The same is not true in homebrewing. Yeast costs are much smaller for homebrewers, so there is less incentive to try to save money by reusing yeast (if you are making your own beer solely to save money, you may be in the wrong hobby). Homebrewers also do not have much experience with saving yeast and performing proper procedures to limit bacterial load and optimize yeast health. But, the largest reason for not reusing yeast, in my opinion, is scheduling. Liquid yeast does not have a long storage life, even in optimal conditions. If a homebrewer saves a batch of yeast and does not use it within two weeks, the yeast may need a starter to revitalize it before repitching. Most homebrewers I know do not brew more than once or twice a month, so storage becomes a problem. Combine this with the fact that we rarely brew the same beer style back-to-back, often using different yeasts, so scheduling becomes quite an issue.
All that being said, I have intended to reuse a batch of yeast for more than one beer for quite some time. The easiest way to do this is to ferment a batch of beer, siphon the new beer off the cake, and have fresh wort ready to go on the yeast immediately afterwards. This method does not require rinsing the yeast; nor does it require lengthy yeast storage. It is a simple process, but requires planning to time the two batches properly and ensure they can use the same yeast (I did an Irish Red and an Oatmeal Stout with White Lab's Irish Ale Yeast).
If you consider reusing a yeast cake, keep the following in mind:
- Do not use the same cake more than two or three times. Because you are not rinsing the yeast, each batch leaves trub, hop matter, and dead yeast behind. This can slowly degrade and produce off-flavors in your beer.
- Do not use a high-gravity wort or very hoppy wort until the terminal batch of beer. High-gravity wort stresses the yeast and may make it less likely to fully ferment the following beer. Highly-hopped worts leave bittering compounds in the yeast cake that can over-bitter the subsequent beer.
- Target a yeast that settles out well, so that it is easy to rack off the yeast cake and not have it be overly disturbed before receiving the new wort
- Avoid using fining agents, like gelatin, that will be left in the yeast cake and can inhibit the subsequent fermentation.
- Be prepared for VERY quick yeast activity and use a blow-off tube because of the violence of subsequent fermentations (see the picture for what my Oatmeal Stout left in the fermentation chamber)