P - as in PPM analytics
What does PPM stand for?
PPM is the abbreviation for "parts per million" and literally means "parts per million".
How can you imagine PPM?
Parts per million means, for example, that 1 ppm corresponds to one milligram per kilogram. It becomes clearer if you look at a million small polystyrene beads. If you paint one of them red, then the proportion of this red bead among the other 999,999 white beads is exactly 1 ppm. Or consider a 50 liter oak barrel filled to the brim with whisky. One drop from this 50 liter barrel corresponds to 1 ppm. Another example: If we consider a period of 11.6 days, then a single, tiny second in this very long period corresponds to 1 ppm.
What is indicated in ppm?
The proportion of phenols in malt that has been kilned over peat smoke is given in the unit ppm. We obtain this peat-smoked malt directly from Scotland from our supplier Glenesk Maltings in the Eastern Highlands. Of course, the phenols in new make or bottled whisky can also be determined. However, the PPM usually refers to the amount of phenols in the peat-smoked malt.
How do the phenols get into the malt?
When dried peat is burned, chemical compounds such as phenols are formed. During the kilning of malt, these highly aromatic molecules rise with the smoke in the kiln and pass through the moist barley malt. Some of the phenols adhere to the outer shell of the malt grains, the husks, through adsorption.
Which phenols are involved?
There are around 11 phenolic compounds that play an important role in peat smoke malt. These include the basic substance phenol, which gave the entire substance class its name. They also include three methylphenols, the so-called cresols(ortho-, meta-and para-cresol). Alkylphenols, such as 4-ethylphenol and 4-vinylphenol, also play a major role, as does 2,4-xylenol. Finally, the group of guaiacols is also important, including guaiacol, 4-methyl- and 4-ethylguaiacol and syringol.
What are the properties of these phenols?
In their pure form, phenols are solid, crystalline or liquid compounds that can have a characteristic, smoky, phenolic, penetrating, medicinal odor of gauze bandage or hospital. However, the individual phenols have different properties. While phenol and 4-ethylphenol are described as medicinal, guaiacol is described as smoky and tar-like, 4-ethylguaiacol as spicy and sweet and syringol as spicy and sweet-hot. Of the three different cresols, ortho-cresol is described as medicinal, meta-cresol as smoky and rubbery and para-cresol as sulphurous with a smell of sewage. There is also a certain degree of overlap between the respective aromas. For example, a number of phenolic compounds contribute both smoky and medicinal notes to the aroma.
Does the phenol content change during whisky production?
But yes! Phenols are extremely resistant to heat, but their content decreases during the production and maturation of whisky. This is because the second distillation is a very critical step for the phenols. Depending on the alcohol content at which the second cut point is set, which separates the middle run from the after run, a (large) proportion of these aromatic, late-boiling molecules do not reach the heart, but rather the low wines and feints receiver. Depending on the cut point, the fresh distillate then only has around 30 to 70 % of the ppm value in the peat-smoked malt. In addition, some of the volatile phenols are released from the inside of the barrel through evaporation ("angels' share") during barrel maturation. However, some phenols, which are formed as a result of the heat treatment of the cask (toasting, charring) due to the thermal decomposition of the wood component lignin in the wooden staves, can also be released from the distillate during the cask maturation process and enter the whisky in this way. Compared to the phenols from the peat-smoked malt, however, these quantities are relatively small.
How is the peat content in malt measured?
There are various analytical methods for the quantitative determination of the phenol content in peat-smoked malt in ppm. Among the most established are the colorimetric analysis method and the HPLC method.
What is the colorimetric method?
The colorimetric method, or colorimetry for short, is the longest established method for determining phenol content. It is based on the chemical reaction between individual phenols and special chemicals that lead to colored reaction products.
How does colorimetry work?
The phenols adhering to the husks of a weighed quantity of peat smoke malt grains are removed with the aid of a suitable solvent and, in the presence of added reagents (mild oxidizing agent, base), a special chemical, a colour reagent, is added. Its reaction with the different phenols produces a colored solution, which is then analyzed using a special device, the colorimeter.
How do you get from the color to the phenol content in the malt?
As the intensity of the color formed is in direct proportion to the amount of phenols in the peat smoke malt sample, the phenol content can be determined in this way. The colorimeter is set up in such a way that it sends light through the colored solution and then measures how much light of a specific wavelength is absorbed by the colored solution. The phenol content in the unknown malt sample can be determined in the unit ppm using a previously created calibration curve, which was created with color samples of known phenol quantities under the same conditions.
Which color reagents are used?
The so-called Folin-Ciocalteu and Emerson reagents are usually used as color reagents. The former leads to a blue coloration after reaction with phenols, the latter to a red coloration. The Emerson reagent is a chemical compound called 4-aminoantipyrine. It was first described by Edgar Emerson in 1943 as a reaction partner for novel color tests for phenols. Emerson's reagent was also used in the colorimetric method for the analytical determination of phenols in Glenesk peat-smoked malt.
What are the advantages of colorimetry?
The colorimetric analysis method is easy to perform and inexpensive. It provides relatively fast results and is also suitable for analyzing a large number of samples.
What are the disadvantages of the colorimetric analysis method?
The colorimetric method is only specific to a limited extent. The frequently used Emerson reagent does not react with all phenols. Those that have special chemical groups at a certain position in the phenol molecule do not undergo a color reaction with the Emerson reagent, including para-cresol and 4-ethylphenol. Therefore, these specific phenols are not recorded in the overall result and thus not taken into account. In addition, colorimetry can only be used to determine the total phenol content in peat smoke malt. However, this analytical method is not able to determine individual phenols and their individual quantities.
How can individual phenols and their quantity be determined?
Compared to colorimetry, HPLC is a more modern analytical method. It is the more precise and specific method for determining phenols.
What does HPLC mean?
HPLC is an abbreviation and stands for "High Performance Liquid Chromatography". Translated, this means high-performance liquid chromatography.
How does the HPLC method work?
HPLC is based on the principle of chromatographic separation. The phenols adhering to the husks of the malt grains are also removed from a previously weighed quantity of peat-smoked malt using a solvent. A certain amount of this liquid is then injected into the HPLC device. The heart of the HPLC device is a thin stainless steel column. It is hollow on the inside and filled with a special filling material that has different chemical groups. After the liquid with the phenols it contains is injected into the column, it is transported through the entire column with a suitable liquid, the running agent, with the help of a pump. Due to their chemical properties, the phenols contained in the sample interact more or less intensively with the groups of the column packing material. Depending on their own chemical properties, the phenols adhere very little, only slightly, strongly or very strongly to these groups. The individual phenols appear at the column outlet with a time delay according to their individual contact times with the groups of the column material, are recorded by another device, the so-called detector, and displayed graphically by this using suitable software.
What can you see on a graphic HPLC printout?
The profile of an HPLC printout, the so-called chromatogram, resembles an uphill and downhill ride and looks like the profile of a bicycle stage. The individual phenols can be recognized as a mountain or peak, which has the shape of a Gaussian curve. With the recorded times that the respective phenol required to reach the end of the column and by comparison with data from a standard solution under the same conditions, the corresponding phenol can be clearly determined. In addition, the area under the peak, i.e. the Gaussian curve in the chromatogram, shows the quantity of the respective phenol.
What are the advantages of the HPLC method?
This analysis method is very precise and extremely specific, as the individual phenols can be identified and their individual quantities determined in comparison to colorimetry. The only exception: the quantities of the two cresols meta-and para-cresol can only be determined together, as in the vast majority of cases they leave the HPLC column together. HPLC is also less susceptible to interference.
Does the HPLC method also have disadvantages?
Yes, because the purchase and maintenance of the HPLC system are expensive. In addition, the HPLC system can only be operated by specially trained and experienced personnel, which also makes the analyses expensive. Compared to colorimetry, the analysis times per sample are longer with HPLC.
What conclusions can be drawn from the colorimetric method?
Colorimetry is a simple and inexpensive method to determine the total amount of phenols in peat smoke malt. Due to the lack of specificity of the colorimetric method, the PPM values determined do not correspond to the actual quantities in the sample, but are lower with the Emerson color reagent. Colorimetry is therefore only suitable if a rough idea of the phenol content in the peat-smoked malt is sufficient.
What conclusions can be drawn from the HPLC analysis method?
This analytical method detects the individual phenols in the peat-smoked malt and determines their individual quantities. HPLC is very precise and is the analytical method of choice when an exact characterization of the aroma profiles in peat smoke malt is required.
Which method is used to determine the phenols in St. Kilian peat-smoked malt?
Our Scottish peated smoked malt from Glenesk Maltings was previously analyzed using the colorimetric method with the Emerson color reagent and resulted in a peatiness level of 54 ppm. The analysis method was recently changed. Glenesk now has the phenol content of its malts analyzed exclusively using the HPLC method. Incidentally, this is also the standard method of analysis in Scotland. The more precise HPLC analysis method has now determined a total phenol content of 80 ppm for the same peat-smoked malt.
What phenol content will St. Kilian provide in the future?
For the peat-smoked malt that we receive from Glenesk in Scotland, we now state a peat content of 80 ppm instead of the previous 54 ppm, as this new value is determined using the more precise HPLC standard analysis method.
What effects does the change from 54 ppm to 80 ppm have?
None! The new, more precise value of 80 ppm in our Scottish peat-smoked malt does not change the taste of our smoky whiskies. This is because the peat-smoked malt from Scotland is the same and the production conditions in Rüdenau are the same. Only the ppm value is different because it is more precise. And we are happy to pass this on to our customers as information.