. The other substances can still vary with the raw material and the process.
Where you meet it
A brewery deciding how much hops to add not just by weight but by alpha acid content, which is how it holds the bitterness of hops that differ every year to the same value.
Specifying an extract of chili pepper's heat by its capsaicin content, so a sauce comes out equally spicy every time it's made.
A supplement label that lists the marker compound and its content separately, such as "extract ○○ mg (contains △% marker compound)". It tells you what's in it and how much better than a label showing only a concentration ratio.
In one sentence
An extract in which the compounds that vary from plant to plant are measured by a marker compound and adjusted to the same content every time. It is not the same thing as a concentration ratio such as "10:1".