Flavoured fats & thickeners
Icelandic whey (mysa)
mysa · The pale, slightly tangy liquid by-product drained from skyr curd during traditional Icelandic skyr-making; rich in lactose, milk minerals, and residual whey proteins. Treated as a culinary ingredient — not a waste stream — and the foundation for mysuostur whey cheese, sweet whey soup, and a 1:1 water replacement in Icelandic rye breads.
The formula
~3 L mysa drained per 1 kg skyr curd; for mysuostur reduce 5.75 L whey by ~2/3, add 1/4 cup brown sugar + 2 tbsp butter + 2 tbsp cream
Plate test: a drop sets on a chilled plate when mysuostur is ready.
Identity
- By-product of skyr curdling, traditionally a valued ingredient not waste
- Pale greenish-yellow, mildly tangy, lactose-sweet liquid
- Reduces by ~2/3 to 3/4 to yield a caramel-brown spread (mysuostur)
- Replaces water 1:1 in Icelandic rye sourdough (rúgbrauð)
- Sweet, cinnamon-spiced cornstarch-thickened soup is a traditional use
Ingredients
| Base | fresh skyr whey (mysa) | Use within a few hours of draining; older whey sours and changes color. |
| Sweetener | sugar (brown or white) | Drives lactose caramelization and adds sweetness; 1/4 cup per 5.75 L whey for mysuostur. |
| Seasoning | salt | 1/2 tsp per 5.75 L whey balances the sweetness in mysuostur. |
| Fat | butter | 2 tbsp stirred in at the end of reduction for mysuostur richness. |
| Enrichment | heavy cream | 2 tbsp (or 1–2 cups per gallon in some recipes) stirred in near the end for spreadable texture. |
| Aromatics | cinnamon | Traditional aromatic for sweet whey soup variations. |
| Thickener | potato starch or cornstarch | Slurried in cold whey then stirred into the hot soup to thicken without lumps. |
| Flavor | lemon juice | Used in dessert applications such as skyrfroða where mysuostur is folded into sweetened skyr. |
Method
- 1Drain skyr curd through cheesecloth or a fine strainer and collect the pale greenish-yellow whey that runs off (about 3 L per 1 kg skyr).Capturing the whey fresh preserves its sweetness before stray bacteria sour it further.
- 2Skim any foam or floating curds from the surface; reserve the foam if making mysuostur.The foam carries milk proteins that contribute body and brown color to the finished whey cheese.
- 3Pour the whey into a wide-mouthed heavy pot, add salt, and bring to a boil.A wide, open pot accelerates evaporation so lactose can concentrate and brown.
- 4Boil gently and uncovered, stirring occasionally to prevent sticking, until the whey has reduced by roughly two-thirds (this may take 6–12 hours).Concentration of lactose and milk solids is what produces the characteristic caramel-brown color and sweet flavor.
- 5Stir in the sugar, butter and cream and continue boiling at a full rolling boil, stirring constantly, until a drop sets on a chilled plate.Adding fat at the end prevents scorching and gives the spreadable, fudge-like texture of mysuostur.
- 6(For whey soup) Whisk potato starch or cornstarch into a little cold whey, stir the slurry into the hot reduced whey with sugar and cinnamon, and cook briefly until thickened.A cold slurry keeps starch from lumping; cinnamon complements the caramelized lactose.
- 7Remove from heat and stir gently as the mixture cools; ladle into sterilized jars or bowls and refrigerate.Mysuostur continues to thicken on cooling; gentle stirring prevents sugar crystallization.
Techniques that matter
Open-pot reduction
Uncovered boiling in a wide pot drives off water so lactose can caramelize — the core chemistry of mysuostur.
Skimming the whey foam
Foam is a protein reservoir; reserved and stirred back in for cheese, discarded for clear drinking whey.
Plate test
A drop of reduced whey on a chilled plate reveals whether the cheese will set as it cools.
Variations & derivatives
Mysuostur (soft brown whey cheese)Iceland
Whey reduced by 2/3 then finished with sugar, butter and cream into a spreadable caramel-brown cheese.
MysingurIceland (commercial)
The soft, spreadable supermarket version of mysuostur.
Prim / MyseprimNorway / Scandinavia
Whey cheese cousin made from cheese whey rather than skyr whey.
Whey soup (mysusúpa)Iceland
Sweet, cinnamon-spiced, starch-thickened warm dessert made from reduced whey.
SkyrfroðaIceland
Whipped dessert of grated mysuostur folded into sweetened skyr and cream over plum compote.
Used in these dishes
Substitutions
- skyr whey → cheese whey — Works for mysuostur but flavor skews more savory; sugar compensates.
- brown sugar → white sugar — Produces slightly milder caramelization and lighter color.
- cornstarch → potato starch — Either works for thickening whey soup; potato starch is the traditional Icelandic choice.
- heavy cream → crème fraîche — Similar tang and fat; pour off any liquid that separates.
- butter → omit — Spreads less richly and may scorch more easily.changes result
Troubleshooting
Cheese stays thin and pale
Insufficient reduction — lactose has not yet caramelized. → Continue boiling until volume has dropped by 2/3 to 3/4 and color turns a deep caramel-brown.
Scorched bottom and bitter notes
Stirring too infrequently during the long reduction. → Switch to a heavy-bottomed pot and stir every few minutes; lower the heat as the whey thickens.
Grainy, crystallized cheese
Sugar crystallizing as the cheese cools undisturbed. → Stir gently as it cools, or whisk in a little hot cream to interrupt crystallization.
Sour, off-flavors in the cheese
Whey was left too long before reducing; stray bacteria fermented the lactose. → Use the whey within 24 hours of draining, or boil it briefly to reset before the long reduction.