Homemade Yogurt Culture Ratio Calculator

Making Yogurt at Home

Yogurt is made by fermenting warm milk with live bacterial cultures, primarily Lactobacillus bulgaricus and Streptococcus thermophilus. How much starter goes in and how warm you keep the pot are the two variables that decide everything else.

Starter Culture Ratio

More starter does not make thicker yogurt. It makes faster yogurt, and past a point a grainy one, because the curd sets before the proteins have finished arranging themselves. Too little goes the other way and leaves you with something watery and sour. The range above is narrow for a reason.

Saved starter drifts. Each generation shifts the balance between the two species slightly, and by the sixth or seventh batch the set is usually noticeably weaker. Start fresh when that happens rather than adding more.

Fermentation Temperature

The bacteria have a narrow comfortable band. Outside it they either go dormant or die:

A cooler oven with the light on, or a cooler box with a jar of hot water, holds this range better than most people expect. What kills batches is adding the starter to milk that has not cooled far enough, so use a thermometer for that step even if you eyeball everything else.

The Process

1. Heat the milk to 82°C (180°F). This denatures the whey proteins and is what makes the set firm rather than fragile.
2. Cool to 43°C (109°F). Thermometer, not guesswork.
3. Whisk in the starter.
4. Incubate in the 40 to 43°C band for 4 to 12 hours, depending how tangy you want it.
5. Refrigerate. It thickens again as it chills, so do not judge the set while it is warm.

Thickness Control

Thickness comes from straining and from milk solids, not from extra culture:

• Thicker: strain through cheesecloth. Half an hour firms it up, several hours makes it Greek-style, and a full day makes labneh.
• Even thicker: whisk 2 tbsp of powdered milk per liter into the milk before heating.
• Thinner: lower-fat milk, or pull it out of the incubator earlier.

Fermentation Time Guide

Longer incubation means more tart and more acid, and past about 12 hours it starts weeping whey on its own. Every hour beyond that band costs texture rather than adding flavor.