Cross Contamination Sour Experiment

The red tape indicates this is a sour jug

Almost half the beers I've brewed over the last 12 months have been soured beers, either in primary, secondary or in the bottle.  When I tell people this the most common question is about sanitation practices and the need for multiple racking canes, carboys, kegs and other brewing equipment.  This is a hard question to answer.  On the one hand mixing these items could result in a infected beer, whole batch or worse.  The real question is to understand how good you are at cleaning your brewing equipment.  It has always been my understanding not to worry about glass cross contamination.  Plastic on the other hand was a dangerous thing, given its porous nature.

Since starting my 1st sour beer last November, I've purchased 5 plastic better bottles for aging sour beers in.  These items were bought on price over the build material and now that my Flanders Red is out and blended I though a little experiment is in order.

Starting out with 4, one gallon glass jugs and one 5 gallon plastic carboy I wanted to test how clean I can get the vessels.  My hypothesis is that the glass would be bug free after cleaning and the plastic would still harbor some Brett, Lacto and Pedio from the past batches.

Cleaning Solution and DME

Here is the history of the test vessels used.

Jug #1:  

History: This is a clear one gallon glass jug used in 3 previous sour blend batches.

Cleaning method:  Cleaned with hot water (120 degrees) and 1 oz of PWB, sitting for 2 hours.  Hot water wash with tap water.  Soaked with a StarSan mixture, no rinse out.

Airbung:  A new, clean 2 piece airlock dipped into StarSan. 

Jug #2:

History:  This is an amber one gallon glass jug used in 1 previous sour batch.

Cleaning method:  Cleaned with hot water (120 degrees) and 1 oz of PWB, sitting for 2 hours.  Hot water wash with tap water.  Soaked with a StarSan mixture, no rinse out.

Airbung:  Previously used one 2 piece sour airlock.  Dipped into StarSan.

Jug #3:

History:  This is an amber one gallon glass jug used in 2 previous sour batches.  

Cleaning method: Cleaned with hot water and StarSan only.  *NO Cleaning*

Airbung: Previously used one 2 piece sour airlock.  Dipped into StarSan.

Jug #4:

History:  This is an amber one gallon glass jug used in 2 previous sour batches.   

Cleaning method:  Cleaned with hot water (120 degrees) and 1 oz of OxyClean Free, sitting for 2 hours.  Hot water wash with tap water.  Soaked with a StarSan mixture, no rinse out.

Airbung:  A new, clean 2 piece airlock dipped into StarSan.

Carboy #5:  *only one carboy used for this test, 5 is it's house number

History:  This is a 5 gallon plastic better bottle used for the past year as a sour aging vessel.

Cleaning method:  Cleaned with hot water (120 degrees) and 5 oz of PWB, sitting for 2 hours.  Hot water wash with tap water.  Soaked with a StarSan mixture, no rinse out.

Airbung:  Previously used one 2 piece sour airlock.  Dipped into StarSan.

Experiment guidelines: 

I created a starter for each gallon jug, approximately 1 cup of 1.020 boiled wort and half a gallon of 1.020 boiled wort for the 5 gallon carboy.  Cooled to around 110 degrees and poured into each vessel.  

The wort was placed into my fermentation chamber at 62 degrees with no yeast added.  This temp was held for 8 days rising 2 degrees a day starting on day 4.  

All airlocks had the approperate amount of water in them, volumes were checked on day 5.  No additional airlock water was needed.

Results:

After the fifth day checking the water level in the airlocks and not noticing any fermentation activity I left the fermentation chamber alone to complete this experiment.  During this time, something perplexing happened.  Jug #2, #3 and Carboy #5 developed a small krousen.  I expected this to develop on the plastic carboy (#5) but not the PBW and StarSan'ed Jug #2.  

Why did this happen to the correctly cleaned Jug #2?  Could I of cleaned this jug incorrectly and gotten lucky on Jug #1?  They were cleaned in the same solution on the same day under the same situations.  I started to look any variables, what could of changed between each jug?  After pondering at the problem I came to a solution.  It has to be the airlock.  The little piece of plastic meant to keep the bugs out of my wort had let me down.  It was the simplest of devices that theoretically could ruin a batch of homebrew.  

My Hyposisthis had held up to my experiment with one major addition.  Correctly cleaned glass with either OxyClean Free or PBW rinsed with a StarSan solution would clean previously use sour glass.  The only exception is your choice of airlocks on a batch of homebrew.

Looking back at my testing parameters, I have 2 flaws in my testing.  One is the plastic carboy test, by having only one test media being plastic I can't determine if the airlock infected the wort, or the plastic itself started the fermentation.  My guess is that they both contributed in starting active fermentation.  But to be sure another test is needed with 2 plastic carboys, one with a new airlock and one with a used airlock.  The second flaw is that I didn't test the wort with a hydrometer.  The reason was I created the first batch of wort and tested that.  It tested at 1.020, I recreated the other batches using the same weight of DME not by gravity readings.

Overall Thoughts:

This test was easy and fun to do and having the extra equipment made it a no brainer.  Understanding that glass, under ideal situations, will not transfer yeast is a good feeling.  Also remember that I do not use any brushes on my fermentation equipment.  Only agitation with hot water and PBW.  These results may of had a different outcome if I used a carboy brush on the glass regularly.  So keep that in mind

Normally I tend to replace my airlocks after 3 or 4 batches and put them into the sour equipment box.  I might have to start replacing them after 2 or 3 clean batches to insure a cleaner fermentation's.  But it is good to know I have no worries transferring my sour batches into a clean glass carboy when needed.  I also feel very strongly that any equipment that is plastic should have it's own sour companion stored at another location.  Including racking canes and transfer tubing.  

If you have any other thoughts or ideas, please post them in the comment box