ingredients for buttermilk


©David B. Fankhauser, Ph.D.,
Professor of Biology and Chemistry
University of Cincinnati Clermont College,
Batavia OH 45103
add milk to starter
Use 1 part active 
buttermilk as starter

This page has been accessed Counter times since 26 July 2000.
20 July 98, 5 April 1999, 26 July 2000, 22 Feb 03
 Add 4 parts of 
fresh milk to the starter
Sour Cream Buttermilk from scratch
Old fashioned buttermilk
Churning butter
 Microbiology of butter

Cultured buttermilk is probably the easiest and most fool proof fermented milk product to make.  (Note that cultured is different than "old fashioned buttermilk.")  All you need is active cultured buttermilk for the starter, and fresh milk for it to act on (store bought is fine).  The formation of buttermilk is based on the fermentation by the starter bacteria which turns milk sugar (lactose) into lactic acid.  As lactic acid is formed, the pH of the milk drops and it gets tart.  Milk proteins, most notably casein, are no longer as soluble under acid conditions and they precipitate out, causing what we recognize as clabbering.  Thus the two marked characteristics of buttermilk, its tartness and its thickened nature, are both explained by the presence or the action of lactic acid.  Additional by-products of fermentation give subtle variations in buttermilk flavor.

The acidity of buttermilk also explains its long refrigerator shelf life. Acid is a natural preservative because it inhibits the growth of pathogenic bacteria.  Thus buttermilk keeps easily for weeks in your refrigerator. If you keep it longer, it may develop mold on the inner walls of the jar. This mold belongs to the same group of fungi which grow on cheese and is not dangerous. Remove it and the buttermilk can still be used for baking.  However, because the desired bacteria may have died in older samples, buttermilk older than three to four weeks may not work as an inoculum to make buttermilk.

SOUR CREAM can be made with the same procedureas buttermilk, using one cup of cream mixed thoroughly with 2 Tbl fresh active buttermilk and letting it sit for 12-24 hours at room temperature. The higher butterfat in the cream, the thicker the finished sour cream.


6-8 ounces active cultured buttermilk
        Check the label: it needs to say cultured buttermilk, and is not out of date.  (The bacteria die down over time)
3 cups whole milk (store bought works. 2% or skimmed too, but less rich.)
very clean 1 quart container with secure lid (I prefer Mason jars).
Add a bacterial starter of 6 to 8 ounces of active fresh cultured buttermilk to a clean quart jar.  Use 6 ounces if you are certain of the freshnessof the starter (a ratio of about 1 part starter plus 4 parts milk).  When in doubt, use a full cup of buttermilk as starter (a ratio of 1 part starter plus 3 parts milk).
Fill the jar with fresh milk.
Screw on the lid securely and shake to mix thoroughly.  Label with the date.
Let sit out in a warm part of the room until clabbered (here next to our wood stove).  It should be thickened in 24 hours.  If it takes longer than 36 hours, the starter was no longer active (the bacteria had died).  The buttermilk may or may not be tasty if it takes longer than 36 hours.  (If in doubt, it can still be used for baking.)
24 hours later (at room temperature), the bacteria have fermented the milk, the lactic acid causing the milk proteins to clabber.
When finished, the thickened buttermilk coats the glass.  The finished buttermilk should be refrigerated.  It keeps easily for weeks.  Fresher buttermilk makes better starter for cheese.

* "Cultured buttermilk," commonly available in US supermarkets, is not the same as "old fashioned buttermilk," about which I get many questions.  The latter is the liquid which remains after churned butter is removed.  The two buttermilks bear few traits in common. See the following description of churning butter for the differences.

In "olden times," farm families would let freshly milked milk sit for half a day and skim off the cream which had risen.  This cream would be set aside in a cool place, around 50-60 F.  Each milking's cream would be added until several gallons had accumulated.  In the meantime, naturally occurring bacteria in the cream would cause it to slightly sour.  This souring increases the efficiency of churning.  The accumulated, slightly sour, cream would be churned at the optimum temperature (approximately 58 F) such that the butter was firm enough to separate out, but soft enough to stick together into a mass.  The butter was removed, washed in very cold water to remove the remaining milk, and salt worked in to preserve it.  The remaining liquid after the butter was removed was called buttermilk.  I call it "old fashion buttermilk,"  which is slightly sour, has the consistency of  milk, but is slightly paler.  It has flakes of butter floating in it.  Commercial manufacturers sometimes add colored "butter flakes" to imitate the old fashioned buttermilk.  However, the two products are very different, cultured buttermilk being thick and tart, old fashioned being thin, and slightly acid, depending on how sour the cream got before it was churned.

See the page on Smearing and Staining of Bacteria to learn how to see these bacteria with a microscope, and the page on Milk Fermenting Bacteria for a demonstration and discussion of Streptococcus lactis, which is the bacterium which performs this fermentation.  Below is a photomicrograph of buttermilk which has been smeared and gram stained.  Cells of  Streptococcus lactis can be seen as purple spots in a row. Casein is the pink mass covering most of the image.

Gram stain of buttermilk (1000x), showing Streptococcus lactis (purple)
with a pink background of milk protein (casein)

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