Control of Hydrogen Sulphide Formation and Enhancement of the Ethanol Yield in Coconut Toddy - Field Trials

: Field trials werecamedout totestthe finding that theaddition olamrnaniumsalfs, as a source of nitrogen for the metabolism of toddy ycast, auppresscs completely the format-ion of hydrogen sulphide and enhances theethanol yields. Four field trialr carried out, under normal conditions of tapping, showed that h e addition of arnm~nium ultr at a concentration ofO.Q8%(w/v) oPNH4ions to the collection pot prior to tapping increased the ethanol content oftoddy by anaverage of 12.5%and thctofa~ yield aiethanol by an average of 26.5%. At this concentration of NHiions the forma~ion of hydrogen sulphide was atso completely suppressed. Statistical analysis showed that the resutu observed arc of high statistical significance.

The main contributory factor for the off flavour of coconut toddy has beentraced t o the formation of hydrogen sulphide during the natura: fermentatcon Jansz er 01' who h m e d out a detailed study o n this'subject attributed the format~on of hydrogen sulphide in toddy to the metabohc activities of some w~l d yeasts where the sulphur containing amino acid cysteine IS uti@.ed wrth the release of hydrogen sulphide. The mechanism of this process as proposed b y Hough ef all 1s gven in figure 1. Subsequent work o n the control of hydrogen sulphide formation in toddy carried out by Jansz et a12and Kalyananda er 014resu!ted in thediscov~ry of a number of methods for this purpose. Out of these methods the addition of small amounts of arhmoniurn salts t o the sweet toddy before the coffunencement of the fermentation process appeared t o be the sinpkest and t h e most feas'ibie on a commercial scale. The most attractive feature of this process was the increase i n the etbano! yield i n the re'sulting toddy, which was around 25$!&4 . .
Though coconut toddy has been a popular alcoholic beverage for several centuries and also served as the base for tbe distillation of coconut arrack, the problems of undesired flavours and low cthano; yields have remained unsolved. The methods reported earlier such as the use of pure culture fermentation for, increasing the eth,anol yieldj:fiare impracticable on a commercial sca:e. Therefore, the f~ndings of Jansz ef gJ2 and Kalyananda et o r a f t e r extensive research were consikred to be of paramount importance to the coconut toddy industry in solving the above mentioned problems.
These findings were important a s they indicated that the low yields of ethanol and off flavour of coconut toddy could be solved by the simple operation of adding ammonium salts t o the collecting pot during the normal tapping process used on a commercial scale. J -Thefield trialsreported in this paper were carried out to test theappiicabiiity of these findings o n a commercial scale. Adetailed account is presented of four field trials carried out in four different locations and a statistical analysls of the results.

Tapping and Fermentation of Coconut Toddy
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< , Tapping of coconut palms for toddy was carried out by the regular tappers using the normal tapping procedure and schedule. The total number of coconut palms in each field trial were grouped into batches for convenience, and onesample (200 ml) from each batch was drawn for analysis. Control (without added N H 3 and experiments: (with added NH;)trials were carried out on alternate days. The same col:ecfion pot was used for both the control and the experimental tnak for each inflorescence In the experimental trials a calculated amount of ammonium chloride was added (as a solution or in the form of tablets) to the collecting pot at the time of tapping. Each ammonium chloride tablet weighed about (3.6 g and contained 0.20 g of N Hj. The amount of ammonium chloride to be added was calculated based on the volume of toddy collected on the previous day. The number of tablets added was one for every 250 ml of toddy. Thevolume of toddy collected per pot ranged from 250 ml to 2000 m:.
In order to complete the fermentation, toddy samples collected 24 hours after tapping were allawed to stand for another 8-10 hours before anaiysis. However the evolut\on of hydrogen sulphide was monitored right from the time the sarnpies were collected k.

2.2.1
Estimation ofEthylAlcohol -T h e ethyl alcohol content of samples of toddy was estimated by the use of a n Ebulliometer and was expressed as a percentage by volume.
LG.: F o r these field trials a total number of seventy seven (77) trees were used, which were grouped into 9 batches. The effect of adding ~t f 6 on h e yield o f ethana; and the formation of hydrogen sulphide was studied using two concentrat~ons of ammonium chloride. The ammonium chloride was added in the form of a solution and the two conczntrations used were 0.05% (w/v) and 0.08% (w/v) of NH,' based on the vo:~me of toddy.
The results of this field trial are given in Table I Incorporation of N H~ at a concentration of 0.05% (w/v) only oartly suppressed the formation of hydrogen sulphide. I n s o m e batches there was no suppression a t 3% However, the ethanol yield was found to increase appreciab!y and the results showed an average increase of 28% in total yield ofethanol per batch and an average increase of 13.0% in the ethanol content of the toddy. With theincrease ofthe NH; concentration to 0.09% (w/v) a complete suppression of the hydrogen sulphide formation was observed in all batches. At the same time the total yield of ethanol per batch increased by a n average of 46% while the ethanol content in toddy increased by an average of 32%. T h e residual sugar contents of fermented toddy was fdund to be Gery much less in samples treated with NH: (at both concentl-ations) a s cornpared with untreated (control) samples.

Bandulppuwa (Fram 13rh February to 20th February 1979)
In this field trial, ammonium chloride was incorporated into toddy in the form of tablets to give the required concentration af NH; ions. The concentration of ~~i i o n s used was 0.08% (wlv) based o n the volume of toddy expected. The results are given in table 1.

Control of H.vdroge~l Sulphide I;i)rmation in Coco~lut Toddj3
Three hundred and twenty four (314) trees wme used in tkts trial which were grouped into nine batches. In this trial t h e effect of addingNHt ions on the ethanol content of the toddy and the formation of hydrogen sulphtdewas 'studied. The effect of NH; on the total yield of ethanol per batch was not studied The results showed that the suppression of the formation of hydrogen sulp hide in the N H~ treated samples was not complete and also the increase in the ethanol content of toddy was around 7%.
The results of this field trial was affected by the changing weather conditions mainly by the intermittent fall of rain.

Wgdduwa (From 30th Notember to 5th December 1979)
In this field trial, NH; (0.08% w/v) were added to the par in the form of NHiC1 tablets as in the case of the 2nd field trial. The results are given in Table 1.
At this concentration of NH; in the toddy an average increase of 17.1% in the total yield of ethanol per batch and a n average increase o f 6.6% in the ethanol content of the toddy was observed. In addition the hydrogen sulphide formation in toddy was also complete1 y suppressed. In this field trial t o o NH,Cl was added to the pot in the form of tablets to give a concentration of 0.08% (wlv) of NU: based on thr. cxpected yield of toddy. As a result, a n average increase of 14.1% in the total yield of ethanol per batch and an average increase of 4.4% in the ethanol content of the toddy were observed. The hydrogen sulphide formation in toddy was also completely suppressed (Table I).

Statistical Analysis of the Results ,
A statistical atlalysis of the results obtained with respect to (he total yield of ethanol and the ethanol content of toddy is given in Table 2. The average increase in the total yield of ethanol and the ethanol content of t h e toddy were statisticaily analysed to determine the significance of the observed increases. In this analysis the 'Pairedsample Test' was applied. This analysis showed that the observed mean increases in both the ethanol content of toddy and tbe total yield of ethanol were very highly significant.  w h c h contaminates both toddy and the distilled proditet '&dck4givi~grise to off-flavours Furthermore, the ethanol yields obtained by rhe natu&1 fernenration are usually far below the theoretical yields. The low eff~c~ency of sugar utilization under norma' conditions appears to be the main reason for this whichis apparent by the hlgh residual sugar contents observed. The suppiy of an alternative and an easily digestible source of nitrogen in the form of N H~ , as reconlmended by Jartsz etnl' appears to suppress the utilization of amino nitrogen by the wild yeast. As a resulkhe formatron of hydrogen sulphide is avoided, and the utihzat Ion of sugar IS increased resulting In higher yields of ethanol.

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In the field trials carried out to test thu find~ng on a cornmerc~al scale as reported in this paper a mean increase of 26 5% rn the total yeld of ethanol and a mean increase of 12.5% in the ethanol content were observed T h e s~gn~ficance of these mcreases on statistical evaluation showed to he very high I t was necesary ( 1 1 this study to express the increases in the ethanol yelds In terms of both the total y~eld per field trial and the percentage ethanol content of the toddy This was because the percentage ethanol content itself was inadequate to glvea true plcfuredueto dilutron of the toddy by rain water on many occasions. ,?-he high statistical significance of the obscrved trends in these experiments are ifiportant when the highly variable experiments: conditions under whicb the field t$ixk+ we.re conducted are considered, T h e higher increases in the alcohol yields observed in trials la and pafl'icularly in Ih may be attributed to the u e of ammonium chloride in the form of a solution in these t&ls. However, comparative studies on the solubility and mixing of ammoniuni chloride i n the toddy,when it is used as a solcrtioc~or as a tablet, revealed thatcvev in the form o f a tablet ammonium chloride dissolved and mixed adequately in the toddy. Some of the main problems encountered in this study were:  I "a?