This one is actually two experiments at once - first off I tried my hand at 'yeast poaching'; that is, harvesting a proprietary yeast strain (Duvel's, in the case) from the dregs of a bottle. The concept is that since they use natural carbonation, they leave the yeast in the bottle, which you can then harvest and culture up into a full yeast starter.
To do this, I started with an empty vial I had lying around from a previous white labs yeast purchase. I sanitized this vial (Star-San), then drank my Duvel, careful to leave the last ounce undisturbed while pouring. I then flamed the mouth of the Duvel bottle to sanitize it, swirled the yeasty dregs and poured into my vial. I then added small amounts of starter wort (approx 1.040 gravity unhopped 'wort' made up of water, DME, Di-ammonium phosphate and yeast nutrient/energizer), stepping up the amount of total liquid by about 2 fold each time. After a couple of iterations I was able to move up to a 750ml yeast starter, which I then added to the wort to get things going.
Now comes the other part - infusing this beer with blueberries! For whatever reason I've never found a Belgian Tripel with fruit added, but it's subtle malt-centric character and lack of hop bitterness make it an ideal candidate in my opinion. You basically get three choices as a homebrewer: real fruit, pureed fruit in a can, or fruit-flavored extract. I decided to go with the real fruit option, but had done too much work on this batch to risk the whole thing, so I just infused a gallon of it. The first thing I wanted to do was to treat the blueberries to make them as easy as possible for the yeast to digest - I did this by freezing and thawing a half pound of berries 3 times to break up the cell walls, then crushed them up into a sort of mushy paste by hitting the bag with the bottom of a pint glass. I then put the blueberry mash in a covered pot and brought it up to 160F for about 10 minutes to pasteurize it (strains of wild yeast live on fruit naturally and can create some funky flavors if they get into your beer) without cooking off much of the flavor.
I waited until about 36 hours into fermentation (right at the height of it, where there is a large amount of yeast in suspension), then poured about a gallon straight over into a little 3 gallon carboy along with the blueberries (I didn't have any oxidation concerns since I was still at the height of fermentation). This way I was assured to transfer a good portion of active yeast and give them a chance to consume the sugars in the blueberries while fermenting out the rest of the beer. I let it go for a good month afterwards since this beer is pretty big (it came out to 9.3% abv) and I wanted to make sure all those blueberry sugars are consumed so I don't have any bottle bomb concerns later on from incomplete fermentation.
Final results? It was a pretty solid Triple, full of that good belgian clove/banana funkyness, but the blueberry didn't shine through as much as I would have hoped. I think I'd double up the blueberries next time to account for the bigger beer (I used a half pound per gallon based on a blueberry wheat recipe I found, not taking into account that this beer has about twice the grain content). Another problem was that due to the alcohol content, this beer required a good 3-4 months of aging before it was really ready to drink, by which point I think the blueberry character had faded somewhat. I ended up cheating and adding a few drops of blueberry extract syrup to each of the bottles later, which got it tasting great but left me feeling empty on the inside...
Date: 11/19/2009
Size: 5.0 gal
Original Gravity: 1.092
Terminal Gravity: 1.022
Color: 9.8 SRM
Alcohol: 9.3% abv
Bitterness: 33.3 IBU (Modified Rager)
Mash @ 150F for 60 minutes
Ingredients:
10.0 lb Pale Liquid
4.0 lb Pilsen Malt
5 oz Candi Sugar Clear
4 oz Belgian Aromatic
1.0 oz Styrian Goldings (6.0%) - added during boil, boiled 60.0 min
0.25 oz Styrian Goldings (6.0%) - added during boil, boiled 30.0 min
0.5 oz Saaz (5.0%) - added during boil, boiled 15.0 min
0.5 oz Styrian Goldings (6.0%) - added during boil, boiled 5.0 min
750ml Starter of Duvel Yeast (Substitute White Labs WLP570 Belgian Golden Ale). Ferment at 80F and let temperature rise as fermentation progresses to produce Belgian flavor characteristics.
0.5 lbs crushed blueberries added to 1 gallon of above recipe during height of fermentation - would double next time
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