[This recipe is the accumulation of many years of playing around and connecting the dots. It will likely make your head spin at first but give it a try. Please, if you have any criticism, leave a comment.]
Fernet Aromatized Maraschino Cherries
Distillers can do more than just make distillates and this exercise explores some of the possibilities. Here we are going to make a modern and very much in vogue version of the alcohol preserved maraschino cherry as well as propose some ways to deepen involvement and eventually refine the process. The exercise will have no explicit recipe because the inputs are so dynamic but rather just guidelines and formulas that never extend beyond simple algebra and can be followed to give a rewarding product.
Lots of research has been done on manipulating cherries, and believe it or not, there is even a one credit course at Oregon State University on the production of non-alcoholic maraschino cherries. The OSU course explores the tricky and certainly novel, but slightly gross process of brining the cherries which will be contrasted with the alternate process used in the exercise.
The often lamented cherries described in the OSU course are brined with preservative sulfites and have their texture enhanced by calcium chloride but that is not the only way to skin the cat. Another exemplary cherry is the Cerise au Soleil of Provence which is relatively minimal in intervention and uses alcohol as the primary preservative. Translated as cherry of the sun, they are aged in jars for the duration of the summer on a clay roof top in the countryside. Alcohol preserved cherries require a fair degree of treatment but nowhere near as much as non-alcoholic versions.
Non-alcoholic maraschino cherries get a bleaching brine primarily to prevent microbial growth but also to remove unsightly browning due to mechanical harvesting. The first bleaching brine features sodium metabisulfite, citric acid & calcium chloride and lasts three weeks while the second bleaching brine features sodium chlorite & glacial acetic acid (crystalized form) and lasts five to ten days. The cherries used in the Cerise au Soleil are thus likely hand picked to avoid bruising which would be readily apparent and preserved in alcohol as a mechanism of respecting their natural color & flavor as best possible which would otherwise be lost. For non-alcoholic cherries, despite aggressive brining, ultimately the sulphite level declines to a point where potassium sorbate and sodium benzoate have to be included in the sugar syrup to maintain stability.
Bleaching non-alcoholic maraschino cherries strips them of most all aroma which eventually has to be replaced and is typically done with benzaldehyde derived from the cherry pits which has the aroma of almonds. Dilution of aroma happens to alcohol preserved cherries when they come to equilibrium with the preserving solution they rest in but is overcome by using a spirit of the same aroma so it essentially diffuses in two directions. This means alcohol preserved cherries are best preserved in Kirschwasser which is a cherry eau-de-vie, but other aromas can also be added which will be explored in the exercise.
The calcium chloride of the first brine, in a certain pH range (which explains the citric acid), reacts with the pectin in the cherries, greatly firming the texture and facilitating mechanical pitting. Alcohol preserved cherries are not firmed with calcium chloride and typically have their pits intact to reduce opportunities for browning. No literature states that alcohol preserved cherries cannot be firmed with calcium chloride and it may be a worth while avenue for exploration. Sulfites reduce enzymatic browning and the mechanism is explained well by the OSU course literature. It may not be possible to pit cherries that have not been brined with sulfites without inducing browning. The browning that does form as a result of mechanical harvesting is not actually bleached by the sulfite brine but is rather bleached by the sodium chlorite brine. To avoid using the brining method, the cherries needs to be as carefully handled as possible.
Sugaring the cherries requires a lot of care and consideration. The cherries need to be sorted by density so they can be uniformly sugared. Not all fruit achieves the same ripeness which means that the fruit from a bushel of cherries will have a wide range of sugar contents. If the cherries were mixed randomly, some would sink in the alcoholic preserving solution while others would float. The cherries that floated above the surface would be subject to more oxidation which is what we are trying to avoid. Cherries can be sorted by first estimating the range of their sugar contents then creating a series of testing bins (sugar-water solutions) to see which cherries float and which sink. The bins can vary by 20 g/L increments. Cherries with higher sugar contents will sink while cherries with lower sugar contents will float. To see where they find equilibrium, the cherries will have to be shuffled between the bins. When there is extreme variance between the sugar content of the cherries and the preserving solution, the cherries with less sugar will lose water and shrivel while the cherries with more sugar will take on water and swell, in both cases causing tissue damage.
To get a rough estimate of a cherry’s sugar content, it is helpful to use a wine maker’s brix refractometer which is a small prism that a single drop of cherry juice can be placed upon. The refractometer has a sight glass with a scale that can measure the sugar content via the refractive index of the juice. A refractometer can measure (estimate) sugar content only in non-alcoholic solutions. The beauty of the refractometer (as opposed to the hydrometer) is that it only takes a single drop to get a reading, but the readings will need to be converted from brix to g/L to make the numbers more intuitive to use. Wine makers use refractometers out in the vineyard to estimate the ripeness of single clusters of grapes as the season progresses while bartenders use them to calibrate their various syrups.
The OSU course teaches a valuable lesson about sugar content which is if it starts at the same level of the cherry it can be walked upwards in slow increments to a desired point without tissue damage. Non-alcoholic cherries typically have a sugar content of 470 g/L which of often more than 3 times the starting sugar content. The sugar content can be increased by 30 g/L every 12 hours until the desired level is achieved which for the exercise may just be high enough that 90% of all the cherries can be brought up to a uniform level.
For alcohol preserved cherries, the sugar content is integral to determining the alcohol content because sugar displaces alcohol lowering the proof. Alcohol fortified products are often brought up to the minimum of microbiological stability by alcohol alone which is typically 18%, but that is not the only approach. An idea in dessert wine production exists which lowers the minimum necessary for alcohol as a preservative by measuring and harnessing the preservative power of the sugar content and sometimes other variables like pressure in the case of sparkling sweet wines. Great research from Maynard Amerine at UC Davis explores this stabilization concept and the lessons learned can be applied to far more than just this exercise. Preservative power is counted in Delle units, named after the Russian inventor, Professor Delle, in the early 20th century and stability is often thought to happen at 80 units. To calculate Delle units the formula A + 4.5C = DU is used where A equals the sugar content in brix and C equals the alcohol content. If a sugar content of 18 brix is achieved, an alcohol content as low as 14% can be used to achieve 80 Delle units. Eighty units is not a hard and fast rule but rather just a point to begin trials and exploration.
An alcohol content at the minimum of stability is critical due to a strange sensory phenomenon where the haptic heft of the solid fruit changes the threshold of perception of alcohol making it seem much more alcoholic than it actually is. This same effect can be seen when eating the pineapple chunks from a Stoli-Doli jar. Many people wrongly believe the fruit holds more alcohol than the liquid, but the illusion is just one of the many phenomena of perception. The same phenomenon will also enhance contrast detection of the fernet aroma we are going to add, and even though fernet will only represent 10% of the preserving solution, eating a cherry may feel as though one is taking an entire shot of fernet.
Many people have the notion that alcohol is a complete preservative, but while it does prevent bacterial growth and certain levels can even kill bacteria, it is powerless against oxidation and even enzymatic browning. If you have ever seen a pear trapped in a bottle of pear brandy, besides the alcohol, ascorbic acid (and possibly sulfites) is also keeping the pear company, otherwise it would brown detrimentally. To preserve a pear, the advice is often given of using 1 g/L of ascorbic acid in the preserving solution (as well as rinsing the fruit and bottle with a sulphuric acid solution to kill bacteria on the surface of the fruit), and with cherries we recommend following the same advice as well as vacuum sealing the canning jars to remove trapped oxygen. Ultra violet light from spending time on clay roofs in the sun may also kill bacteria in the case of the Cerise au Soleil.
Considerations need to be made for the alcohol content of the cherries. When the preserving solution rests with the cherries, the alcohol content will come into equilibrium and be reduced, therefore the displacement of the cherries needs to be known. The displacement of the cherries can be found by taking multiple small samples from each bin that differ by density and placing them in a graduated cylinder of water. The weight of the sample can divided by the observed volumetric displacement to find a ratio which can be extrapolated to find volumetric displacement with only the weight of the entire lot.
Awareness of the Delle stabilization concept can either allow a minimal alcohol content for those that deepen their involvement and experiment systematically or it can just provide a very comfortable margin of error.
Every division of the sorted cherries is going to require its own custom preserving solution and the lowest sugar content cherries need a slightly higher alcohol content if the sugar content is going to be walked upwards. Keep in mind, every 30 g/L increase in sugar content has dissolved volume of 18.9 mL which can dilute the alcohol content by nearly half a percentage point and it may take almost two rounds of increasing the sugar to reach that of your ripest cherries. If you are not making your own cherry eau-de-vie, Hiram Walker’s Kirschwasser is the most practical alcohol base. As a starting point, it may also be useful to put each batch in wide mouth canning jars that assume the cherries will displace the same volume as the preserving solution (one volumetric liter of cherries is preserved in one volumetric liter of preserving solution).
Hiram Walker Kirschwasser is only bottled at 45% alcohol which means that once it is diluted by sugar then brought to equilibrium with the cherries in a 1:1 ratio, the equilibrium alcohol content may be lower than is needed. This problem can be solved by either changing the preserving solution ratio to use more Kirschwasser per volume of cherries or by re-distilling the Kirschwasser to concentrate its alcohol content. Simple tests with water will tell if your cherries can be covered by a desired volume of preserving solution or if adjustments needs to be made.
Introducing additional aromas like the saffron-menthe of fernet can push a preserved cherry into something that is over the top and very special. Fernet cannot be re-distilled with the Kirschwasser because it contains a valuable non-volatile fraction which contributes gustatory-bitterness therefore it has to averaged in. Fernet also has a sugar content of approximately 30 g/L.
If need be, re-distill Kirschwasser on low reflux until the thermometer on the still reads 97°C (the high temperature did not seem to produce a cloudy distillate because it had already been cut previously during the production of the inputs).
Add Fernet to the Kirschwasser so that Fernet’s alcohol content represents only 10% of the blend. At 10% of the preserving solution, Fernet’s 30 g/L sugar content will be diluted to 3 g/L before further dilution. It may be safe to consider this sugar content negligible.
The resultant mixture of Kirschwasser and Fernet will have to be cut to match each specific batch it is going to fortify. First cherries displacing one liter needs to be found. At this experimental scale, a two liter graduated pitcher can be filled to one liter with water and cherries can slowly be added until the water level rises to two liters. This liter of cherries will require one liter of preserving solution. The preserving solution will be constructed to match the sugar content of the sorting bin the cherries were taken from. The displacement of the sugar will need to be found to find the corresponding alcohol content. The dissolved volume of a weight of sucrose can be revealed by dividing the weight by the density of sucrose, 1.587.
To find the corresponding alcohol content we can use the equation: (1000 mL – sugar vol. mL (X%)) = 1000 mL (desired final alc.%).
The X variable represents the alcohol content necessary before dilution by sugar to hit the target alcohol content for a single liter. The volume of alcohol necessary per liter is simply 1000 mL – the dissolved volume of sugar. Working this out per liter means it can easily be scaled for any custom batch size.
Now that the preserving solution has been cut and sugared, ascorbic acid will need to be added and completely dissolved. One gram should be added for every liter of preserving solution. The density of ascorbic acid is 1.65 g/mL thus one gram will displace 0.61 mL and probably can be considered negligible.
After the cherries are added to the preserving solution they should be de-aerated to remove all the oxygen clinging to the cherry skin if possible. Pressure de-aeration in a Cornelius keg is a viable option for large batches and vacuum de-aeration with a canning jar lid attachment is effective for very small batches.
If need be, the sugar content of the cherries should be walked upwards to hit a target and the influence of this addition on the alcohol content should always be a accounted for with simple averaging. If the alcohol and/or sugar content becomes lost, a sample of the preserving solution at equilibrium with the cherries can be re-distilled to reveal the misplaced alcohol and sugar figures.
If the cherries are left unpitted time will eventually cause the alcohol to pull the aroma of the pits into the meat of the cherry. If fernet was added to the preserving solution at the recommended scaling, the same phenomenon of perception that decreases the threshold of perception of alcohol, thereby amplifying it, will also amplify the aroma of the fernet making the indulger believe far more fernet was included than the actual.