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Fermented milk from Iceland

Skyrskyr

Skyr is Icelandic skim milk heated near boiling, set warm with a spoon of old skyr and rennet, then cooled slowly and strained in cloth. Yoghurt bacteria sour it, and on farms yeasts add a fermented note. The result is a very thick, sour, high-protein curd at pH 3.7–4.3.

Fully documentedFermented milk31 h – 32 hFamily: Fresh lactic (acid-set) cheese family

Recipe

Skyr, a photo from Wikimedia Commons
Photo: Schnee ( talk ), CC BY-SA 4.0, via Wikimedia Commons
Amounts from a sourceEach farm batch in the Matís 2011 study made about 2 litres of skyr; one KEA dairy batch made 500 kg. Neither gives a rennet dose.
Fresh milk from the farm's cows, skimmedOne farm in the study used whole milk, which gave a skyr with more dry matter (23.9 %)[matis2011]
Old skyr (skyrþéttir) as starterAbout 1 tablespoonThinned with a little of the warm milk before it goes in[matis2011]
RennetAdded with the old skyr; the report gives no dose[matis2011]
Starterbackslop (old skyr, called skyrþéttir)

Total time across the recorded steps: 31 h – 32 h

Start
Drag the bar or press Play

What changes: The cream is separated off, leaving skim milk

Step 1 of 6
Skim the milk
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented
Which microbes the steps name, step by step
Yeasts
S. thermophilus
L. delbrueckii
Kluyveromyces
Saccharomyces

Output: skim milk.

Flavour
Not documented
Texture
Not documented
Colour
Not documented

Microbes at work in this step

Not documented for this step.

Method

Measured measured in a studySet fixed by a specification or tested recipeReported one source reports itTypical a general value, not sourced for this fermentUnconfirmed not yet checked against a source

At a glance

Skyr is Icelandic skim milk heated near boiling, set warm with a spoon of old skyr and rennet, then cooled slowly and strained in cloth. Yoghurt bacteria sour it, and on farms yeasts add a fermented note. The result is a very thick, sour, high-protein curd at pH 3.7–4.3. Made in 6 steps over 31 h – 32 h. The longest step, strain through cloth, takes 24 h (Valsdóttir Þ 2011). Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus do most of the fermenting.

Key numbers
Main step24 hReported[matis2011]Strain through cloth
Temperature90 °CReported[matis2011]Heat the skim milk
AciditypH 3.7–4.3Measured[matis2011]Strain through cloth

What makes this one different

Skyr is set like yoghurt with the same two thermophilic bacteria, but rennet goes in and the curd is strained to a thick mass. At the KEA dairy it sets at 39–40 °C, and farm skyr carries yeasts from its old-skyr starter.

Milk
Skim cow milk in dairies; farms use skim or whole milk

Related ferments

Variants

  • Dairy skyr from pure cultures (MS Selfoss)No old skyr; a fresh pure culture each time, overnight souring and whey removal by membrane filtration. It is thinner, glossier, smoother and whiter than farm skyr.
  • Whole-milk farm skyrMade from unskimmed milk; higher in dry matter (23.9 %), darker and less glossy than skim skyr.
  • Norwegian skjørNorwegian skjør is a cultured skim milk also called skyr there; it is usually made without cooking and without rennet.

Safety

Skyr is heated near boiling and soured to pH 3.7–4.3. Matís found no moulds in farm or dairy skyr. For strained dairy products, BC food-safety guidance says to strain under refrigeration and to store at 4 °C or colder.

History and sources

Every number is labelled with how it is known. How this atlas is made

Skyr is mentioned in medieval Icelandic sources including Egil's saga and Grettis saga, but no detailed description of the medieval product survives (Wikipedia). Matís (2011) says skyr has lived with the Icelanders for at least 1000 years, and in the settlement age it was probably sourer and thinner than today. Dairy production in the last century changed it a great deal.

  1. [matis2011] Valsdóttir Þ., Reynisson E., Knocke N., Ólafsdóttir A., Sveinsson Þ.E. 2011, Hefðbundið skyr (Traditional skyr, homemade and industrial compared), Matís report 09-11paper
  2. [tp] Tetra Pak, Dairy Processing Handbook, chapter 13 Fermented milk products (concentrated yoghurt, including skyr)book
  3. [bc-yogurt] FOODSAFE BC with the BC Ministry of Health, BCCDC and Fraser Health, Guidelines for the Production of Dairy Products in Food Establishments, Yogurt sample documentation, September 2022gov
  4. [wp] Wikipedia, Skyr (history and Norwegian skjør only)wiki