Let's look more closely and scientifically: “Any body immersed in a fluid at rest, completely wetted by it or crossing its free surface, experiences a vertical force, directed from bottom to top and opposed to the weight of the volume of fluid displaced” You will of course have recognized the famous Archimedes thrust. It is a verified scientific theory which makes it possible to measure the buoyancy of a body.
The entire calculation is therefore based on the weight and volume of the object, and therefore on its density. We will talk here about the density of the pepper and not the apparent density used in the pepper trade. Bulk density calculates the density of a volume of peppercorns in a container. It does not define the density of a pepper grain because it takes into account the volume of air between each pepper grain. (It serves the pepper trade, and varies in density from 400 to 600 g/l)
According to the report Physico-mechanical properties of black pepper (Piper nigrum L.)S Balasubramanian*, R Kumar1, KK Singh2, T John Zachariah3 & Vikram, Central Institute of Agricultural Engineering, India the intrinsic density of the pepper grain varies between 0.987 and 1.012. The variation is due to the moisture percentage of the pepper. In general, the peppers you find in stores have a humidity percentage of around 10-12%, which gives it a density greater than 1.
This explains why your peppercorns immersed in water sink.
But the famous test tells us that if grains are on the surface, then it is synonymous with poor quality. Let's study the phenomenon closely. There are two related explanations to enlighten us:
- There are some grains which have a density less than 1, and therefore naturally remain on the surface
- There is also a phenomenon of surface tension of water.
A new scientific data must be introduced: the surface tension of water. ( https://fr.wikipedia.org/wiki/Tension_superficielle ) This is quite simply what makes gerrids walk on water. You surely know these insects that we see walking on ponds, ponds or sometimes small streams, certainly seen during our childhood.
A very simple exercise to check this: if you put your peppercorns in a glass delicately placed with tweezers, you will notice that all the grains will float! A small downward force will be enough to make them sink.
It is therefore necessary to exclude the surface tension of the water, having taken care to push each grain of pepper to the bottom of the glass. Most of the time, floating peppercorns experienced this phenomenon and all your grains are at the bottom of the glass of water now. These few recalcitrant grains floating around in no way mean that your pepper was of poor quality.
However, what if there are a few tough peppercorns left floating around? Should we conclude that the pepper is of poor quality? That it would be low in essential oil content?
We can in any case conclude that their density is less than 1. These pepper grains whose density is less than 1 do not sink, Archimedes' thrust keeps them on the surface. Their density is less than 1 because they simply have a lower humidity percentage than those at the bottom of the glass.
However, according to the study by T John Zachariah3, we have at worst grains with a density of 0.987.
According to CODEX CXS326-2017 STANDARD FOR BLACK, WHITE, GREEN PEPPER (NBV PEPPER), the percentage of essential oil is approximately 1.5 to 2ml per 100g of whole pepper. Let's model our peppercorn as a 5mm sphere. So with the volume of the pepper grain and at a density of 0.987, our pepper grain has a variation of 3% by weight (compared to a grain with a density of 1.012). This variation in weight is 0.015 g. According to the essential oil concentration of 2ml per 100g, so we have a variation of 0.0003 ml of essential oil. According to Jacqueline Pham's 2007 Piper Nigrum L Thesis, the density of pepper essential oil is between 0.87 and 0.89. So we have a variation in essential oil weight of 0.000261 grams! This tiny variation would therefore be enough to say that a pepper is of poor quality. In short, it's not serious.
No, a pepper cannot be tested by dipping it in water, that's quite simply charlatanism. This test is not supported by any scientific argument; it attempts to make the rough link between concentration of essential oil, density, density and therefore ultimately the quality of the pepper.