Fl, SA and SI malts were considered unsuitable as barley malt extenders for ... beers, but Fl and possibly SI malts would be suitable for tropical lager beer ...
157
J. Inst. Brew.. May-June, 1982, Vol. 8&,pp. 157-163
MALTING CHARACTERISTICS OF FINGER MILLET, SORGHUM AND BARLEY* By M. J. R. Nout
(Department ofFood Science & Technology, University ofNairobi, P.O. Box 29053, Kabete, Kenya) and B. J. Davies
(Kenya Breweries Ltd, P.O. Box 30161, Nairobi, Kenya) Received 2 7 October 1981
The malting characteristics of the finger millet variety Imele (Fl), sorghum varieties Andivo (SA) and Ingumba (SI) and the barley variety Research (BR) were compared in relation to the brewing of traditional African opaque beer as well as conventional lager beer. The investigations include (a) the effect of steeping and germination conditions, (b) the influence of gibberellic acid and kilning temperature on the activity of important brewing enzymes and (c) an appraisal of the brewing potential of the worts obtained. Fl, SA and SI malts were considered unsuitable as barley malt extenders for conventional lager beers, but Fl and possibly SI malts would be suitable for tropical lager beer manufacture.
Key words:finger millet, sorghum, barley. Introduction Traditional African opaque beers based on sorghum or sorghum-maize mixtures, e.g. Cameroonian Amgba,7 Nigerian Otika24 and South African Kaffir beer,23 fulfil an important demand for low-alcoholic beverages, in particular for the low-income groups. In some cases as much as 30% of the sorghum harvest in Africa is used for malting and brewing.3 In Kenya, the major traditional opaque beer Busaa is prepared from maize and finger millet (Eteusine
coracana). Microbiological and technological aspects of Busaa manufacture were reported earlier.1718 The traditional malting technique of finger millet is similar to that for sorghum7 and includes 24 h steeping by continuous immersion, two to three days germination in 5-10 cm thick layers covered by wet gunny bags, followed by solar dehydration for one to two days, all at 25-3O°C. Much research has been carried out on the germination and malting properties of sorghum in relation to traditional brewing of beer and as a possible replacement of barley malt. i.i3.iwi.2J.2s.3i Apart from early work by Chandrasekhara
et al.,6 little is known about the properties of finger millet as a malting cereal. The aim of this paper is to compare the malting properties of Kenyan finger millet with those of Kenya-grown sorghum and barley, in relation to the manufacture of traditional Busaa, as well as lager beers.
Experimental methods
Samples:—(a) Finger millet (Eleusine coracana Gaertn), local variety Imele (Fl), (b) sorghum (Sorghum bicolor (L) Moench) varieties locally known as Andivo (SA) (red coat) and Ingumba (SI) (white coat) and (c) barley variety Research (BR). Germination conditions.—
Mini scale: Batches of 150 g grain were either (i) steeped
and germinated with continuous water-spraying in a buechner funnel fed by a circulating pump from a constant temperature water-bath, where the water was replaced with fresh water every 24 h, or (ii) steeped until a moisture *Part of this paper was presented at the Fourth Annual Conference of the Nigerian Institute of Food Science & Technology, Enugu, Nigeria, September 1980.
content of 45-46%, after which they were transferred into large glass cylinders closed with vented stoppers for germination.35 The glass cylinders were incubated in a constant temperature water-bath. Kilning was carried out at 50°C at 20 mm Hg for 12 h. The kilned samples were stored at3°C.
Micro-malting: Micro-malting trials were carried out in a Seeger type 115/1978 apparatus as follows: (i) steeping by continuous immersion for 48 h (water changes after 6 and 24 h) at 20°C for BR, SI and Fl, and for 24 h (water changes after 2 and 6 h) at 25°C for SA; (ii) germination at the temperatures as in (i). The grains were turned twice daily and mixed with 30-60 ml water per kg dry grain weight per day; (iii) application of gibberellic acid (GA,, Biocon Ltd) or NaBrO3, was carried out after chit-counts of over 90% had been attained. The required weight of additives was dissolved in 12-5 ml distilled water. This solution was fully absorbed by I kg (dry wt) germinating grains; (iv) all samples were kilned at 50°C air-on for 16-20 h. In kilning trials, 60°, 70°, 80°, 90° or 100°C were applied for 16 h. Analyses
Germinative capacity.—As described by Pollock et al.21 Germinative energy and water-sensitivity.—IOB Recom mended Methods of Analysis.15
Water absorption during steeping.—Excessive water was removed by centrifuging at 1200 rpm for 5 min, after which the moisture content was determined (105°C for 24 h). Root percentage.—Radicles and cotyledons were removed from kilned samples and their weight expressed as a per centage of the total sample weight. Malting loss percentage.—The method described by Novel lie22 was used after removal of the radicles and cotyledons. Malting losses were based on the dry weight. Liquefying power yield.—The a-amylase activity of malt samples was estimated by their liquefying effect on a 8% w/v paste of maize starch (CPC, Kenya) in water, as inspired by Ranum et a/.29 In a Brabender Amylograph bowl, 450 ml distilled water was mixed with 39 g (dry weight) maize starch. Between 0-5 and 10 g of ground sample (quantity depended on activity) was added and the Amylograph test carried out. The reduction in peak viscosity, compared with that of a control of maize starch and water, was expressed in
158
[J. Inst. Brew.
NOUT AND IMVIES: MALTING OF MILLET, SORGHUM AND BARLEY
BU (Brabender Units). The liquefying power yield (LPY) was expressed as BU/g original grain dry weight, as follows:
TABLE I. Effect of Steeping Temperature on Rate of Water Absorption Under Conditions of Continuous Immersion.
(PVc-PVJ-(100-ML)-10*
LPY=-
Time (h) required to reach 45% moisture content
BU/g original grain dry weight where:
PVC
= peak viscosity of control (BU)
PV,
= peak viscosity or sample (BU) = malting loss (%) = sample wt (g)
ML
Ws mcs
R mcn
I5°C Finger millet Imclc (Fl) Sorghum Andivo (SA) Sorghum Ingumba (SI) Barley Research (BR)
= moisture content of original grain (%, as-is)
Modification.—By
determination
of
malt
specific
Diastatic power.—By (a) the EBC method,2 and (b) the IOB Recommended Method.14 DP was expressed as "Windisch-Kolbach (°WK) and °IOB (comparable to °L), respectively, per 100 g original grain dry weight.
Peptone extraction.—Water-insoluble extracted according to Novellie.19
amylascs
were
a- and fi-Amylases.—The contribution of a- and P-amylases to the diastatic power was estimated by inactivating P-amylasc at 70°C in the presence of Ca++ ions.28 a-Amylase was measured by subsequent determination of diastatic power after correcting for slight a-amylase inactivation caused by the heating process. The P-amylase activity was calculated by difference. Proteolytic activity.—AACC method 22-61 ;J0 expressed as mg N/100 g original grain dry weight.
Endo-p-glucanase activity.—The method described by Bathgate5 was used; activities were expressed as IRV units/100 g original grain dry weight.
30°C
35°C
65 48 38 48
40 40 27 37
30 35 20
27 33 18
57
65 60
28
Results
Table I summarises the steeping rate as a function of water temperature. The influence of the method and temperature of steeping/germination, on the visual extent of germination was investigated, and revealed that BR (water sensitivity 26%) performed better using an alternating wet and dry steeping/germination programme, whereas the other grains (water sensitivities 0-4%) gave better germination by continuous spraying. Continuous spraying at temperatures higher than 25°C resulted in dead steeps with BR. For the same reason, the other grains could not be successfully germinated beyond 72 h at 35°C. Malting losses during the mini scale trials were high after prolonged germination, especially in Fl due to the consider able length of the radicles compared to the grain dimensions. Fig. 1 shows the development of liquefying power yield (LPY), mainly representing a-amylase activity, as a function
2SO-I
200
200
ISO
150
100
100
FINGER MILLET 1MELE'
05 'C o
BARLEY
SO
-RESEARCH'
10
10
250
250
200
200
150
150
100
100
50
30
Mashingand wort analysis.—Mashing of a fine grind and determination of extract (% Plato), conversion time (min), clarity, colour, pH, total soluble N (mg/lOOml wort) and nitration time of resulting worts, according to AnalyticaEBC.2 The buffering capacity of 100 ml wort was expressed as ml 01 N NaOH or HC1 required to raise pH from 4-27 to 707.
250
SO
25°C
= moisture content ofsample (%, as-is) = root%
gravity.12
c
20°C
SORGHUM
50
INGUMBA-
SORGHUM •ANDIVO'
10
10
Time, steep + germination (days)
Fig. I. Liquefying power yield as a function of germination temperature and time. O-O I5°C; O-O 20°C;
25°C;
30°C.
Vol.88, 1982]
159
NOUT AND DAVIKS: MALTING OF MILLET, SORGHUM AND BARLEY
TABLE II. Development of Roots, Malting Losses, Liquefying Power Yield and Modification as a Function of Germination Time.
Time1 (days) Finger millet Imclc (Fl)
Root (%)
(%)
Liquefying power yield (BU/g original grain dry weight)
Modication (specific gravity 20°C)
12 6
47 297 384 470 428
■30 •26 ■19 •II •10
6-7 7-7 90 10-2
8-6 110 15-4 19-5 19-7
38 62 180 220 190
107 107 106 104
5 6 7 8 9
3-6 4-8 5-9 7-4 80
9-7 110 12-4 13-8 15-3
141 254 302 289 148
106 104 103 103 103
3 4 5 6 7
1-5 30 50 60 6-5
50 8-5 11-0 130
309 306
•21 •20 16 ■16 114
3 4 5 6 7
0-2 2-2 51 9-5 101
6
7 8 9 10
5-8
Sorghum Ingumba (SI)
Barley Research (BR)
Sorghum Andivo (SA)
Malting loss
0-2 2-7 6-4
11-9
1-02
441 391 365
150
'Steeping + germination.
TABLE 111. Development of Amylases, Proteolytic Activity and Endo-P-Glucanase as a Function of Germination Time. °WK
Peptone extraction
Water extraction I imc1
(days)
°IOB
DP2
a-AJ
P-A
