Contamination prevention when adding fruits after fermentation.

[javert]

Hello brewers. I'm doing a cucumber version of sour beer (lactic acid addition, so no lactobacillus involved) and was wondering how to avoid contamination from the microbes present in the cucumber itself since they are added after fermentation. Recipe instructions are rather sparse ("add chopped cucumber to the beer") and have no notes regarding the sanitation.
I guess this also applies to other fruits that are added to the fermenter (strawberry, guava, etc) and I suppose asking the microbial flora of the fruit to be nice and behave and not add their own metabolites to the beer is not going to work.
Do you take measures to prevent contamination or is the beer expected to be drank quickly before too much time elapses?
My current plan is to soak the cucumber in some food grade 96 % ethanol before throwing it into the carboy.

 

[VikeMan]

I have never used cucumber in a beer. But I have used lots of fruits. Typically, if they are fresh, I rinse, freeze, thaw, "smush", put them in secondary, and rack beer onto them. Freezing doesn't kill all the microbes, but the freezing/thawing does break down the fruits' cell structure. If I get frozen fruit, I just start with the thawing step. I've never had a beer with noticeable contamination with this prcoess, possibly because the beers' alcohol and pH (and hops when applicable) kept the surviving microbes in check.

 

[sibelman]

Not much experience here, but I wouldn't do the alcohol soak. Just keep it clean - sanitize cutting board and knife, maybe wear sanitized gloves. You have to accept the biota that come with the fruit, but avoid adding other bugs.

Or you could make a cucumber infusion with vodka or purer alcohol, and discard the fruit. You'd lose some freshness though.

I'm a cucumber fan. Post the results!

 

[z-bob]

How attenuative was the yeast you used? If high enough, would a little contamination really do anything; the yeast already ate all the sugar?

 

[VikeMan]

How attenuative was the yeast you used? If high enough, would a little contamination really do anything; the yeast already ate all the sugar?

Well, first of all, different microbes utilize various subsets of the sugar/dextrin/carb universe. So there's never really "nothing" left to eat. But also, there's the fermentable sugars provided by the fruit. (And by priming sugar, if bottling.)

 

[hottpeper13]

I would sanitize the cucumber, knife and cutting board,then chop it up right before transfer.

 

[Steveruch]

I have never used cucumber in a beer. But I have used lots of fruits. Typically, if they are fresh, I rinse, freeze, thaw, "smush", put them in secondary, and rack beer onto them. Freezing doesn't kill all the microbes, but the freezing/thawing does break down the fruits' cell structure. If I get frozen fruit, I just start with the thawing step. I've never had a beer with noticeable contamination with this prcoess, possibly because the beers' alcohol and pH (and hops when applicable) kept the surviving microbes in check.

This. The alcohol and PH are very inhospitable to anything that might cause a problem.
I've never had an issue with adding fruit after primary fermentation in over 24 years of brewing, even in the early days when I was close to clueless.

 

[javert]

Update: added the peeled and chopped cucumbers without seeds into the carboy. Did a slight sanitation by putting them on a zip bag and added a bit of non denatured 96 % alcohol. Left 2 days and a half in which the carboy looked like one of those cool jars of fruit drink.
Beer was kegged and a sample taken. Taste is good, the cucumber dominates but it's rather refreshing. Despite pH being fairly low even for sours (3,3), cucumber mellows it to a mere slight tang. On hindsight, it is one of those insidious drinks whose alcohol isn't felt until after 15 minutes later.
So far so good, now only to wait until it's carbed!
Recipe looks a bit excessive with 1,4 kg per carboy, but so far only good flavors. Now hoping that the cucumber bits don't get stuck while trying to empty the carboy...