Methanol Mitigation during Manufacturing of Fruit Spirits with Special Consideration of Novel Coffee Cherry Spirits

Abstract

Methanol is a natural ingredient with major occurrence in fruit spirits, such as apple, pear, plum or cherry spirits, but also in spirits made from coffee pulp. The compound is formed during fermentation and the following mash storage by enzymatic hydrolysis of naturally present pectins. Methanol is toxic above certain threshold levels and legal limits have been set in most jurisdictions. Therefore, the methanol content needs to be mitigated and its level must be controlled. This article will review the several factors that influence the methanol content including the pH value of the mash, the addition of various yeast and enzyme preparations, fermentation temperature, mash storage, and most importantly the raw material quality and hygiene. From all these mitigation possibilities, lowering the pH value and the use of cultured yeasts when mashing fruit substances is already common as best practice today. Also a controlled yeast fermentation at acidic pH facilitates not only reduced methanol formation, but ultimately also leads to quality benefits of the distillate. Special care has to be observed in the case of spirits made from coffee by-products which are prone to spoilage with very high methanol contents reported in past studies.

Production of Coffee Cherry Spirits from Coffea arabica Varieties

“…The enzyme pectin methylesterase transforms pectin into pectic acid and methanol [ 36 ]. As fruits contain high amounts of pectin, spirits made from them (such as plums, apples or coffee cherries) also have a higher methanol content compared to distillates made from grains or sugar cane [ 21 ]. Both mashes, YC and YI, showed an almost similar methanol concentration, whereas the value of BT was lower.…”

“…The results of these experiments show that the methanol content could almost be reduced by half compared to a previously produced coffee cherry spirit with a methanol content of 2600 ± 400 g/hL pa [ 18 ]. The use of a very fresh substrate, the short fermentation period and the direct distillation after the end of fermentation may have contributed to the lower methanol content [ 21 ]. However, it must also be noted that the raw material cannot be exactly compared with each other.…”

“…Therefore, studies tried to find solutions to reduce the methanol content in order to obtain a safe and high-quality distillate. They showed that utilisation of different fresh fruit substrates, use of specific yeasts (i.e., strains with low capacity of producing pectin methylesterase), modern distillation or proper distillation techniques could reduce the methanol concentration in fruit spirits [ 21 ].…”

Coffee By-Products as Sustainable Novel Foods: Report of the 2nd International Electronic Conference on Foods—“Future Foods and Food Technologies for a Sustainable World”

“…This may cause problems during fermentation for distilling spirits due to methanol formation. For detailed data, see Blumenthal et al [ 36 ].…”

“…This may cause problems during fermentation for distilling spirits due to methanol formation. For detailed data, see Blumenthal et al [36]. Optimally, organic farming practices should be applied if the leaves or cherries are intended to be used as foods.…”