I recently brewed (on 9/2) a kettle soured (soured with lacto P.) Berliner Weiss and my plan is to rack it onto raspberries and lemon zest, thinking that it might lend a nice raspberry lemonade character to the finished beer (since the soured base beer already has a nice clean lemonade-like lactic tartness) , but I am looking for suggestions as far as how to prepare it (to prevent wild yeast from the fruit from impacting finished beer), how much of each to use (I know there are guides for how much fruit to use per gallon, but those are for normal strength beers, whereas the base beer for this is only 3%abv and I would assume the acidity contributed by the lacto also impacts the amount I would need. After taking these factors into consideration, I was tentatively planning to use the zest from 2-3 lemons and about 1 1/2 - 2 lbs of raspberries for a 5 gallon batch, but I would love to get input from this group before doing so. Thanks in advance!
I've never brewed with citrus zest, but here is a recipe from the Mad Fermentationist blog that seems as though it would be relevant to you. (Here are the tasting notes.) It appears he used the zest from 3 lemons for a 5 gallon batch. The tasting notes seem to indicate that this was an appropriate amount to use. (He also dosed a portion of the batch with True Lemon, and ended up not liking it as much as the zest-only portion.) The beer was a Berliner, probably comparable in gravity to yours, so it seems like a pretty apples-to-apples comparison. However, for what it's worth his was not kettle soured and obviously did not have raspberries in it. [Edited to add, as for sanitation, here is an excerpt from a comment that Tonsmeire (the proprietor of the blog) left in response to a reader question (slightly edited for clarity): I wash the lemon with warm water and a paper towel to remove any edible wax and dirt, then peel and toss it in. The alcohol, low pH, and minimal residual carbohydrates make a finished sour beer a difficult place for any microbe to thrive. (me again) Raspberries seem trickier to me, especially if they float (mold could easily grow on the floating mass). I don't have any helpful advice here, just something to consider.]
Obviously it depends on how big your lemons are, but I'd use a "normal" sized lemon per gallon. As to the raspberries, if you want good solid raspberry flavor, you're going to have to increase your ratio, even with a beer that is lower in ABV. I'd think at least 2 lbs per gallon. Since the VAST majority of molds are obligate aerobes, as long as you keep your fermenter micro-oxygenated (as they should be), you won't have to worry about mold.
