Bottle-Culturing: St. Bernardus Blanche

Culturing from a commercial beer is fun, and gives the brewer access to strains of yeast which may not be available otherwise. Obviously this only works if the beer has been bottle-conditioned. Although it is often quoted that some breweries, in a bid to protect their proprietary strains of yeast, do sometimes filter out the yeast before using a different yeast strain for bottling, this is is fortunately the exception rather than the rule.

 In Singapore, most peoples' experiences with Belgian Wit are limited to the ubiquitous Hoegaarden, and perhaps at best Kronenbourg's 1664 Blanc. Don't get me wrong - both are good examples of Wits, but due to the near-extinction of this beer style and its fortunate revival by Pierre Celis, the Belgian Wit has perhaps gone into the equivalent of a genetic bottleneck. I procured a couple of bottles of St. Bernardus Blanche, a fine example of a Belgian Wit, and thought I'd culture the yeast to add to the library.





The bottle was first chilled for several days to allow the yeast to compact down at the bottom. Then, I poured out the beer into a glass, leaving about 1cm of beer and dregs behind.




A vial of starter wort (approximately 40ml) at 1.040 s.g. had previously been prepared in a pressure cooker. I prayed the bottle mouth with some StarSan, swirled the dregs to re-suspend the yeast sediment, and poured everything into the starter vial. Care has to be taken especially in this first step to prevent contamination - unlike a typical step-up for beer fermentation, we're dealing with rather small amounts of viable yeast cells here which may not be able to propagate quickly enough to compete effectively with undesirable organisms.





Next, the entire vial was shaken vigorously for several seconds in order to oxygenate the wort. I opened the cap carefully to allow for gas exchange, then repeated this process for several times until the entire headspace is filled with froth.

The lid was left slightly loose (as the yeast grows it will produce CO2) and stood in a small water bath in order to prevent ants from crawling in. Ideally, the vial should be shaken periodically every hour or so. However, I usually do it twice a day (before I go off to work, and again when I return) and this works fine for me. Now we just wait. If the inoculation was successful, there should be small bubbles heralding the start of fermentation, and eventually the wort should turn more turbid due to the propagating yeast cells.



As the yeast in these bottles are likely to have been stressed from bottling, storage and the alcohol content, I usually allow the first wort inoculation to run for a bit longer than the usual 24hrs. In this case, it was allowed to ferment for 72hrs. I then prepared 150ml of starter wort at 1.040 s.g. in a sanitised 1L Erlenmeyer flask, poured the first vial into the flask and set it on the magnetic stirrer. This was left to ferment for 24hrs, after which a further addition of fresh starter wort was added to top it up to 1L and fermented again for 24hrs. This step is not necessary if you are just looking to ranch some yeast on a slant, but I needed to have a good amount of yeast so that it can also be stored away in my frozen yeast stash.

At the end of it, the entire flask was placed in the fridge in order to chill and allow the yeast to flocculate. After 2 days, a nice compact sediment can be seen at the bottom of the flask. The supernatant was decanted off  carefully (I like to taste a bit of it, just to make sure the culture has not been contaminated), and the resulting yeast slurry at the bottom should be at a rough concentration of 2 billion cells/ml. The yeast was then slanted, and the remaining slurry prepared for freezing.

Hopefully I'll have enough time to brew up a batch of witbier using this yeast!