Do bacteria survive freezing and thawing?

August 5, 2009 12:39 PM

Will frozen buttermilk thaw with its active cultures intact and...well...active? Ditto for yogurt.

I've been experimenting with making cheese the semi-old school way, using buttermilk and/or yogurt with active cultures to provide starter bacteria for acidification. Awesome! Except: I can only find active culture buttermilk in quart containers, I only have time for messing around with cheese on the weekends, and I only need a quarter cup of buttermilk at a time. Lots of buttermilk waste, since the bacteria are only really kicking for a few days.

So - can I freeze it while it's still good and active and thaw as needed? Texture changes don't matter to me, all I need is the bacteria to come through the freezing process able to do their work. My plan is to freeze in quarter cup amounts so I just thaw what I need.

Googling has provided conflicting information. I do cook with buttermilk so it's not REALLY going to waste - but really, there are only so many biscuits and cakes and ice creams a two-person household can go through every week!

posted by peachfuzz to food & drink (7 comments total)

As for the yogurt, from Stonyfield.com:

Does freezing yogurt destroy or alter the effectiveness of the live cultures?
You can freeze a cup of yogurt. A cup of yogurt that has been frozen and thawed will have a different look and texture than fresh yogurt. The cultures become dormant when frozen, but once thawed either in the refrigerator or by your body heat when ingested; they will become live and active once again. There will be a few cultures that do die, but there are so many billions in our products, that it is truly insignificant.
posted by Sassyfras at 12:47 PM on August 5

It will freeze just fine. Milk proteins (aka caseins) are actually very effective cryoprotectants; they'll protect cells very well against freezing damage - ice crystals etc.
In an old lab I used to work in, I found some old ampoules of cheese starter cultures freeze-dried in skim milk, dating back to the 40s and 50s. Craked one open, rehydrated with some broth, and it grew just fine overnight! Amazing really.
One tip though - don't freeze a thick volume of stuff. The extra time it'll take for it to freeze and thaw really will put stress on the cells. I'd pour some in a ziplock perhaps, seal it up and freeze it flat in a relatively thin layer. You can use a straw too, which can even be heat-sealed before freezing. Just like they do for bull spooge.
posted by Mundungus at 12:55 PM on August 5 [1 favorite has favorites]

But really, there are only so many biscuits and cakes and ice creams a two-person household can go through every week!

I'm dating a Southern boy, so I sympathize with having to have buttermilk in the house at all times. Sometime you might want to try marinating meat in it before breading. I'll let chicken pieces sit in buttermilk for a day, then drain and dredge in a flour/panko mixture: perfect fried chicken. The same process, with thin cut tenderized steaks and a shorter marination period, makes excellent chicken fried steak.
posted by Juliet Banana at 12:58 PM on August 5

I have made yogurt from frozen yogurt stored from the previous batch. I just used an ice-cube tray to freeze about 8 oz. and it turned out quite delicious though perhaps slightly weaker than the previous batch. Go for it!
posted by amanda at 1:47 PM on August 5

Fantastic - exactly the information I was looking for. AskMe, how I love thee!
posted by peachfuzz at 3:07 PM on August 5

I can't probably provide any extra information about the buttermilk and yogurt, but I would suggest the CheeseForum. I've been on there recently for questions I have had with cheese making.
posted by aetg at 5:26 PM on August 5

I know that kefir grains (globbish masses of beneficial bacteria & yeast used to ferment the milk into kefir) can be frozen & thawed; or even dehydrated and used again and be fully active, so I would think yogurt or buttermilk bacteria would be similar.
posted by cuddles.mcsnuggy at 6:00 PM on August 5