How to check and maintain the quality of a hydrolat?

Not all commercial hydrolats are equal. The great difficulty with these products is their lack of stability. Throughout their manufacture, their quality can be impacted: from distillation with the quality of raw materials or distillation parameters, to conservation, but also during packaging in bottles, or by adding additives. To know exactly what is in a bottle of hydrosol, the first thing to do, which may seem obvious, is to read the label. This one gives some interesting elements.

The BIO certification

The label on a bottle of hydrosol gives a few things to gauge its quality. The first, which seems to be the most important, is theorganic certification. Choosing an organic hydrolat is both choosing a product from a environmentally friendly production, but also choosing a product respectful of our health. The products resulting from distillation can indeed concentrate, in the same way as the natural aromatic molecules of plants, certain pesticides or heavy metals. To be sure that the hydrolat is organically produced, simply check for the presence of one of the following two logos on the bottle label: AB or Cosmos Organic.

Choose a hydrolat without preservatives

Pure and natural hydrolats must be composed only... of hydrolat. Many manufacturers add additives or preservatives in order to ensure better product stability. These hydrolats cannot be used in hydrolatherapy, by mouth especially. Due to their composition, their use is reserved for the cutaneous route, for cosmetic uses mainly. Cosmetic regulations require the presence of a list of ingredients on the product, also known as the INCI list (International Nomenclature of Cosmetic Ingredients). This is the list written in English and Latin. Often indecipherable, it provides very interesting information! In the case of hydrolats, it is this list that indicates the presence of preservatives. No INCI list is indicated? Then it is a pure hydrolat, which contains no preservatives.

Favour the 1:1 ratio

The yield of a hydrolat is much higher than that of an essential oil. While several hundred kilos of material are sometimes necessary to obtain only a few milliliters of essential oil, in the case of hydrolats several tens of liters can be obtained with a single small kilo of material. The reference method to obtain a quality hydrolat is to respect the 1:1 ratio. This means that to collect 1 L of hydrolat, only 1 kg of plant will be distilled. This condition makes it possible to obtain a product with a powerful odor, of excellent quality and great therapeutic effectiveness. Some producers do not hesitate to increase the ratio, until obtaining 10 or even 50 L of hydrolat for only 1 kilo of plant, by economic interest. This has the effect of diluting the hydrolat, as well as the active ingredients that compose it, and therefore of diminishing its effectiveness and necessarily its quality.

Pay attention to the name of the product

Several terms can be used to talk about a hydrolat. Only the terms "hydrolat" and "floral water" ensure that it has been obtained by steam distillation. What is the difference between the two? None, except that "floral water" refers to hydrolats obtained from the distillation of flowers, whereas "hydrolat" does not distinguish between those obtained from flowers and those obtained from leaves, for example.

Other terms, however, can be confusing. The term "hydrosol" for example. If it is the translation of the term "hydrolat" in English, a hydrosol in France is a solution in which water is the dispersion medium. It is therefore not a product resulting from steam distillation. The names of flavored water or aromatic water designate products resulting from different processes as well.

Limit the risk of contamination

Importance of microfiltration after distillation

As hydrolats are mainly composed of water, the risks of contamination by bacteria, fungi or yeast are very high. Although hydrolats are sterile when they leave the still, since the temperature is close to 100°C, these germs can develop during conservation. To limit these risks, it is necessary to microfilter the hydrolat, that is to say to make it pass through a filtering membrane whose pore diameter is included between 1 and 0,2 microns. This microfiltration allows to separate the hydrolat from the potential germs it contains. At the time of conditioning, the bottles intended to receive the hydrolats can be also sterilized, with alcohol, with UV, or another process. Pasteurization is to be avoided in order not to impact the intrinsic quality of the product. Finally, microbiological analyses are systematically carried out during the various stages of manufacture to verify the absence of contamination.

Respect the conditions of conservation

Like essential oils, hydrolats are very sensitive to light and heat, but they are also sensitive to oxidation and microbial infections. They keep well between 12 and 15°C but this temperature range is quite difficult to respect at home. The best place to keep them is therefore the refrigerator, which combines darkness and freshness, and thus limits the development of micro-organisms. After opening, it is recommended to consume them quickly, preferably within 3 months. White deposits may form at the bottom of the bottle but they are totally harmless. Other deposits may indicate contamination. A hydrolat that has gone bad will have an unpleasant smell, due to the degradation of the aromatic molecules by micro-organisms. It is then preferable not to use it and to throw it away.

Water quality

Essential oils and hydrolats are obtained by steam distillation or hydrodistillation. The steam will pass through the plant material and take on all the "information" of the plant, all its aromatic and water-soluble molecules. In addition to a good quality plant, the quality of water is inherent to the quality of a hydrosol. Indeed, this one will be, by definition, the water of distillation charged in active compounds. This means first of all that it must be drinkable, filtered and sanitized to allow a use in hydrolatherapy of the products, but also of source, pure and natural preferably.

Molecular composition of hydrolats

The hydrolats contain all the water-soluble molecular fraction of the plant, i.e. the molecules capable of being solubilized in water. As for the aromatic molecules, they contain only 0.1 to 2%. The few analyses carried out on hydrolats show that only certain aromatic molecules known from essential oils are found in hydrolats. This is explained by the composition of the molecule itself, by the functional groups it contains, which will have more or less affinity with water. Indeed, there are in nature molecules called polar and others called apolar. This polarity is defined by the distribution of positive and negative charges within the molecule, and is governed by the geometry of the molecule and the electronegativity of the atoms. In short, it is complex. What we must remember is that two polar molecules will attract each other very strongly, as is the case for two non-polar molecules. Water is a polar solvent, which will attract polar molecules, contrary to essential oils.
In practice, here are the main aromatic molecules found in hydrolats:

  • The acids, because of their carbonyl and alcohol function
  • Phenols: carvacrol, thymol and eugenol
  • The alcohols: partially for some like linalool, alpha terpineol or geraniol, totally for others like lavandulol
  • Coumarins
  • Ketones: camphor, verbenone, thujone, etc.
  • Aromatic and terpene aldehydes
  • Oxides: notably eucalytol (or 1,8-cineole)
  • Linalyl acetate and some ethers like methylchavicol or anethol.

This does not include all the other water-soluble molecules of the plant. At present, very few chromatographic analyses are performed on hydrolats. They still have a lot to teach us! Essential oils and hydrolats having different compositions, they are very complementary since between them they represent a large part of the molecular fraction of the plant.

However, the concentration in aromatic molecules alone would not represent the power of hydrolats. They also have an action at the psycho-emotional and energetic level thanks to their vibratory dimension.

Cohobation and bi-distillation processes

Cohobation and bi-distillation are two different processes but both based on the use of the hydrolat during a second distillation.
The cohobation in the first instance, is a process to increase the yield of an essential oil. For that, a first distillation is carried out to produce the hydrolat and the essential oil which will be then separated, as it is of use to make. Then a second distillation is carried out, this time injecting the hydrolate obtained in the first distillation, in the form of steam. This allows to extract from the plant a larger quantity of essential oil. This process is practiced in particular by certain producers of Rose, to increase the output of its essential oil so invaluable.