- ReferInentation in bottles and kegs: a rigorous approach called natural or farmer method is based G. Derdelinckx, B. Vanderhasselt, M. Maudoux and J. P. Dufour, on the alcoholic fermentation in the bottle Louvai n-Ia -Neuve/Belg ium of residual sugars non fermented by the yeast during the primary fermentation; the Bottle and keg or cask refermentation was a worldwide technology currently ap• presence of yeast in the bottle is mostly the plied to saturate beer before the existence of the artificial carbonation tech• consequence of the clarification technolo• niques. Actually, it is applied to several well known special Belgian, British and gy of the wine. In modem productions. all German beers of the ale type (Trappists, white beers, some abbey's beers and the fermentable sugars are metabolized by typical strong ales) (18, 19, 20). The purpose of this paper is to rigorously describe the technology, the flavour the yeast and refermentation needs the modifications and the possible troubles occurring by refermentation. addition of a solution containing yeast and sugar; this procedure is actually used in most of the industrial factories producing champagne (bottle refermentation) and Introduction mentation is a usual practice in the sparkling wines (tank refermentation or production of sparkling wines. Bottles Charmat Method). A third system is based Although brewers have certainly prac• containing such type of wines are charac• The authors: Or. Guy Oerdelinckx, Ass. Prof.. B. ticed refermentation as long as winemak• terized by an internal pressure higher than Vanderhasselt. M. Maudoux. J. P. Oufour. Labora• ers we have to st3te that on a scientific 0.3 kg/cm2 (2 - 3 g CO/I). wire des Sciences et Technologies brassicoles. Uni• point of view, this technique is described Several methods can be used to produce versite CathQlique de Louvain. Place Croix du Sud. in more details for winery. Indeed. refer- sparkling wine (I). The oldest technique 2 Bte 7. B-1348 Louvain-Ia-Neuve, Belgium - 1111992 157 on the malolactic fermentation of wines, this procedure is used for the production of Table 1 Evolution of the aminoacid content of a refennented beer bottie(ruDde~·. green wines. Finally, an artificial tech• different conditions (pitching rate and dissolved oxygen) .... ,,:, ,:;:-+-';. nique based on direct CO,-injection for carbonation exists too. - Pitching rate Total amino acids concentration (mg/L) . Historically, we can state that refermenta• and dissolved tion is certainly a very old phenomenon in oxygen fermented beverages; but before the use of 200 103 cells/m 1 1780 1765 cork as a stopper it was impossible to keep and 2 ppm 02 the CO, in the bottle for a long time. Dom Perignon (1638 - 1715), cellarer at the 650 IQ3 cells/m! 1880 1856 1914 .1956 abbey of Hautvillers (France), discovered and 0 ppm 02 this property around 1700 and produced 650 IQ3 cells/ml 1917 1825 1950 the first bottle of refermented white wine and 2 ppm 02 called "Champagne". IQ,ooO 103 cells/ml 2625 2240 2720 . Regarding beer, bottle and keg or cask refermentation was a worldwide technolo• and 2 ppm 02 gy currently applied to saturate beer be• Beer characteristics: Pure malt; original gravity 22 Plato; alcoholic content &.5%.vol.; colour 12;' fore the existence of the artificial carbon• EBC; storage temperature 24°C ation techniques. Actually, it is applied to several well known special Belgian, Brit• ish and German beers of the ale type Fermenting wort can also be used as a shown in Tables 1 and 2 and developed (Trappists. white beers, some abbey's carbohydrate source for refermentation under 2.2. beers and typical strong ales) (18,19,20). and has the advantage for small brewing The true quantity of sugar to use is The purpose of this paper is to rigorously plants that active yeast is already present calculated by following the empiric for• describe the technology. the flavour mod• in the pitching liquor. mula: ifications and the possible troubles occur• The quantity of sugar to use for refermen• ring by refermentation. tation depends on three major parameters: A = 2B - (OJ C + D) the desired CO, content of beer. the quantity of fermentable sugars remaining A: Quantity of fermentable sugar to be added to 1. Technology of referrnentation in beer and the CO, content of beer at the beer to reach saturation value B; start of refermentation. Considering the B: Wished CO, content of beer: The primary objective of refermentation is beer CO, content, we advise values C: Quantity onermentable sugars remaining in the saturation of the beverage: therefore. beer before refermemation (bearing a coeffi• between 5.0 g CO,1l and 8.0 COjI respec• only fermentable sugars and yeast are cient 0.3 since this sugar is generally maltotri• tively to avoid a lack of saturatIon and to ose which is not easily fermemable by yeast needed. Quantity and type of both factors prevent some overfoaming. Even though under re fermentation conditions); are dependent on the desired values (CO, 5.0 g CO,1l can be considered as the lower 0; CO,remaining in beer before bottling. content. flavour, taste). • limit especially if beer is dispensed cold, We have to mention that the original characteristics of beer such as alcohol sometimes values till 9.0 g CO,1l were 1.2. Addition of yeast ascertained without any trouble but such content, colour and ionic balance can high values cannot be recommended. Selecting a yeast to insure refermentation, influence the refermentation: external A parameter particularly important is the the brewer has to take two parameters into characteristics as beer temperature at the CO, content before bottling. This parame• account: yeast characteristics and yeast start of refermentation and the tempera• quantity. ture of the refermentation room also. All ter IS dependent of the fermentation and lagering characteristics of beer. Iffermen• these parameters will be studied hereafter. tation is carried out at room temperature Yeast characteristics (20°C) and without pressure the CO, 1.1. Addition of fermentable sugars Considering yeast characteristics, we concentration in beer is approximatively have to distinguish yeast type and physio• The fermentable sugars added to beer are 1.5 gll; if a pressure is exerted the CO, logical properties of the pitching yeast. generally glucose or sucrose. Commer• increases (for example 4.4 gll by an cially, they are available under different absolute pressure of 2.8 bar); such a Yeast type forms as granulated sugar with an extract technique can also be applied during content of about 100%; syrups are also lagering. Practical advantages are finan• Our scientific and industrial experience available with the following usual charac• cial (reduction of the refermentation time) allows us to suggest a classification of teristics: 66% of extract containing be• and sometimes qualitative (reduction of yeasts used by refermentation based on tween 25% and 90% of fermentable sug• the air content in the bottle neck if the practical considerations. Primarily, we ars, the other fractions are mostly unfer• bottler is not equipped with a vacuum can distinguish brewers who use for refer• men table carbohydrates which increase system). On the other hand we have to mentation the same yeast as for the main mouthfeel of beer. The syrups are dis• mention a weaker flavour enhancement by fermentation, thus of the type Saccharo• pensed by suppliers in heated tanks at comparison with a real bottle or keg myces cerevisiae var. cerevisiae; a second relatively high temperature or in contain• refermented beer. This seems linked to the category of brewers uses a typical brew• ers at ambient temperature but in that case isoamyl acetate and ethyl caproate flavour er's yeast which is different from the yeast the user has to take care of the microbial unit increases observed in beers where used by the primary fermentation, this quality of the solution because contamina• most of the refermentation phase takes yeast is also of the type Saccharomyces tions can have severe consequences (see place in bottles or kegs (increase of CO, cerevisiae var. cerevisiae; a third category 3.3.). content of minimum 3.5 g CO"/l). This is of brewers uses for refermentation a non- 158 11/19921 ~;i 11t' -r -: 7 "" [. ~. ., 106 =€ 8- 6 _. ::!. ~ 6 '" ~ '0 Inoculation r.llC in ceHS/ml. 107 ~ lO 11 ;; 10.' -, 10' >- 5,10 .1 -10' SalUf:Jliun of beer.-\; M_.~_.' Y~~l l,:ontcntof beer A S;J1U(;l!lOn or t-.:<:r B: •••..••• ' Yca.'il COOlcnl of heel B 12 16 20 o I' 16 :!O 24 Time elapsed sio..::cbouling (days) Time: dapsed ~in(,;cbouling (days) Fig. 2 Evolution of the beer saturation in terms of time Fig. 1 Evolution of the beer saturation in terms of time elapsed since bottling of two different beers (strong and elapsed since bottling of a beer inoculated before refer• normal) pitched before bottle refermentation with the mentation with different quantities of yeast cells same quantity of yeast cells Beer characteristics: original gravity 12 Plato; alcoholic Characteristics of beer A: original gravity 19 Plato; alcoholic content 5.1 % v/v; bitterness 20 EBU; total acidity 17 ml content 8.1 % v/v; bitterness 29 EBU; total acidity 29 ml NAOH 0.1 N/1 00 ml; colour 8.5 EBC; storage temperature 24°C NaOH 0.1 N/1 00 ml; colour 11.5 EBC; storage temperature 24°C. Characteristics of beer B: original gravity 11.5 Plato; alcoholic content 8.1% v/v; bitterness 29 EBU; total acidity specific brewer's yeast as Saccharomyces dependence and 29 ml NaOH 0.1 N/1 00 ml; colour 11.5 EBC; storage temper• ature 24°C cerevisiae vaT. pastorianus known to that studies trying brewers as baker's yeast.