Roasted Malt for Distilling: Impact on Malt Whisky New Make Spirit Production and Aroma Volatile Development

Figures & data

Table 1. Summary of observed characteristics of roasted pot still malt (80–220 °C, 0–60 min) and distilled spirit (using 30% roasted malt inclusion).

Parameter	Unroasted pot still malt^a	Minimum value	Maximum value	Model fit^b	Model F-value	Model p-value	Model R^2
	Roasted malt quality characteristics
Hot water extract, dry (L°/kg)	315 ± 5	266	321	Cubic	41.86	<0.0001	0.9448
Cold water extract (% w/w)	21.1 ± 0.3	9.1	40.9	Cubic	8.35	<0.0001	0.7736
Real fermentability (%)	83.7 ± 0.6	49.8	84.7	Cubic	49.28	<0.0001	0.9527
Wort fermentable sugars (g/L)	69.5 ± 0.6	40.6	72.1	Cubic	131.60	<0.0001	0.9818
Elemental N in malt (% w/w)	1.89 ± 0.44	1.4	2.8	Quadratic	4.09	0.0072	0.4402
Wort FAN (mg/L)	154 ± 11	77	163	Cubic	35.61	<0.0001	0.9358
Wort color (EBC)	5 ± 0	4	631	Cubic	86.58	<0.0001	0.9725
Wort pH	5.79 ± 0.02	5.19	5.82	Cubic	78.61	<0.0001	0.9698
1000 corn weight (g)	42.3 ± 1.3	35.4	44.1	2FI	29.33	<0.0001	0.7586
Malt moisture (% w/w)	4.8 ± 0.1	0.2	4.8	Cubic	142.04	<0.0001	0.9831
Wort volume (mL)	289 ± 2	180	298	Cubic	29.04	<0.0001	0.9224
	Production of spirit using high gravity wort (30% of roasted malt inclusion)
	Standard analyses of wort
Wort volume (mL)	209 ± 4	150	218	Cubic	47.89	<0.0001	0.9514
Wort color (EBC)	10 ± 1	9	715	Cubic	99.01	<0.0001	0.9759
Wort FAN (mg/L)	352 ± 9	246	362	Cubic	44.29	<0.0001	0.9477
Wort fermentable sugars (g/L)	141 ± 1	106	142	Cubic	58.49	<0.0001	0.9599
Original gravity	1.0729 ± 0.0004	1.0707	1.0739	Cubic	31.71	<0.0001	0.9284
Final gravity	0.9989 ± 0.0001	0.9985	1.0127	Cubic	180.41	<0.0001	0.9866
Fermentability (%)	82.7 ± 0.1	66.8	83.1	Cubic	181.33	<0.0001	0.9867
Alcohol yield (mL AA/kg malt)	205 ± 3	112	217	Cubic	29.47	<0.0001	0.9234
	Aroma volatiles in new make spirit
2-Methylpyrazine (mg/LAA)	ND^c	ND	11.80	Cubic	39.12	<0.0001	0.9412
2,5-Dimethylpyrazine (mg/LAA)	ND	ND	2.38	Cubic	32.92	<0.0001	0.9309
2-Ethylpyrazine (mg/LAA)	ND	ND	2.28	Cubic	30.76	<0.0001	0.9264
2,3-Dimethylpyrazine (mg/LAA)	ND	ND	0.54	Cubic	99.36	<0.0001	0.9760
Furfural (mg/LAA)	7.2 ± 1.1	4.3	34.30	Quadratic	8.81	<0.0001	0.6287
5-Methylfurfural (mg/LAA)	ND	ND	1.43	Cubic	59.31	<0.0001	0.9604
5-(Hydroxymethyl)furfural (mg/LAA)	ND	ND	4.83	Cubic	12.76	<0.0001	0.8392
4-Ethylguaiacol (mg/LAA)	ND	ND	0.18	Cubic	41.54	<0.0001	0.9444
1-Hexanol (mg/LAA)	1.49 ± 0.01	1.24	3.98	Quadratic	8.83	<0.0001	0.6294
Benzaldehyde (mg/LAA)	0.54 ± 0.03	0.25	1.13	2FI	6.52	0.0017	0.4115

a mean and standard deviation of three samples.

^bModel fit was optimized, and statistical values determined using analysis of variance (ANOVA) (Design Expert 12.0).

^cND – not detected.

Figure 1. Impact of roasting time (min) and temperature (°C) on development of typical malt quality characteristics in pot still malt. (A) hot water extract on dry basis (L°/kg); (B) cold water extract (% w/w); (C) wort fermentability (%); (D) wort fermentable sugars (g/L); (E) wort free amino nitrogen (mg/L); (F) wort color (EBC units); (G) wort pH; (H) 1000 corn weight (g); and (I) wort volume (mL). Roasted malt inclusion rate was 100% in analyses represented in graphs B and H, and 50% in graphs A, C-G and I. Darker tones indicate an increase in the given parameter.

Table 2. Bivariate correlation analysis of roasted malt properties displayed as Spearman’s rank correlation coefficient.^a

	Wort color	Malt moisture	1000 corn weight	Elemental N in malt	Cold water extract	Hot water extract	Wort pH	Wort FAN	Wort fermentable sugars	Real fermentability
Wort color	1.000
Malt moisture	−0.973**	1.000
1000 corn weight	−0.833**	0.809**	1.000
Elemental N in malt	0.160	−0.210	−0.142	1.000
Cold water extract	−0.295	0.357*	0.168	−0.284	1.000
Hot water extract	−0.882**	0.878**	0.758**	−0.185	0.319	1.000
Wort pH	−0.941**	0.936**	0.819**	−0.184	0.410*	0.866**	1.000
Wort FAN	−0.937**	0.943**	0.793**	−0.106	0.297	0.848**	0.940**	1.000
Wort fermentable sugars	−0.948**	0.912**	0.805**	−0.104	0.304	0.922**	0.908**	0.905**	1.000
Real fermentability	−0.896**	0.865**	0.698**	−0.206	0.248	0.912**	0.856**	0.845**	0.879**	1.000

^a Wort samples produced according to EBC methodology with 50% (w/w) roasted malt within the grist.

** Correlation significant at p < 0.01 (two-tailed).

* Correlation significant at p < 0.05 (two-tailed).

Figure 2. Characteristics of high gravity wort (made with 30% roasted malt) as a function of roasting time (min) and temperature (°C): (A) wort volume (mL), (B) wort free amino nitrogen (mg/L), (C) wort fermentable sugars (g/L), (D) wort color (EBC units), (E) wort fermentability (%), and (F) alcohol yield (mL AA/kg malt). Darker tones indicate an increase in the given parameter.

Figure 3. Characteristics of wort prepared with 0–50% roasted malt (140, 180, and 220 °C temperature roasts for 30 min): (A) collected wort volume (mL); (B) fermentability (%); and (C) alcohol yield (mL AA/kg malt). Error bars indicate the standard deviation of triplicate independent samples.

Figure 4. Concentrations of aroma volatiles in spirit (mg/LAA; made with 30% roasted malt, high gravity wort), as a function of roasting time (min) and temperature (°C): (A) 2-methylpyrazine; (B) 2,5-dimethylpyrazine; (C) 2-ethylpyrazine; (D) 2,3-dimethylpyrazine; (E) furfural; (F) 5-methylfurfural; (G) 5-(hydroxymethyl)furfural; (H) 4-ethylguaiacol; and (I) 1-hexanol. Darker tones indicate an increase in the given parameter.

Figure 5. Concentrations of aroma volatiles in spirit (mg/LAA), made including 0–50% of roasted malt: (A) 2-methylpyrazine; (B) 2,5-dimethylpyrazine; (C) 2-ethylpyrazine; (D) 2,3-dimethylpyrazine; (E) furfural; (F) 5-methylfurfural; (G) benzaldehyde; (H) 4-ethylguaiacol; and (I) 1-hexanol. Error bars indicate the standard deviation of three independent samples.