Commenter pumpkinhead is the second person to doubt my claim that brain weight increases by 9% after death so I thought it would be useful to devote a whole article to this.  The skepticism is understandable since there’s no obvious mechanism by which this should happen.  If I were a theist I might say that when we die we join the spirit world and become omniscient like God and it requires extra brain weight to have all this knowledge.

I first learned about the post-mortem increase by reading J.P. Rushton who cited pg 299 of a 1983 article by Jorgen Voigt  and Henning Pakkenberg  who write:

Appel and Appel [1942a, b] seem to be the first to point out that the brain weight increases post-mortem, mostly during the first 12 h after death, then more slowly,
totalling an average of about 9%. However, experiments with rats [Boyd and Knight,
1963] later showed that the brain weight in these animals does not change very much post-mortem, and the tendency here is to a loss of weight which, in a single experimental group reached a total of 12%. If the results of Appel and Appel [1942a, b] are accepted our brain-weight results should be approximately 9% above the weight in vivo,  as the autopsies are always carried out considerably later than 12 h after death

In the original 1942 article by FW and EM Appel they discuss their equation for predicting brain weight as a function of time since death:

Brain weight (in grams) = 1242.44 + .33 H + 39.72 log H
Here H is the number of hours post mortem.
The curve is certainly suggestive. It suggests that the weight of the brain increases almost continuously after death, at a rate that gradually diminishes. The increase must be limited, but its limit must be beyond the reach of our data. The weight certainly increases for many hours, and possibly it does so for more than 6 days. In the first 12 hours after death the mean weight increases about 47 grams, or nearly 4 percent.
By the end of the second 12-hour period the increase amounts to 63 grams, or more than 5 percent ; by 36 hours it amounts to 74 grams, or nearly 6 percent. If this increase continued for 170 hours after death it would amount to 145 grams, or the amount of the mean loss in weight between ages 25 and 96.
Conjectures as to the implications of this increase are not in order until it has been demonstrated beyond any doubt that the increase is a real phenomenon. Other workers have demonstrated that the weight of the brain varies with the skull dimensions and with the age at death, so there has been no reason to doubt our findings on these points. But no evidence of a post-mortem increase has ever before been presented. It is conceivable that the apparent increase might be due to a chance drift in the age at death, or in the dimensions of the skull, though it is difficult to see why the apparent increase should be essentially continuous and at a gradually diminishing rate if any accident of sampling or distribution is responsible for it. Still, the possibility needs to be investigated


Here’s their data for the brain weight increase, so judge for yourselves how convincing it is.