Eureka, its time for another recipe. Today’s recipe is called Dunkler Nachthimmel (dark night sky) and belongs into the category of Dunkelweizen (dark wheat beer). And this brew is my very first open fermented beer ever. More about that later on. I brewed this recipe before (#31 Dunkelweizen) but used a closed fermenter.
I really like the Brewing TV channel and their videos. So, one day I watched episode number 4 called open fermentation. You should definitely have a look at this episode if you have never used the open fermentation technique before. What I took from this episode is the fact that an open fermentation should lead to a more banana pronounced wheat beer than using the standard (for homebrewers) closed fermentation technique. And since I really like the banana character in a wheat beer, I decided to give this technique a go. It has to be mentioned that a lot of German wheat beer brewers use the open fermentation technique every day. Therefore nothing special in the wheat beer process.
Some further information about the recipe. One special rest is included below, the so called “Ferulasäure Rast”. Ferulasäure, in English ferulic acid, is the precursor for 4-vinyl guaiacol which has a clove aromatic aroma. The conversion from ferulic acid to 4-vinyl guaiacol is then made by the yeast cells during fermentation. One way to improve the clove aroma of a wheat beer is to include a Ferulasäure rest to increase the amount of ferulic acid in the wort. And this rest is done at 45°C (113°F). Another important thing for the Ferulasäure rest is the mash pH. The release of the ferulic acid from the grains decreases at lower pH values. To prevent a lower pH level for this rest, the acidified malt is therefore added after the Ferulasäure rest. Enough of water science and ferulic acid, lets go through the recipe.
| Recipe: | Dunkler Nachthimmer | |
| Numbers: | Volume [L] | 10 (2.6 gal) |
| Original gravity | 12.8°P (calculated 13.8°P) |
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| Terminal gravity | 5.2°P | |
| Color | Around 30 EBC | |
| IBU | 11 IBU | |
| ABV | 4.2 % | |
| Grains: | Munich (14.5 EBC) | 0.5 kg |
| Wheat malt (16 EBC) | 1.4 kg | |
| Pilsner malt (4 EBC) | 0.5 kg | |
| Cara Wheat (900 EBC) | 0.15 kg | |
| Carafa 1 (900 EBC) | 0.03 kg | |
| Acidified malt (4 EBC) | 0.075 kg (added after the rest @ 45°C (113°F) | |
| Hops: | Hallertauer (4.2% AA) | 11.4 g and boil for 60 min |
| Yeast: | #1084 Irish Stout | |
| Water: | Burgdorf | Mash: 7.5 L (2 gal), sparge: 10 L (2.6 gal) @78°C (172°F) |
| Rest: | Mash in @47°C (117°F), 20 min @ 45°C (113°F), 15 min @ 53°C (127°F), 30 min @ 63°C (145°F), 10 min @ 78°C (172°F) | |
| Boil: | Total 60 min | |
| Fermentation: | Primary | 7 days @ 20°C (68°F) in an open plastic fermenter |
| Secondary | 7 days @ 20°C (68°F) in bottles | |
| Maturation: | Carbonation (CO2 vol) | 3.5 (carbonated with table sugar) |
| Maturation time | 3 weeks | |
03/24/12: Brew day. All went according to the protocol. Iodine test was negative and the sparging went very well (for a what beer). After boiling the wort with the Hallertauer hops for 60 min, the wort was cooled down to 20°C (68°F) and added a yeast suspension of Wyeast’s #3068 Weihenstephan yeast. The Weihenstephan yeast originates from my yeast library. I banked the yeast in June 2010, and the yeast is still active after nearly two years in the isotonic sodium chloride solution. So I transferred 5 mL of the isotonic NaCl solution in a 100 mL 10°P DME (dry malt extract) starter six days before the brew day. Then transferred the yeast cake from the first starter into 1 L of a 10°P DME starter a day before brew day. The density of this starter was 64E6 cells per mL at the end. So I added roughly 780 mL of the starter to have the right pitching rate of 5E6 cells per mL. Unfortunately, I forgot to include the starter liquid into my dilution calculations to reach the planned OG of 13.8°P after the boil. The yeast starter therefore diluted my wort’s OG down to 12.8°P. But now I have an additional 780 mL of beer…
Fig 1: Open fermentation is over
After aerating the wort by vigorously shaking the fermenter, I removed the lid and let it sit there without any protection for the whole duration of the fermentation.
The fermentation kicked in within hours and a big kräusen formed after 12 hours. I checked the fermentation after six days, and the kräusen was gone (Fig 1). I originally planned to rack the beer just before the kräusen started to vanish. But I had a pretty busy week and forgot to check the fermentation… So I just bottled the beer after seven days after fermenting. There was a pretty nice caramel, malty and hints of banana smell noticeable.
03/31/12: Bottled the beer into bottles and added sugar to reach a carbonation level of 3.5 vol of carbon dioxide. The terminal gravity of the beer was 5.2°P. This seems to be pretty high compared to other brews. But my previous Dunkelweizen batch (exactly the same recipe) finished at 5.6°P and I had no problem with gushing bottles etc. The bottles will carbonate for a week and then maturate in my refrigerator for three weeks. I hope no other bugs such as Acetobacter got into the wort… So stay tuned for the tasting results!
06/01/12: Tasting
Eureka Brewing 
Good luck! Hope it didn’t get Acetobacter. Open fermentation should give you more aroma I think… hmmm… 3.5 vol is really high. Hope your bottles don’t start exploding.
Hy there. Lets hope for the best. Concerning the carbonation level, I already used 3.5 vol for wheat beers without any exploding bottles. But I have to mention, that my bottles for those wheat beers are bottles from commercial wheat beer breweries. And these bottles are much thicker than the ordinary beer bottles. But you are right with your concern. If you use normal beer bottles, you will probably have some exploding bottles with such a high carbonation level.