How to Rehydrate Wine Yeast
This guide explains how to rehydrate wine yeast before adding it to your wine must. We know you’re a true wine making lover who enjoys the process of making, producing, preserving and tasting your homemade wine. That is why today we want to take a closer look at one step that could be confusing for some of you: how to rehydrate your yeast before adding it to your wine must.
TAB Tip: What is “Must”?
“Wine must” is the freshly crushed fruit juice (usually grape juice) that contains the skins, seeds and stems of the fruit. It’s one of the first steps in the wine making process.
Before we begin, bear in mind that you should rehydrate yeast before adding it to the must. Correct rehydration of the yeast can boost the fermentation process and reduce the chance of wine spoilage by bad yeast and bacteria from the grape skins.
It’s also important to remember that yeast is more likely to ferment the wine completely dry, with minimal residual sugar, but only if the yeast is rehydrated properly. With that said, let’s get started on yeast rehydration.
How to rehydrate wine yeast
The first thing you need to do, as we have discussed, is rehydrate the yeast with water before adding it to the must. The second is to measure the temperature of the must beforehand, because, depending on its temperature, there are 2 different methods for hydrating and adding the yeast:
Method A: For red or white must (juice) at 20°C or hotter.
Method B: For colder red must.
Once you have made sure your yeast is properly rehydrated and you have taken the must temperature, you’re good to go!
Method A: must at 20°C or hotter
- Step 1: Select the yeast type required for your homemade wine (aromatic, fast or slow fermenting, etc.) and determine the quantity of yeast required. At The Artisan’s Bottega we recommend 25 grams of yeast per 100 litres of wine. To begin, sterilise a suitable container for the rehydration with boiling water (not with a chemical steriliser). Allow the container to drain and cool, then part-fill a bucket or similar container with water at 38-40°C.
- Step 2: Calculate the weight of yeast required, then add ten times this weight of 38-40°C water to the container you sterilised and place it in the bucket of warm water. Example: 25 grams of yeast requires 250 grams or 250 ml of water.
- Step 3: Weigh the yeast and add it to the sterile bottle. Mix quickly with the water until the yeast is wet. Stop mixing as soon as the yeast is wet, then put the sterile bottle in the bucket for 15 mins without any more mixing. Make sure the temperature is still 38-40°C by topping up the bucket with hot water if necessary.
- Step 4: After 15 minutes, mix the rehydrated yeast briefly and then add it to the must (only if it’s 20°C or hotter). Mix the rehydrated yeast through the must. Remember that if more than 15 minutes elapses (at 38-40°C), the yeast starts to die.
Method B: must colder than 20°C
If your must is colder than 20°C, this is the method you should opt for. Prepare a plastic screw-top bottle of 4 to 20 litres capacity, full of hot water from the tap. Place this bottle in the middle of the crushed grapes. Then follow steps 1-3 above. Right before the end of the 15-minute rehydration period, remove the hot water bottle and check the must’s temperature where the bottle was located (it should be 20-25°C). If it is too hot, mix in a little cool must from the edge. Then pour the rehydrated yeast into this warm area, making sure that you DO NOT mix it, and cover the must.
After several hours, the fermentation process will start, first in the centre of the must, and then it will spread throughout the must in a day or so. Once the skins rise up, plunge the fermentation as normal. 
Rehydrating yeast for white must (juice)
Before we give you this optional tip, it’s important to know that cold-settled white must (juice) needs to warm up to 18-20°C before you add the yeast. Also, bear in mind that the sulphur dioxide in the must can’t exceed 10 ppm free SO2. If you don’t know how to warm up the must, the answer is a microwave oven!
And if by any chance you want to ferment cold, start the ferment at 18-20°C and then wait for the must density to drop by 1-2° Baumé before cooling the must to the desired fermentation temperature.
Congratulations, you’re now a yeast rehydration pro! We know you’re ready to start the wine making process.
Learn the whole wine making process
If you want to learn the whole process of wine making, we have several blog posts, depending on the type of wine you want to produce at home:
And if you follow our tutorials while making your wine, don't forget to tag us on our socials @artisans.bottega and share your pictures! We love checking up on our Artisans Family.
