Reviving old yeast can be a tricky process, as yeast that has gone bad or become inactive is typically beyond repair. However, there are a few steps you can take to try and revive your yeast before giving up and getting a new batch.
1. Check the expiration date: If your yeast is past its expiration date, it's more likely to be inactive. While yeast can sometimes still be viable after the expiration date, it's best to start with fresh yeast if possible.
2. Assess the storage conditions: Yeast is a living organism, and its activity can be affected by how it is stored. If you haven't stored your yeast properly, such as leaving it in a warm or humid environment, it may have become inactive. It's recommended to store yeast in the refrigerator, especially after opening the package.
3. Perform a yeast viability test: To determine if your yeast is still active, you can perform a simple viability test. Dissolve a teaspoon of sugar in a cup of warm water (around 110°F/43°C) and sprinkle your yeast over the surface. Let it sit undisturbed for about 10 minutes. If the yeast starts to foam and bubble, it is likely still alive and can be used. However, if there is no activity, it's a sign that the yeast is no longer viable.
4. Use yeast nutrient: If your yeast seems sluggish but still shows some signs of activity, you can try to revive it by adding yeast nutrient. Yeast nutrient provides essential nutrients that yeast requires for growth and fermentation. Follow the instructions on the yeast nutrient package for the recommended amount to add.
5. Make a yeast starter: If your yeast is showing minimal or no activity, making a yeast starter can help revive it. A yeast starter is essentially a small batch of actively fermenting yeast that can be used to kick-start a larger batch. To make a yeast starter, dissolve a tablespoon of sugar in a cup of warm water, then add your yeast and let it sit for several hours or overnight. If the yeast shows signs of activity and starts to ferment, it can be used to revive larger quantities of yeast.
6. Consider pitching a new batch: If all else fails, it may be best to start fresh with a new batch of yeast. While it can be disappointing to discard a batch of yeast, using old or inactive yeast can result in a failed fermentation or off-flavors in your final product.
Remember, yeast is a living organism, and its viability can be affected by various factors. While it's worth attempting to revive old yeast, it's also important to be prepared with a backup plan in case it doesn't work out.