Comparison – ‘top’ and ‘bottom’ fermenting yeast
Thought I’d throw up a quick pic for anyone who’s interested in seeing ‘top’ and ‘bottom’ fermenting yeast at work.
Although the yeast in each FV is distributed throughout the wort, the ale yeast on the left (Safale US-05) has created a thick foamy head on top. The lager yeast (WLP810 San Francisco Lager) on the right has a clean white head on top with no foam layer.
Both yeast types were pitched at the same temp (16 deg C), into the same batch of wort (for a Californian Common), and have been fermenting side by side for 36 hours at 15 – 16 deg C. The only variable that’s different here (within reason) is the yeast type, as I wanted to see how they compared (based on this article here ). It will certainly be interesting to see how this one turns out.
Normally ale and lager yeasts ferment at different ends of the temperature scale and never the twain shall meet. The WLP810 is different in this regard, as it’s a lager yeast that ferments at temperatures usually only suited to ale yeasts.
The ideal temp ranges for both are as follows – WLP810 (14 – 18 deg C) and S-05 (15 – 22 deg C). So for these two yeasts there’s a cross over point where they’ll both do well, and I chose 16 deg C as being that happy place for each.
The WLP810 can be used in other styles, but is particularly associated with the Californian Common. The US-05 seems to fit the requirements of this style well as it makes for a good clean ferment with low diacatyl at the lower end of it’s ideal temp, so I would expect a similar profile in the finished beer – although who knows what will happen in practice, that’s half the fun of brewing .
The real question I guess I’m trying to answer here is whether the beer made using US-05 will give that same clean lager taste as the WLP810. (S-05 is less expensive, and as it’s a dried yeast is a little less fuss).
[UPDATE – from 22/11/2014]
It’s been a busy month, so slight delay in getting these pics up. Both beers are currently conditioning in bottles, and I’ll be posting tasting notes for each in a week or two, for anyone who’s interested.
All photos below were taken on 22 November (6 days after pitching). The primary phase of fermentation had completed in both FVs by that stage, and the krausen had fallen back into the wort.
Figure 1: Top of demijohns – After Day 4 the heavy foam on top of the wort with US-05 began to break up and sink to the bottom in clumps. The yeast in the WLP810 demijohn began flocculating also, but in a less spectacular fashion. Although not entirely clear from the photo above, the wort in the US-05 demijohn was relatively clear on Day 6, whereas the WLP810 wort was still quite cloudy.
Figure 2: Side by side comparison – The clarity of the US-05 wort is more apparent in the pic above, although the biggest difference to be noted is the level of wort in both FVs and the amount of yeast in the WLP810 blow-off container. There was equally vigorous fermentation in both FVs, but the lighter foam in the WLP810 demijohn seemed to travel through the blow-off tube more readily, resulting in a loss of wort and quite a bit of yeast.
In this trial there’s no way of knowing if the loss of yeast affected the fermentation negatively, but if I was fermenting with this setup again I would use a sealed and sanitised blow-off container (with airlock), and collect the yeast beneath pre-boiled water. It seemed like a shame to waste all that good yeast.
The thick foam layer on top of the US-05 FV appeared to prevent the same losses of wort and krausen, although when the foam fell to the bottom it did create a thicker layer of crud than in the WLP810 FV. In real terms this meant that, despite losing some wort to blow-off in the WLP810 FV, I actually got about the same volume of beer at bottling time from both FVs.
Figure 3: Bottom of demijohns – The amount of yeast lost through the blow-off tube of the WLP810 San Francisco Lager FV is really clear in the photo above, with just a slight coating of yeast in the bottom of the Safale US-05 blow-off container. The colour of the water in the WLP810 container also tells a story about how much wort was lost through the blow-off tube.
Another interesting observation is the very clear white layer in the trub at the bottom of the WLP810 FV. The same thin layer can even be seen in the trub at the bottom of the WLP810 blow-off container. No such layer was seen in the US-05 FV.
(Updates to follow)
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